Multi-viscosity motor oils are not exactly what some people think
01-07-2016, 02:48 PM
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Multi-viscosity motor oils are not exactly what some people think
Multi-viscosity motor oils are in “one way” what most people think they are. And that is, rated as a thinner viscosity when cold, than when they are hot. But, that’s where it ends for many people, because the details are NOT as simple as they might seem. So, many people get confused and misunderstand what all this means.
When cautioned about running a stone-cold engine too hard, some will say they don’t have to worry about that because they are running a multi-viscosity oil. And that is not coming from kids in High School Auto Shop Class who are just starting out. That has come from old timers who have been car guys for decades, and they still do not understand how multi-viscosity motor oil works. So, here is some basic motor oil tech information to clear things up.
• A multi-viscosity motor oil is identified by its viscosity rating at two temperatures. It is rated at the cold temperature of 0*F, which is represented by the first number, the one in front of the “W”. It is also rated at the hot temperature of 212*F, which is represented by the second number, the one after the “W”. For example, 5W30 is rated as a 5wt when cold and rated as a 30wt when hot. These are the type of numbers everyone is most familiar with.
But, that DOES NOT mean that 5W30 is thinner when it is cold. And that is where people get confused and misunderstand what is really going on. The confusion comes in because of the temperatures at which the oil was rated. 0*F and 212*F are apples and oranges, or two completely different scales.
• EVERY motor oil thins out as it heats up and thickens as it cools down, no matter if it is a straight weight or a multi-viscosity. You can get a feel for this by checking the oil on your dipstick when it is cold, thick, and drips slowly. Then check it again when it is hot, thin, and drips almost like water. And keep in mind that thinner oil flows more freely through all the restrictions inside an engine, compared to thicker oil that flows more slowly through those restrictions.
Mechanical Engineers design engines with certain clearances, to be used with a certain motor oil viscosity, in order to provide the proper oil flow rate/lubrication/cooling needed for a long and trouble free life. Of course the engine has to start-up and run when cold, but it will spend 99% of its operational life at normal operating temperatures. So, if an engine was designed to use 5W30, that means it was intended to be properly lubricated 99% of the time, by a motor oil rated as a 30wt when hot.
But, also keep in mind that oil pressure, in and of itself, is NOT what we are after. Oil pressure is only a measurement of resistance to flow. And oil pressure is NOT lubrication. You can have lots of oil pressure, such as at cold start-up, while at the same time having very little oil flow, such as with heavy viscosity oil, which is NOT a good thing. We need oil pressure only to generate the oil flow we need. Oil FLOW is lubrication, so that is what we are after.
And any reduction in the intended oil flow rate/lubrication, would compromise the wear protection an engine was designed to have. Of course oil flow rate/lubrication is important throughout an engine, but it is extremely important to have sufficient oil flow to maintain the incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings. And any oil thicker than a hot 30wt for the engine example above, would reduce that intended oil flow rate/lubrication. If the flow rate/lubrication is reduced enough, unnecessary wear can occur. And if flow rate/lubrication is reduced even more, actual engine damage can result (more on that below).
So, let’s take a look at what is specifically going on with motor oil at cold start-up vs what is going on with it at hot operating temperature. For this comparison purpose, multi-grade motor oil viscosity properties are typically given at 40*C (104*F) and at 100*C (212*F). And its thickness is given in an accurate measurement called centistokes (cSt).
The cold 40*C (104*F which is only slightly above normal temperature for humans) temperature shown below will be used to represent cold start-up conditions, though at more common colder temperatures, the oil will be even thicker yet. And the hot 100*C (212*F) temperature shown below will be used to represent hot operating conditions, though at more common higher temperatures, the oil will be thinner yet. Keep in mind, as mentioned above, EVERY motor oil thins out as it heats up and thickens as it cools down, no matter what its identifying viscosity rating is.
Actual Motor Oil thickness
cSt @ cold 40*C (104*F) / cSt @ hot 100*C (212*F)
0W40 = 79.9 / 14.3, or 5.6 times thicker when cold
5W20 = 51.6 / 9.0, or 5.7 times thicker when cold
5W30 = 64.8 / 10.7, or 6.1 times thicker when cold
5W40 = 93.7 / 15.7, or 6.0 times thicker when cold
10W30 = 71.8 / 11.5, or 6.2 times thicker when cold
10W40 = 89.9 / 13.8, or 6.5 times thicker when cold
15W40 = 105.0 / 14.8, or 7.1 times thicker when cold
20W50 = 170.0 / 20.2, or 8.4 times thicker when cold
As you can see above, even at these modest cold and hot temperatures that motor oil thickness values are typically available for, the oil is WAY, WAY THICKER when cold, than it is when hot. And the difference is even GREATER at more normal colder start-up and hotter operational temperatures. So, that means that at cold start-up, oil flow rate/lubrication will be GREATLY REDUCED, even if you are using the recommended multi-viscosity motor oil. But even so, multi-viscosity oils are still a good thing, because they would be even thicker yet when cold, if they were straight wt oils.
NOTE: This will likely surprise a lot of people. Notice that cold 5W20 at 51.6 cSt, is 2.6 times THICKER, than hot 20W50 at 20.2 cSt. Now you know that a low viscosity cold rating does NOT mean the oil is thin when it’s cold.
CONCLUSION:
The best way to protect your engine, when dealing with thick, poor flowing, cold oil, is simple. If you run an engine too hard when it’s stone-cold, you can cause unnecessary wear or even damage, due to the reduced oil flow rate/lubrication. But, all you have to do to avoid that problem, and to protect your engine, is to run it easy (small throttle openings and low rpm) for the 10 or 15 minutes it takes for it to reach normal operating temperature. All you need is a little patience, and then you can run it hard without any concern about lubrication.
NOTE: You DO NOT need to start-up your engine, then let it sit and idle to warm-up. That is a complete waste of fuel, and makes useless exhaust pollution for absolutely no good reason. Just start it up, put it in gear, and drive it easy, as discussed just above, until it is fully warmed up.
But, if you don’t have the patience to wait for an engine to reach normal operating temperature before hammering it, then here is an example of what can happen to it. I have a next door neighbor lady who used to drive a Chevy Tahoe SUV. And when I happened so see her leave in the morning, I noticed that she would back out of her driveway, put it in Drive, and floor it………on a stone-cold engine. I thought, if she keeps that up, she’s going to ruin her engine. And every time I saw her leave, that was her normal routine. Of course she is just a normal lady who is not the least bit technical, so she had no idea she was doing anything wrong. To her, flooring her Tahoe with a stone-cold engine, was no different than switching her blender on to “high”.
She kept up that routine for maybe a year or more. Then when I would happen to see her leave, I started hearing a rod knock as she took off, which didn’t surprise me at all. And she continued to drive it like that for maybe another year. But, the knock continued to get worse over time, which is a perfect example of the engine not having sufficient oil flow to fully maintain the extremely important incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings.
The rod knock finally got so bad, that she traded the Tahoe off for another vehicle. Funny thing, someone must have clued her in, because she has never once driven the new vehicle like that. And it has been fine now for two or three years. I guess she learned her lesson……..the hard way. So, it would be wise to learn from her mistake and avoid doing the same thing to your own engine.
For more info about motor oil wear protection, that is not just opinion or theory, see my "TECH FACTS, NOT MYTHS" Blog, which now has over 145,000 views worldwide. You can see the Blog and my entire 170+ motor oil “Wear Protection Ranking List”, which is "proven" by the Physics and Chemistry involved, and EXACTLY matches real world severe over-heating experience, real world Track experience, real world flat tappet break-in experience, and real world High Performance Street experience (test data validation doesn’t get any better than this), along with additional motor oil tech FACTS, by going to the Blog link below. Credentials, methodology, proof, facts, data, Industry endorsements, real world validation, etc, are all included in the Blog. See for yourself, the engine you save may be your own.
http://540ratblog.wordpress.com/
540 RAT
When cautioned about running a stone-cold engine too hard, some will say they don’t have to worry about that because they are running a multi-viscosity oil. And that is not coming from kids in High School Auto Shop Class who are just starting out. That has come from old timers who have been car guys for decades, and they still do not understand how multi-viscosity motor oil works. So, here is some basic motor oil tech information to clear things up.
• A multi-viscosity motor oil is identified by its viscosity rating at two temperatures. It is rated at the cold temperature of 0*F, which is represented by the first number, the one in front of the “W”. It is also rated at the hot temperature of 212*F, which is represented by the second number, the one after the “W”. For example, 5W30 is rated as a 5wt when cold and rated as a 30wt when hot. These are the type of numbers everyone is most familiar with.
But, that DOES NOT mean that 5W30 is thinner when it is cold. And that is where people get confused and misunderstand what is really going on. The confusion comes in because of the temperatures at which the oil was rated. 0*F and 212*F are apples and oranges, or two completely different scales.
• EVERY motor oil thins out as it heats up and thickens as it cools down, no matter if it is a straight weight or a multi-viscosity. You can get a feel for this by checking the oil on your dipstick when it is cold, thick, and drips slowly. Then check it again when it is hot, thin, and drips almost like water. And keep in mind that thinner oil flows more freely through all the restrictions inside an engine, compared to thicker oil that flows more slowly through those restrictions.
Mechanical Engineers design engines with certain clearances, to be used with a certain motor oil viscosity, in order to provide the proper oil flow rate/lubrication/cooling needed for a long and trouble free life. Of course the engine has to start-up and run when cold, but it will spend 99% of its operational life at normal operating temperatures. So, if an engine was designed to use 5W30, that means it was intended to be properly lubricated 99% of the time, by a motor oil rated as a 30wt when hot.
But, also keep in mind that oil pressure, in and of itself, is NOT what we are after. Oil pressure is only a measurement of resistance to flow. And oil pressure is NOT lubrication. You can have lots of oil pressure, such as at cold start-up, while at the same time having very little oil flow, such as with heavy viscosity oil, which is NOT a good thing. We need oil pressure only to generate the oil flow we need. Oil FLOW is lubrication, so that is what we are after.
And any reduction in the intended oil flow rate/lubrication, would compromise the wear protection an engine was designed to have. Of course oil flow rate/lubrication is important throughout an engine, but it is extremely important to have sufficient oil flow to maintain the incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings. And any oil thicker than a hot 30wt for the engine example above, would reduce that intended oil flow rate/lubrication. If the flow rate/lubrication is reduced enough, unnecessary wear can occur. And if flow rate/lubrication is reduced even more, actual engine damage can result (more on that below).
So, let’s take a look at what is specifically going on with motor oil at cold start-up vs what is going on with it at hot operating temperature. For this comparison purpose, multi-grade motor oil viscosity properties are typically given at 40*C (104*F) and at 100*C (212*F). And its thickness is given in an accurate measurement called centistokes (cSt).
The cold 40*C (104*F which is only slightly above normal temperature for humans) temperature shown below will be used to represent cold start-up conditions, though at more common colder temperatures, the oil will be even thicker yet. And the hot 100*C (212*F) temperature shown below will be used to represent hot operating conditions, though at more common higher temperatures, the oil will be thinner yet. Keep in mind, as mentioned above, EVERY motor oil thins out as it heats up and thickens as it cools down, no matter what its identifying viscosity rating is.
Actual Motor Oil thickness
cSt @ cold 40*C (104*F) / cSt @ hot 100*C (212*F)
0W40 = 79.9 / 14.3, or 5.6 times thicker when cold
5W20 = 51.6 / 9.0, or 5.7 times thicker when cold
5W30 = 64.8 / 10.7, or 6.1 times thicker when cold
5W40 = 93.7 / 15.7, or 6.0 times thicker when cold
10W30 = 71.8 / 11.5, or 6.2 times thicker when cold
10W40 = 89.9 / 13.8, or 6.5 times thicker when cold
15W40 = 105.0 / 14.8, or 7.1 times thicker when cold
20W50 = 170.0 / 20.2, or 8.4 times thicker when cold
As you can see above, even at these modest cold and hot temperatures that motor oil thickness values are typically available for, the oil is WAY, WAY THICKER when cold, than it is when hot. And the difference is even GREATER at more normal colder start-up and hotter operational temperatures. So, that means that at cold start-up, oil flow rate/lubrication will be GREATLY REDUCED, even if you are using the recommended multi-viscosity motor oil. But even so, multi-viscosity oils are still a good thing, because they would be even thicker yet when cold, if they were straight wt oils.
NOTE: This will likely surprise a lot of people. Notice that cold 5W20 at 51.6 cSt, is 2.6 times THICKER, than hot 20W50 at 20.2 cSt. Now you know that a low viscosity cold rating does NOT mean the oil is thin when it’s cold.
CONCLUSION:
The best way to protect your engine, when dealing with thick, poor flowing, cold oil, is simple. If you run an engine too hard when it’s stone-cold, you can cause unnecessary wear or even damage, due to the reduced oil flow rate/lubrication. But, all you have to do to avoid that problem, and to protect your engine, is to run it easy (small throttle openings and low rpm) for the 10 or 15 minutes it takes for it to reach normal operating temperature. All you need is a little patience, and then you can run it hard without any concern about lubrication.
NOTE: You DO NOT need to start-up your engine, then let it sit and idle to warm-up. That is a complete waste of fuel, and makes useless exhaust pollution for absolutely no good reason. Just start it up, put it in gear, and drive it easy, as discussed just above, until it is fully warmed up.
But, if you don’t have the patience to wait for an engine to reach normal operating temperature before hammering it, then here is an example of what can happen to it. I have a next door neighbor lady who used to drive a Chevy Tahoe SUV. And when I happened so see her leave in the morning, I noticed that she would back out of her driveway, put it in Drive, and floor it………on a stone-cold engine. I thought, if she keeps that up, she’s going to ruin her engine. And every time I saw her leave, that was her normal routine. Of course she is just a normal lady who is not the least bit technical, so she had no idea she was doing anything wrong. To her, flooring her Tahoe with a stone-cold engine, was no different than switching her blender on to “high”.
She kept up that routine for maybe a year or more. Then when I would happen to see her leave, I started hearing a rod knock as she took off, which didn’t surprise me at all. And she continued to drive it like that for maybe another year. But, the knock continued to get worse over time, which is a perfect example of the engine not having sufficient oil flow to fully maintain the extremely important incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings.
The rod knock finally got so bad, that she traded the Tahoe off for another vehicle. Funny thing, someone must have clued her in, because she has never once driven the new vehicle like that. And it has been fine now for two or three years. I guess she learned her lesson……..the hard way. So, it would be wise to learn from her mistake and avoid doing the same thing to your own engine.
For more info about motor oil wear protection, that is not just opinion or theory, see my "TECH FACTS, NOT MYTHS" Blog, which now has over 145,000 views worldwide. You can see the Blog and my entire 170+ motor oil “Wear Protection Ranking List”, which is "proven" by the Physics and Chemistry involved, and EXACTLY matches real world severe over-heating experience, real world Track experience, real world flat tappet break-in experience, and real world High Performance Street experience (test data validation doesn’t get any better than this), along with additional motor oil tech FACTS, by going to the Blog link below. Credentials, methodology, proof, facts, data, Industry endorsements, real world validation, etc, are all included in the Blog. See for yourself, the engine you save may be your own.
http://540ratblog.wordpress.com/
540 RAT
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Tropicana (01-09-2016)
01-07-2016, 04:01 PM
#2
Burning Brakes
Great write up! Personally, I kind of have 'OCD' when it comes to oil changes & engine warm up process stuff. Great to re-read what I'm already a firm advocate of. Multi-viscosity motor oils are in “one way” what most people think they are. And that is, rated as a thinner viscosity when cold, than when they are hot. But, that’s where it ends for many people, because the details are NOT as simple as they might seem. So, many people get confused and misunderstand what all this means.
When cautioned about running a stone-cold engine too hard, some will say they don’t have to worry about that because they are running a multi-viscosity oil. And that is not coming from kids in High School Auto Shop Class who are just starting out. That has come from old timers who have been car guys for decades, and they still do not understand how multi-viscosity motor oil works. So, here is some basic motor oil tech information to clear things up.
• A multi-viscosity motor oil is identified by its viscosity rating at two temperatures. It is rated at the cold temperature of 0*F, which is represented by the first number, the one in front of the “W”. It is also rated at the hot temperature of 212*F, which is represented by the second number, the one after the “W”. For example, 5W30 is rated as a 5wt when cold and rated as a 30wt when hot. These are the type of numbers everyone is most familiar with.
But, that DOES NOT mean that 5W30 is thinner when it is cold. And that is where people get confused and misunderstand what is really going on. The confusion comes in because of the temperatures at which the oil was rated. 0*F and 212*F are apples and oranges, or two completely different scales.
• EVERY motor oil thins out as it heats up and thickens as it cools down, no matter if it is a straight weight or a multi-viscosity. You can get a feel for this by checking the oil on your dipstick when it is cold, thick, and drips slowly. Then check it again when it is hot, thin, and drips almost like water. And keep in mind that thinner oil flows more freely through all the restrictions inside an engine, compared to thicker oil that flows more slowly through those restrictions.
Mechanical Engineers design engines with certain clearances, to be used with a certain motor oil viscosity, in order to provide the proper oil flow rate/lubrication/cooling needed for a long and trouble free life. Of course the engine has to start-up and run when cold, but it will spend 99% of its operational life at normal operating temperatures. So, if an engine was designed to use 5W30, that means it was intended to be properly lubricated 99% of the time, by a motor oil rated as a 30wt when hot.
But, also keep in mind that oil pressure, in and of itself, is NOT what we are after. Oil pressure is only a measurement of resistance to flow. And oil pressure is NOT lubrication. You can have lots of oil pressure, such as at cold start-up, while at the same time having very little oil flow, such as with heavy viscosity oil, which is NOT a good thing. We need oil pressure only to generate the oil flow we need. Oil FLOW is lubrication, so that is what we are after.
And any reduction in the intended oil flow rate/lubrication, would compromise the wear protection an engine was designed to have. Of course oil flow rate/lubrication is important throughout an engine, but it is extremely important to have sufficient oil flow to maintain the incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings. And any oil thicker than a hot 30wt for the engine example above, would reduce that intended oil flow rate/lubrication. If the flow rate/lubrication is reduced enough, unnecessary wear can occur. And if flow rate/lubrication is reduced even more, actual engine damage can result (more on that below).
So, let’s take a look at what is specifically going on with motor oil at cold start-up vs what is going on with it at hot operating temperature. For this comparison purpose, multi-grade motor oil viscosity properties are typically given at 40*C (104*F) and at 100*C (212*F). And its thickness is given in an accurate measurement called centistokes (cSt).
The cold 40*C (104*F which is only slightly above normal temperature for humans) temperature shown below will be used to represent cold start-up conditions, though at more common colder temperatures, the oil will be even thicker yet. And the hot 100*C (212*F) temperature shown below will be used to represent hot operating conditions, though at more common higher temperatures, the oil will be thinner yet. Keep in mind, as mentioned above, EVERY motor oil thins out as it heats up and thickens as it cools down, no matter what its identifying viscosity rating is.
Actual Motor Oil thickness
cSt @ cold 40*C (104*F) / cSt @ hot 100*C (212*F)
0W40 = 79.9 / 14.3, or 5.6 times thicker when cold
5W20 = 51.6 / 9.0, or 5.7 times thicker when cold
5W30 = 64.8 / 10.7, or 6.1 times thicker when cold
5W40 = 93.7 / 15.7, or 6.0 times thicker when cold
10W30 = 71.8 / 11.5, or 6.2 times thicker when cold
10W40 = 89.9 / 13.8, or 6.5 times thicker when cold
15W40 = 105.0 / 14.8, or 7.1 times thicker when cold
20W50 = 170.0 / 20.2, or 8.4 times thicker when cold
As you can see above, even at these modest cold and hot temperatures that motor oil thickness values are typically available for, the oil is WAY, WAY THICKER when cold, than it is when hot. And the difference is even GREATER at more normal colder start-up and hotter operational temperatures. So, that means that at cold start-up, oil flow rate/lubrication will be GREATLY REDUCED, even if you are using the recommended multi-viscosity motor oil. But even so, multi-viscosity oils are still a good thing, because they would be even thicker yet when cold, if they were straight wt oils.
NOTE: This will likely surprise a lot of people. Notice that cold 5W20 at 51.6 cSt, is 2.6 times THICKER, than hot 20W50 at 20.2 cSt. Now you know that a low viscosity cold rating does NOT mean the oil is thin when it’s cold.
CONCLUSION:
The best way to protect your engine, when dealing with thick, poor flowing, cold oil, is simple. If you run an engine too hard when it’s stone-cold, you can cause unnecessary wear or even damage, due to the reduced oil flow rate/lubrication. But, all you have to do to avoid that problem, and to protect your engine, is to run it easy (small throttle openings and low rpm) for the 10 or 15 minutes it takes for it to reach normal operating temperature. All you need is a little patience, and then you can run it hard without any concern about lubrication.
NOTE: You DO NOT need to start-up your engine, then let it sit and idle to warm-up. That is a complete waste of fuel, and makes useless exhaust pollution for absolutely no good reason. Just start it up, put it in gear, and drive it easy, as discussed just above, until it is fully warmed up.
But, if you don’t have the patience to wait for an engine to reach normal operating temperature before hammering it, then here is an example of what can happen to it. I have a next door neighbor lady who used to drive a Chevy Tahoe SUV. And when I happened so see her leave in the morning, I noticed that she would back out of her driveway, put it in Drive, and floor it………on a stone-cold engine. I thought, if she keeps that up, she’s going to ruin her engine. And every time I saw her leave, that was her normal routine. Of course she is just a normal lady who is not the least bit technical, so she had no idea she was doing anything wrong. To her, flooring her Tahoe with a stone-cold engine, was no different than switching her blender on to “high”.
She kept up that routine for maybe a year or more. Then when I would happen to see her leave, I started hearing a rod knock as she took off, which didn’t surprise me at all. And she continued to drive it like that for maybe another year. But, the knock continued to get worse over time, which is a perfect example of the engine not having sufficient oil flow to fully maintain the extremely important incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings.
The rod knock finally got so bad, that she traded the Tahoe off for another vehicle. Funny thing, someone must have clued her in, because she has never once driven the new vehicle like that. And it has been fine now for two or three years. I guess she learned her lesson……..the hard way. So, it would be wise to learn from her mistake and avoid doing the same thing to your own engine.
For more info about motor oil wear protection, that is not just opinion or theory, see my "TECH FACTS, NOT MYTHS" Blog, which now has over 145,000 views worldwide. You can see the Blog and my entire 170+ motor oil “Wear Protection Ranking List”, which is "proven" by the Physics and Chemistry involved, and EXACTLY matches real world severe over-heating experience, real world Track experience, real world flat tappet break-in experience, and real world High Performance Street experience (test data validation doesn’t get any better than this), along with additional motor oil tech FACTS, by going to the Blog link below. Credentials, methodology, proof, facts, data, Industry endorsements, real world validation, etc, are all included in the Blog. See for yourself, the engine you save may be your own.
http://540ratblog.wordpress.com/
540 RAT
When cautioned about running a stone-cold engine too hard, some will say they don’t have to worry about that because they are running a multi-viscosity oil. And that is not coming from kids in High School Auto Shop Class who are just starting out. That has come from old timers who have been car guys for decades, and they still do not understand how multi-viscosity motor oil works. So, here is some basic motor oil tech information to clear things up.
• A multi-viscosity motor oil is identified by its viscosity rating at two temperatures. It is rated at the cold temperature of 0*F, which is represented by the first number, the one in front of the “W”. It is also rated at the hot temperature of 212*F, which is represented by the second number, the one after the “W”. For example, 5W30 is rated as a 5wt when cold and rated as a 30wt when hot. These are the type of numbers everyone is most familiar with.
But, that DOES NOT mean that 5W30 is thinner when it is cold. And that is where people get confused and misunderstand what is really going on. The confusion comes in because of the temperatures at which the oil was rated. 0*F and 212*F are apples and oranges, or two completely different scales.
• EVERY motor oil thins out as it heats up and thickens as it cools down, no matter if it is a straight weight or a multi-viscosity. You can get a feel for this by checking the oil on your dipstick when it is cold, thick, and drips slowly. Then check it again when it is hot, thin, and drips almost like water. And keep in mind that thinner oil flows more freely through all the restrictions inside an engine, compared to thicker oil that flows more slowly through those restrictions.
Mechanical Engineers design engines with certain clearances, to be used with a certain motor oil viscosity, in order to provide the proper oil flow rate/lubrication/cooling needed for a long and trouble free life. Of course the engine has to start-up and run when cold, but it will spend 99% of its operational life at normal operating temperatures. So, if an engine was designed to use 5W30, that means it was intended to be properly lubricated 99% of the time, by a motor oil rated as a 30wt when hot.
But, also keep in mind that oil pressure, in and of itself, is NOT what we are after. Oil pressure is only a measurement of resistance to flow. And oil pressure is NOT lubrication. You can have lots of oil pressure, such as at cold start-up, while at the same time having very little oil flow, such as with heavy viscosity oil, which is NOT a good thing. We need oil pressure only to generate the oil flow we need. Oil FLOW is lubrication, so that is what we are after.
And any reduction in the intended oil flow rate/lubrication, would compromise the wear protection an engine was designed to have. Of course oil flow rate/lubrication is important throughout an engine, but it is extremely important to have sufficient oil flow to maintain the incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings. And any oil thicker than a hot 30wt for the engine example above, would reduce that intended oil flow rate/lubrication. If the flow rate/lubrication is reduced enough, unnecessary wear can occur. And if flow rate/lubrication is reduced even more, actual engine damage can result (more on that below).
So, let’s take a look at what is specifically going on with motor oil at cold start-up vs what is going on with it at hot operating temperature. For this comparison purpose, multi-grade motor oil viscosity properties are typically given at 40*C (104*F) and at 100*C (212*F). And its thickness is given in an accurate measurement called centistokes (cSt).
The cold 40*C (104*F which is only slightly above normal temperature for humans) temperature shown below will be used to represent cold start-up conditions, though at more common colder temperatures, the oil will be even thicker yet. And the hot 100*C (212*F) temperature shown below will be used to represent hot operating conditions, though at more common higher temperatures, the oil will be thinner yet. Keep in mind, as mentioned above, EVERY motor oil thins out as it heats up and thickens as it cools down, no matter what its identifying viscosity rating is.
Actual Motor Oil thickness
cSt @ cold 40*C (104*F) / cSt @ hot 100*C (212*F)
0W40 = 79.9 / 14.3, or 5.6 times thicker when cold
5W20 = 51.6 / 9.0, or 5.7 times thicker when cold
5W30 = 64.8 / 10.7, or 6.1 times thicker when cold
5W40 = 93.7 / 15.7, or 6.0 times thicker when cold
10W30 = 71.8 / 11.5, or 6.2 times thicker when cold
10W40 = 89.9 / 13.8, or 6.5 times thicker when cold
15W40 = 105.0 / 14.8, or 7.1 times thicker when cold
20W50 = 170.0 / 20.2, or 8.4 times thicker when cold
As you can see above, even at these modest cold and hot temperatures that motor oil thickness values are typically available for, the oil is WAY, WAY THICKER when cold, than it is when hot. And the difference is even GREATER at more normal colder start-up and hotter operational temperatures. So, that means that at cold start-up, oil flow rate/lubrication will be GREATLY REDUCED, even if you are using the recommended multi-viscosity motor oil. But even so, multi-viscosity oils are still a good thing, because they would be even thicker yet when cold, if they were straight wt oils.
NOTE: This will likely surprise a lot of people. Notice that cold 5W20 at 51.6 cSt, is 2.6 times THICKER, than hot 20W50 at 20.2 cSt. Now you know that a low viscosity cold rating does NOT mean the oil is thin when it’s cold.
CONCLUSION:
The best way to protect your engine, when dealing with thick, poor flowing, cold oil, is simple. If you run an engine too hard when it’s stone-cold, you can cause unnecessary wear or even damage, due to the reduced oil flow rate/lubrication. But, all you have to do to avoid that problem, and to protect your engine, is to run it easy (small throttle openings and low rpm) for the 10 or 15 minutes it takes for it to reach normal operating temperature. All you need is a little patience, and then you can run it hard without any concern about lubrication.
NOTE: You DO NOT need to start-up your engine, then let it sit and idle to warm-up. That is a complete waste of fuel, and makes useless exhaust pollution for absolutely no good reason. Just start it up, put it in gear, and drive it easy, as discussed just above, until it is fully warmed up.
But, if you don’t have the patience to wait for an engine to reach normal operating temperature before hammering it, then here is an example of what can happen to it. I have a next door neighbor lady who used to drive a Chevy Tahoe SUV. And when I happened so see her leave in the morning, I noticed that she would back out of her driveway, put it in Drive, and floor it………on a stone-cold engine. I thought, if she keeps that up, she’s going to ruin her engine. And every time I saw her leave, that was her normal routine. Of course she is just a normal lady who is not the least bit technical, so she had no idea she was doing anything wrong. To her, flooring her Tahoe with a stone-cold engine, was no different than switching her blender on to “high”.
She kept up that routine for maybe a year or more. Then when I would happen to see her leave, I started hearing a rod knock as she took off, which didn’t surprise me at all. And she continued to drive it like that for maybe another year. But, the knock continued to get worse over time, which is a perfect example of the engine not having sufficient oil flow to fully maintain the extremely important incompressible hydrodynamic liquid oil wedge that is formed between the crankshaft journals and the rod and main bearings.
The rod knock finally got so bad, that she traded the Tahoe off for another vehicle. Funny thing, someone must have clued her in, because she has never once driven the new vehicle like that. And it has been fine now for two or three years. I guess she learned her lesson……..the hard way. So, it would be wise to learn from her mistake and avoid doing the same thing to your own engine.
For more info about motor oil wear protection, that is not just opinion or theory, see my "TECH FACTS, NOT MYTHS" Blog, which now has over 145,000 views worldwide. You can see the Blog and my entire 170+ motor oil “Wear Protection Ranking List”, which is "proven" by the Physics and Chemistry involved, and EXACTLY matches real world severe over-heating experience, real world Track experience, real world flat tappet break-in experience, and real world High Performance Street experience (test data validation doesn’t get any better than this), along with additional motor oil tech FACTS, by going to the Blog link below. Credentials, methodology, proof, facts, data, Industry endorsements, real world validation, etc, are all included in the Blog. See for yourself, the engine you save may be your own.
http://540ratblog.wordpress.com/
540 RAT
01-07-2016, 04:18 PM
#3
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Location: Raleigh, NC
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St. Jude Donor '15
So, what oil should I use? 
01-07-2016, 09:04 PM
#4
Burning Brakes
01-07-2016, 09:08 PM
#5
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Location: Raleigh, NC
Posts: 16,664
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St. Jude Donor '15
lol, I've been using Mobil 1 Euro 0w40. Seems to be pretty decent stuff for something you can still buy at Walmart
Cool site though by the way...
Cool site though by the way...
01-08-2016, 10:49 AM
#8
Burning Brakes
This is just my thought on the matter...I've heard that most engine wear in a cold/hot cycle of an engine will happen when you first start it up. So as the engine is getting up to operating temperature, I would think that the 0w oil would flow better...? I have driven my car about 25k miles changing the oil, using only Amsoil 0w30 & Amsoil oil filters. It's been through a 100+ degree Texas summer. The car is running great from what I can tell.
Last edited by dmoneychris; 01-08-2016 at 10:54 AM.
01-09-2016, 08:49 AM
#9
Race Director
My car is a 2013 GS w/the Dry sump LS3. Lots of oil to get moving.
This is just my thought on the matter...I've heard that most engine wear in a cold/hot cycle of an engine will happen when you first start it up. So as the engine is getting up to operating temperature, I would think that the 0w oil would flow better...? I have driven my car about 25k miles changing the oil, using only Amsoil 0w30 & Amsoil oil filters. It's been through a 100+ degree Texas summer. The car is running great from what I can tell.
This is just my thought on the matter...I've heard that most engine wear in a cold/hot cycle of an engine will happen when you first start it up. So as the engine is getting up to operating temperature, I would think that the 0w oil would flow better...? I have driven my car about 25k miles changing the oil, using only Amsoil 0w30 & Amsoil oil filters. It's been through a 100+ degree Texas summer. The car is running great from what I can tell.
I am endorsing the GM recommendation of 5w-30 and using this process outlined by the author of this thread:
The best way to protect your engine, when dealing with thick, poor flowing, cold oil, is simple. If you run an engine too hard when it’s stone-cold, you can cause unnecessary wear or even damage, due to the reduced oil flow rate/lubrication. But, all you have to do to avoid that problem, and to protect your engine, is to run it easy (small throttle openings and low rpm) for the 10 or 15 minutes it takes for it to reach normal operating temperature. All you need is a little patience, and then you can run it hard without any concern about lubrication.
I have always used this start up procedure starting with my first motorcycle back in 1964. Maybe one of the only smart things I did when younger.
Again not disagreeing with you just want others to have the information to make own decision.
Last edited by Boomer111; 01-09-2016 at 08:51 AM.
