My car has over 100,000 miles. The first 99,000 were very hard. A car guy whom I respected dearly named Neil, suggested I switched to 10w30 oil from 5w30. He was a long time car builder and racer, (Grey Ghost). Some people have warned me this could be harmful? It makes since to me to go with a 'thicker' oil with greater viscosity as the engine gets older, but allot of things make since to me and after I try them I regret it... Like marriage and those last 2 cookies I just ate. So I would like to know definitively before I go ahead and put that 10w30 synthetic in. Or maybe a blend of 10w30 and 5w...

 

As long as your temperatures stay above 0 F the 10-30 oil should be fine. As should the 5-30 oil. It should make no difference to your engine or your oil consumption.

 

Within a few minutes after starting your engine, a 10w-30 isn't going to be any "thicker" than 5w-30.

5w-30 would be better if you park your car outside in the winter and started it.
In the summer, it won't make any difference.

 

You would need to bump to 10W-40 to accomplish what he is suggesting. It probably won't matter much if you are burning oil or are losing compression.

 

My temp is always "above 0' F". I am concerned because my oil pressure does dip down low and flash's up red. I hope this will address this condition as well.

 

It has 100k hard miles its not going to make any difference either way.

Just drive and enjoy for now.

 

Here is an interesting read posted on another forum re higher viscosity oils. Some things I had never thought about.

Cliff Notes: Thicker oil may offer less protection in bearings.
So what's this FAQ about?
There's a lot of misconceptions surrounding oil. A lot of people, including people who really should know better, get a lot of the basic science behind oil and lubrication wrong. This FAQ is an attempt to arm the lay person with the basic ideas needed to understand how oil and their engine work together. Because this is written for the lay person, I'm going to explain some things in ways that'll make lubrication engineers froth at the mouth because, while it'll ignore some important details, the description will give a person who just wants to understand their car a little better the correct mental picture of how things work.

What isn't this FAQ about?
I'm not going to tell you which oil you should be running and I'm not going to tell you which oil pump is best. I'm going to tell you how to pick the best oil for you and how to pick the best mods to your oiling system for your goals.

What are the basic concepts that have to be understood?
The most important concepts to understand are viscosity, pressure, restriction, and flow.

In layman's terms, viscosity is "thickness". I'm going to use a milkeshake analogy repeatedly throughout this FAQ and it starts here. Think of a really cold milkshake made with lots of ice cream. That sucker is think. If you knock the cup over, it barely slumps down, and forget about sucking it up through a straw, you'll just turn your face inside out. That's high viscosity. Now, leave that same milkshake in the sun in the summer for an hour. It'll be all watery and runny. Knock over the cup and it'll come splashing out and you can easily suck it through a straw. That's low viscosity.

Pressure is an easy one. Most people's understanding of pressure is dead right. In our milkshake analogy, pressure is how hard you're sucking. Suck hard, you get more milkshake. Suck like a sissy and nothing comes out. However, there's a detail about the word "pressure" that we're going to cover later on and it's where about half the misunderstandings related to oil pump choice come from.

Flow is another one that most people understand intuitively. High flow is more milkshake in less time. Low flow is less milkshake in a longer time.

Restriction is one almost no one remembers to think about. In the milkshake model, restriction is the size of the straw you're using. If you think about it, it's easier to suck a milkshake through a big straw than a swizzle stick. The big straw is a minimal restriction. The little swizzle stick is a significant restriction.

How do those concepts relate to each other?
This is where the real truth starts to get complicated and to cover it as well as a college class I'd have to put in so many details that no one would ever finish reading. So those of you that know better, just skip ahead so your brain doesn't explode.

Roughly speaking, you can trade any one of the 4 basic factors for any of the other four. Think of flow as the result on the left side of an equals sign. Restriction, pressure, and viscosity go on the right side of the equals sign. Expressed in terms of flow (in the end, flow is the only thing that matters), here are the basic relationships:

If you increase the restriction, flow goes down (If you decrease the restriction, flow goes up)
If you increase the viscosity, flow goes down (if you decrease the viscosity, flow goes up)
If you decrease the pressure, flow goes down (if you increase the pressure, flow goes up)

Now, I'm going to express the idea in terms of pressure as well because it'll be helpful later on to understand why some of the ideas people have about how oil works are so wrong:

If you increase the restriction, pressure goes up (If you decrease the restriction, pressure goes down)
If you increase the viscosity, pressure goes up (if you decrease the viscosity, pressure goes down)
If you increase the flow, pressure goes up (if you decrease the flow, pressure goes down

Got it? If in doubt, scroll back up here and re-read this if you start to get confused.

Why is flow the most important thing when everyone keeps talking about pressure on NASTYSHACK?
I mentioned earlier that there's two kinds of pressure and people confuse the two (actually, they conflate them but no one knows what that means). There's pressure in the sense we typically think of it as in "water pressure", "oil pressure", or "boost pressure". That figure is almost, but not quite, totally irrelevant when talking about an oil system. There's a different thing called "separation pressure" that's one of the two most important things when it comes to oiling your engine.

Separation pressure is something almost no one understands because we never have to deal with it on a daily basis. Separation pressure is created by a fluid flowing between two objects. Flowing is the absolutely critical thing here. We have to drop the milkshake here for a moment and pick up a garden hose. Imagine a hose with a nozzle that produces a perfect jet of clear water (not a frothy white jet like most cheap nozzles). The pressure, mid air, in that jet is 0PSIg. Now, take your thumb and finger and try to pinch them together with the point they meet right in the center of the stream. The water will try to push your finger and thumb apart even though the water itself is at 0PSIg (no pressure). The water flowing between your thumb and finger exerts a force that acts to keep your thumb and finger from touching. This force is called the separation pressure and it comes solely from the flow of the water between your finger and thumb.

Separation pressure is what makes the bearings in your engine work. Oil pressure, created by the pump, sends oil flow to your bearing clearances. The flow through the bearing clearances causes separation pressure. The separation pressure prevents metal on metal contact and blocks the bearings' ability to get a non-resident visa in the oil pan. Oil pressure is only relevant to this discussion in that it's the thing that effects flow. Think of oil pressure like Mr. Brown. He (oil pressure) delivers little boxes of flow to your bearing clearances. After that, he's out of the picture. It's those little boxes of flow that cause separation pressure and keep your engine from gargling silverware.

By the way, for those of you who don't read XKCD, that's a grammatically correct use of "effects" back there.

After flow (which really means separation pressure), what's the next most important characteristic of oil?
Viscosity, but not the way you think.

What is Kinematic Viscosity
The viscosity that we're all familiar with is called Kinematic Viscosity. This is the thickness of the milkshake in the analogy I've been using. Basically, KV is how fast oil will drip out the bottom of a cup with a hole in it. Simple measurement, been around for hundreds of years. The unit of measurement is the Centi-Stoke (cSt). The "weight" of the oil is determined by the KV. So 5w20 has a lower KV than a 10W40. KV is important because it determines things like how easy it is to pump the oil up the filler tube and how quickly the oil will run back out of the engine and into the sump so it can be used again. KV (oil weight) has basically nothing to do with protecting your engine!

What is High Temperature, High Shear Viscosity
Automotive scientists were pissed off when they noticed that they couldn't predict how well a given oil weight would protect an engine. Sure, in general, they could say that heavier weights protected better, but they couldn't actually predict that Weight X would produce 5% less wear than Weight Y. This is the sort of thing that drives scientists nuts. Eventually, someone realized that a cup with a hole in it has almost no resemblance to the inside of your engine. In a bearing, it's very hot (hence the High Temperature). In a bearing, the two sides are "shearing" past each other rapidly (hence the High Shear). When they designed a test the measure the HTHS viscosity, they found that HTHS Viscosity wasn't predictable from the KV. Sure, in general, higher KV oils had a higher HTHS, but you couldn't predict one from the other. Sound familiar? It did to the scientists. So the next thing that happened is that many, many engines were run to death on oils with different HTHS and different KV. The results were hugely important. There was a very strong correlation between HTHS and the amount of engine wear. Higher HTHS oils always produced less engine wear. In other words, the most important characteristic of an oil for protecting your engine is the HTHS viscosity.

How does this relate to picking an oil?
Obviously, from what I just said, HTHS viscosity is the most important characteristic about an oil for protecting your engine. You want it to be as high as you can without running into other problems (yes, too high is potentially bad). On the other hand, since HTHS and KV sometimes trend in the same direction, this can be a problem. Ideally, you want the lowest KV you can get. Lower KV means that the oil is easier to pump and returns to the pan faster. So, to put the two together, you want the highest HTHS with the lowest KV.

Does this imply anything about synthetic vs dino?
Only in a round about way. Cheap, non-hydrocracked mineral oils tend to have very low HTHS, pretty much regardless of what the KV is. You can rule this out because the HTHS is so low, you shouldn't bother with them. Hydrocracked mineral oils (these are legally "synthetic", but there's nothing synthetic about them) like Mobil1, Pennzoil Pure Platinum, etc are slightly better. They have a moderately higher HTHS for a given KV. "True" synthetics, meaning ones not based on oil pulled from the ground have a dramatically higher HTHS for a given KV than any other form of oil. This is why synthetics used to be marked as allowing you to "run a grade lower" than a traditional oil. Their HTHS to KV ratio is so much better that they got the same HTHS out of a lower weight oil. So, if the highest HTHS for the lowest KV is what you want, Lab-grown synthetics are top of the class.

Why do race cars use heavier weight oils then?
Well, there's several possibilities. First, they may be going to a heavier KV oil to get the HTHS that they feel they need if that HTHS isn't available in a lighter oil. This isn't very likely given the good oils available today. Second, they could be behind the curve and not know that HTHS is the important thing and are just following the "conventional wisdom" that heavier oils protect better. This is highly unlikely at the top levels of racing but pretty common at the low-end grass roots stuff. The final, and most likely possibility, is operating temperature. Most engines are designed to function with a KV at operating temperature of about 10cSt. I have no idea why 10cSt is the magic number, but it is. Now, the reason this affects race teams is heat. Race engines, generally, run hotter than street engines. Heat makes oil thin out. So as the engine heats up, the oil drops below that 10cSt magic number. Heavier oils hit the 10cSt magic number at a higher temperature than a lighter oil. So some race teams, if they're finding their oil temps run, say, 20F hotter than stock, may switch up to a heavier oil to get back to a 10cSt KV at race temperature. Of course, then Billy Bobb down at the Honda meet hears that the race teams are running 20W60 and so he starts doing it in his car. I think that's where a lot of oil BS comes from.

Should I use a heavier weight oil?
Probably not. However, you'd be the exception to the rule if you did something with the car that consistently elevated your oil temperatures. For instance, if your car is a track queen and sees oil temps of 250F for an hour at a time, then, yes, you probably should run a heavier oil. If you're mostly a street driver that just sees a quick oil temp spike up to 250F when someone needs taught a lesson, no, you probably shouldn't use a heavier oil.

But heavier weight oils give me a higher oil pressure and everyone knows that's good!
No, it's not that simple. Higher separation pressure is good. Separation pressure doesn't come from higher oil pressure, it comes from higher flow. When you switch to a higher weight oil, you're actually getting LESS flow, not more. Think about the milkshake analogy. If you stick the milkshake in the freezer and make it really a lot thicker, are you getting more or less out of the straw when you suck on it? Oil is the same way. Heavier weight oils result in less flow and that reduces the separation pressure even though the oil pressure has risen.

Well, ok, if I can't use heavier oil to get more protection, then I should use a bigger pump, right?
Again, it's not even close to that simple.

First, we have to talk about the oil pump for a moment. The oil pump uses a gear with rounded teeth called the rotor to pump oil. The thickness of the rotor determines how much oil (volume) it moves per revolution of the pump. When you hear people talking about 7mm, 9mm, 12mm oil pumps, they're talking about the thickness of the rotor. Thicker rotors pump more oil so a 12mm pump outputs more oil than a 7mm pump per revolution.

Our oil pumps do something weird that most people don't intuitively understand. Our oil pumps are Positive Displacement pumps. A PD pump is a specific kind of pump that always outputs a specific volume per turn, no matter what. So one turn of the oil pump will put out, say, 10cc of oil and the pump will do whatever it takes to make that happen. "Whatever it takes", in this case, is increasing the pressure. So the oil pump turns and X amount of oil comes out. If the pump is turning slowly, that X amount of oil then has a lot of time to trickle out the bearing clearances. So the overall flow is low. Now, lets turn the pump a whole lot faster. It's still outputting X amount of oil per turn, but it's making turns a lot more frequently. As a consequence, the flow through the bearing clearances is a lot higher. So we increased flow, didn't change the oil viscosity, and didn't change the bearing clearances. The only thing that can change to balance the equation is the pressure. So turning the pump faster forces the pressure to rise because that's the only way to drive a higher flow rate through the bearing clearances. The faster you turn the pump, the higher the pressure is going to rise. In fact, a PD pump can and will cause giant castings like engine blocks to shatter if there's not some safety relief built in. Our oil pumps do have a safety relief built in in the form of a bypass valve. When the oil pressure rises too high, the bypass valve opens and the output of the pump is connected to the input. Effectively, the pump is allowed to pump oil in a circle rather than forcing it into the engine block. This caps the system pressure and prevents annoying things like shooting the cam seals out through the radiator. The key thing to realize, though, is that once the bypass valve opens and the pressure stops rising, you're not getting a drop more oil through the engine no matter how much bigger you make the pump or how much faster you turn it.

Now, lets say you switch from a 9mm oil pump to a 12mm oil pump. That means that the 12mm is going to output more oil (have a higher flow) at a lower speed than the 9mm pump. If the pump was the only thing you changed, all that's going to happen is that the oil pressure increases more rapidly, you reach bypass pressure sooner, and not a single drop more oil is forced through the engine.

Why the heck do engine builders recommend upgraded oil pumps then?
Remember how I just said "if you change the pump and nothing else"? Your built engine almost certainly changed "something else". Almost all built motors run wide bearing clearances to allow for heat expansion and for higher flow to get increased separation pressure to cope with the big power. Increasing the bearing clearance reduces the restriction just like going to a bigger straw. This means that the pump has to pump more oil to "fill" the bearing clearance and keep the separation pressure up. So you have to have a bigger oil pump to get enough oil to your big bearing clearances. Similarly, if you take an engine that didn't have a turbo, or didn't have single/dual AVCS and add those systems, the oil requirements are going to increase, demanding a bigger pump. Basically, you need to match the pump to how "thirsty" the engine is. If you made the engine want more oil, get a bigger pump. If you didn't make the engine want more oil, don't change the pump.

 

Kid, that engine can't tell the difference between 5-30 and 10-30.

 

After reading George4's attachment - I am wondering if the issue could be with my oil pump since it is responsible for that pressure. How can I tell? Thanks for the post George4.

 

Its more likely to be your bearing clearances are bigger and so less pressure.

 

This is more likely the case. The olalaska dude just posted about refreshing the bottom end as soon as you notice pressure drop and well before it starts to knock. The bearings are not that expensive, labor probly so. The process isnt terribly hard, just be careful and dont scratch the crank journals and torque carefully to spec.

Good luck!

 

I will always keep 5W-30 in my vette

 

That's not good, you've got a engine that isn't doing well and changing oil to something thicker isn't going to help.

 

i will check out the bearings but that engine was rebuilt less than 5k miles ago

 

Thanks for the Very informative & insight on oils, bearing clearances, oil pumps, ect.

I never have been a fan of setting Up V8 engines on the loose side with .003"-.004" + main & rod bearing clearnces during shortblock build ups & having to run 50w, 60w or 80 w straight viscosity motor oils.

90 % of the time an average street guy & racer should never need more than .002" on the main & rod bearings for running oil clearance during engine buildup.
Melling standard or HV pump is more than enough flow.
And 10w30 oil will be just fine.

Pontiacs I have to run 100psi hot oil pressure at 4,000RPM's & 120psi hot pressure at 6K rpm's.

10w30 oil I run.

turn them high as 8K +.

Many oil mods have to be done to a Pontiac to keep them together like I run them.

Unlike a Chevy sbc or bbc.

BR

 

eeehhh...miles don't matter. build quality does.

set aside about 4hrs one day and yank that motor. top end/accessories pop off in a couple hours. take a beer break. disconnect wiring, loosen torque converter/bellhousing/motor mount bolts, yank motor out. take beer break.

anymore i trust no one but myself in this area (16701 zipcode). i'd tear it down and carefully mark everything and blueprint it as it goes back together. new pump/bearings/seals/gaskets/bolts/cap/rotor/wires/hoses/etc and double & triple check your work. a basic rebuild should set you back no more than 400 bucks (beer included) and you know it was done right.

I'd also suggest drinking no more than 6 beers per break. just sayin. not that i'd know or anything

 

A 12 - pack of beer in you &

And you will have an easier time reading the plastic gauge & Starret micrometers just fine checking the crankshaft running oil clearances.........

BR

 

My 87 Corvette has its original engine, never overhauled and it has 239,000 miles on it and has always had 10W30 oil in the crankcase! Oil pressure is normal too!

 

One question is what year motor?
If its a 86e or earlier, you should be running a zinc additive for lubing the flat tappet lifters. Otherwise.....never mind.

 

I think everyone forgets that all the factory specs are aimed at fleet milage and passing a smog test. do you really think they wanted to fool with that 4+3 mess rather than just have a 4speed. They are equally smart to know that for decades 192 degree engines last just fine and nothing to gain by going hotter other than ppm smog stuff. What would make you think oil is different? Before smog ***** everything ran 10-30 for normal use and 20-50 for severe duty whatever that is. If driving like an old woman I am definately severe duty..LOL and yes run 20-50 and don't drive the car on days below about 45 degrees. Change it often is probably the best oil advise anyone could give.
Dave