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Last week it was near 90 in Detroit and I noticed the temps creeping up to 230-240ish when sitting in traffic. Checked fuses and fans and all seem to be working. where does this rubber block go?
I've only owned this car for a year and read on this forum about cleaning out the debris under the fan shroud. It was about 1/3 blocked, so I removed the air cleaner and shroud and cleaned everything. Seems to be running much cooler now. Anyway this piece of rubber fell off while removing. Does anyone know where it goes?
I think 230°, while the car is not moving is normal. 240 is too hot. GM set fans to come on at a very high temp when idling to try to reduce emissions. Idling engine is a dirty engine. That's the only rationale I can think about running them so hot at idle. All of my late model vehicles do that.
Pressuring the coolant raises the boiling point. It is an easy and very low cost way to add a few degrees before your engine will overheat. The downside is that it increases the stress on all the cooling system components (hoses, coolant reservoir tank, and heat exchangers). Every time you start your engine and it has warmed up, it will pressurize your system to 18 psig rather than 15psig. For me, I will not replace my 15 psig cap on my '99. There have never been circumstances here in SW Ohio where I ever come anywhere close to over heating.
Pressuring the coolant raises the boiling point. It is an easy and very low cost way to add a few degrees before your engine will overheat. The downside is that it increases the stress on all the cooling system components (hoses, coolant reservoir tank, and heat exchangers). Every time you start your engine and it has warmed up, it will pressurize your system to 18 psig rather than 15psig. For me, I will not replace my 15 psig cap on my '99. There have never been circumstances here in SW Ohio where I ever come anywhere close to over heating.
It is not necessarily true that every time his engine is warmed up that it will now have pressurized the coolant to 18psi rather than 15psi. The cap rating doesn't generate pressure! Whatever pressure he had before, he will still have. The higher rated cap will raise the boiling point of the coolant, nothing more, nothing less. If he wasn't boiling before, and he shouldn't have been, it will do nothing for him except add a little insurance against getting scalded if the 15psi cap couldn't hold the pressure.
It is not necessarily true that every time his engine is warmed up that it will now have pressurized the coolant to 18psi rather than 15psi. The cap rating doesn't generate pressure! Whatever pressure he had before, he will still have. The higher rated cap will raise the boiling point of the coolant, nothing more, nothing less. If he wasn't boiling before, and he shouldn't have been, it will do nothing for him except add a little insurance against getting scalded if the 15psi cap couldn't hold the pressure.
Let me see if I can clarify by use of an example with the simpler coolant overflow bottle systems used commonly in automotive. The principal is the same as in our C5 flow through reservoir systems but easier to describe with the overflow bottle.
A cool engine starts at about 0 pisg. and the coolant bottle insures that the radiator is full of coolant This low pressure is easy to feel by squeezing the cool radiator hose. There is a little resistance but not much because your hose squeeze only reduces the system volume by a little bit; it builds a little pressure but not much. Now take off the radiator cap and squeeze it again.......what happens is you will see coolant burp out of the radiator. The amount that burps is approximately the same as the volume you reduced by squeezing the hose. Coolant did not burp out of the overflow with the cap on because that small change in system volume was insufficient to exceed the radiator cap pressure. While you have the hood open, note also the level of the coolant in the overflow bottle. Hopefully it is at either the "fill cold" or the "low" line. Now start the engine and drive somewhere to allow the coolant to heat up. Then stop the car and look at the coolant bottle, lit will now be above the cold fluid level. The coolant volume expands as the coolant heats up. The higher the coolant temperature, the higher its rate of thermal expansion and increase in coolant volume. Now when you try to squeeze that hot radiator hose it is much more difficult to do. As the coolant volume increases, it raises the pressure within the cooling system, applying stress to expand everything it can; hoses, radiator and heater plastic tanks, even the radiator and heater tubes. The radiator cap holds back that pressure as long as it can until it vents that hot high pressure coolant into the overflow bottle. If the cap is 15 psig, it will vent the hot coolant to the overflow bottle to maintain a maximum radiator pressure of 15 psig. If an 18 psig cap, it will maintain an 18 psig maximum radiator pressure. This example holds true anytime you heat the coolant sufficiently to need the radiator for cooling and you have a full coolant system. On a 30 or 40 degree day, maybe that coolant bottle level won't change much and you won't hit cap pressure. On a 70, 80, 90 degree day...... you certainly will see that level rise and will be operating at cap pressure. The hotter the coolant gets, the more it will burp out to the overflow bottle to maintain the radiator at the cap pressure.
Bottom line, an 18 psig cap will pressure cycle the cooling system components at a higher pressure than a 15 psig cap.
Bottom line, an 18 psig cap will pressure cycle the cooling system components at a higher pressure than a 15 psig cap.
No it will not. The pressure in the system is determined by the amount of coolant, air, and temperature. A radiator cap affects none of those factors.
What radiator cap is installed only determines the boiling point and maximum pressure before venting.
Read the DeWitt's article posted earlier.
If you're not boiling the coolant with the 15 lb cap you're not getting any higher pressure than that and it's irrelevant what cap you put on it.
No it will not. The pressure in the system is determined by the amount of coolant, air, and temperature. A radiator cap affects none of those factors.
What radiator cap is installed only determines the boiling point and maximum pressure before venting.
Read the DeWitt's article posted earlier.
If you're not boiling the coolant with the 15 lb cap you're not getting any higher pressure than that and it's irrelevant what cap you put on it.
Let me further clarify Dads2kconvertible. Let's stick with the simpler and very common example of an automotive cooling system with an overflow bottle. A correctly functioning coolant system does not contain any significant quantity of air. It is full of coolant without any significant air space. Whatever small air space there is will get pushed out as soon as the system reaches operating temperature (thermostat open, and pressure due to the expanded volume of the coolant. To prove that, there is not air in the system, take the radiator cap off a cool system and you should see coolant right up to the top of the radiator tank where it meets the pressure cap seal. It maintains a full system because the overflow bottle captures the coolant that burps out as the cooling system heats up in normal operation and allows the coolant to flow back in as the system cools and creates a vacuum.
The heated coolant expands with temperature while the volume of the system is constant except for the deformation of the plastic and rubber components, and to a very small extent, the deformation of the heater and radiator tubes. For practical purposes, the volume of the coolant system is fixed. As the coolant volume increases with every degree of increase in temperature, the pressure has to increase as well because the coolant is incompressible. Whether the coolant is at 160, 192, or 265 degrees, it will expand and continue to expand in volume as it heats. As it expands, it has nowhere to go but out into oveflow bottle as the cap works to maintain its 15 or 18 psig set point. The only thing the pressure cap does is regulate the pressure in the cooling system.
The Dewitt's article actually raises the same caution that I have raised but without the technical explanation of why: From DeWitts - "So, you may be asking yourself why not just install a higher rated radiator cap at 18 or even 21 psi? While yes, this would raise the boiling point further, the extra pressure places a tremendous amount of strain on the rest of the cooling system. You must remember it isn’t just the cap we’re talking about here, but the complete system. Cooling hoses, your heater core, water pump gaskets/seals, and more all become stressed at these higher pressures, which is why we prefer and only sell radiator caps rated at 15 psi for our radiators."
Now I have my own theories as to why GM and Delphi raised the cap pressure from 15 to 18 psig.
Theory 1: From what I can tell, they reduced the size of the a/c orifice tube somewhere in the 1999 or 2000 model year. The standard orifice tube is an 0.072" diameter and they went to something like an 0.067" or 0.063". I am quite sure they would have done this to get improved a/c cooling in high ambient extended idle conditions. This improved performance with a smaller orifice tube comes at a price of higher condenser temperature and subsequent higher radiator inlet air temperature. Higher radiator inlet air temperature leads to higher coolant temperature when the thermostat is open. GM/Delphi have various performance requirements under high ambient conditions and one of them is no overheating for a minimum of 30 minutes in Las Vegas like extended idle city traffic conditions.
Theory 2: GM/Delphi found they were receiving overheating complaints in export markets like the Middle East where 120 degree ambient high speed and 120 degree city traffic/extended idling is common. Do they invest mid way through the C5 life cycle in more powerful fans, a bigger alternator to support the fans, a higher heat transfer radiator? Sounds like a lot of R&D and cost. So perhaps they took the quick easy way to get a few more degrees before boiling by increasing the radiator operating pressure.
For whatever reason GM/Delphi chose to raise the cap pressure, I am quite sure they had solid design verification evidence to support reliability and durability at the higher pressure. If I had a later C5 that came with a 18 psig cap would I change it to the 15? No, I would not bother. If my 15 psig cap on my '99 goes bad tomorrow, will I replace it with a 15 psig? Sure I will if they are available. My car will never see driving conditions that will require a higher boiling point.so why subject it to higher pressures.
My car will never see driving conditions that will require a higher boiling point.so why subject it to higher pressures.
The pressure at any given temp is NOT dependent on what radiator cap you're using.
If you're at 260 degrees you're at pressure X whether you have a 15 lb cap or a 225 lb cap.
Maybe try thinking about it this way @bookyoh What temperature do you think your system reaches 15 lbs of pressure? Now same thought experiment, what temperature does it reach 18 lbs of pressure?
Imagine your radiator cap was replaced with a 999,999,999,999,999 lb cap. What temperature would you reach that pressure?
Last edited by Dads2kconvertible; Jun 6, 2023 at 09:13 AM.
The pressure at any given temp is NOT dependent on what radiator cap you're using.
If you're at 260 degrees you're at pressure X whether you have a 15 lb cap or a 225 lb cap.
Maybe try thinking about it this way @bookyoh What temperature do you think your system reaches 15 lbs of pressure? Now same thought experiment, what temperature does it reach 18 lbs of pressure?
Imagine your radiator cap was replaced with a 999,999,999,999,999 lb cap. What temperature would you reach that pressure?
I am not goimg to debate physics with you Dads2kconvertible but I will leave you with a simple experiment to illustrate that the radiator cap regulates the system pressure at any temperature. Here is the experiment:
Go out to one of your vehicles with a simple lverflow bottle cooling system that has beem sitting long enough so the coolant is at ambient temperature.
Take a piece of tape and mark the coolant level on the overflow tank.
Start the car and let it idle for 10 minutes later and note the level of the coolant in the bottle.. Has the level risen? Squeeze the radiator hose; does it feel like it is under pressure?
Let it idle another 10 minutes. By now the vehicle should certainly be under thermostat control but nowhere close to overheating. What is the colant level in the oveflow bottle compared to the cold level ? Has it risen?
What this illustrates is the thermal expansion of the warming coolant and that is can expand sufficiently to burp out coolant while operating under normal thermost control, The poit at which it burps is determined by the radiator cap pressure setting.
The coolant level rises because the radiator cap opens sufficiently to release enough warming coolant to keep the radiator at the cap pressure. It does not matter if it is 160 degrees or 260 degrees. The cap responds to pressure as the coolant volume expands as it is heated. Temperature is what raises the pressure of the coolant because the volume of coolant grows via thermal expansion but it is trapped within what is essentially a fixed coolant system volume. As the cooant volume grows, the pressure rises, and the cap regulates the maximum pressure regardless of the coolant temperture.
I think I see what you're saying now. You think the system reaches 15 lbs well below the boiling point of the coolant.
I'll have to give that some more thought, you might be right.
Thanks for the discussion.
Let me see if I can clarify by use of an example with the simpler coolant overflow bottle systems used commonly in automotive. The principal is the same as in our C5 flow through reservoir systems but easier to describe with the overflow bottle.
A cool engine starts at about 0 pisg. and the coolant bottle insures that the radiator is full of coolant This low pressure is easy to feel by squeezing the cool radiator hose. There is a little resistance but not much because your hose squeeze only reduces the system volume by a little bit; it builds a little pressure but not much. Now take off the radiator cap and squeeze it again.......what happens is you will see coolant burp out of the radiator. The amount that burps is approximately the same as the volume you reduced by squeezing the hose. Coolant did not burp out of the overflow with the cap on because that small change in system volume was insufficient to exceed the radiator cap pressure. While you have the hood open, note also the level of the coolant in the overflow bottle. Hopefully it is at either the "fill cold" or the "low" line. Now start the engine and drive somewhere to allow the coolant to heat up. Then stop the car and look at the coolant bottle, lit will now be above the cold fluid level. The coolant volume expands as the coolant heats up. The higher the coolant temperature, the higher its rate of thermal expansion and increase in coolant volume. Now when you try to squeeze that hot radiator hose it is much more difficult to do. As the coolant volume increases, it raises the pressure within the cooling system, applying stress to expand everything it can; hoses, radiator and heater plastic tanks, even the radiator and heater tubes. The radiator cap holds back that pressure as long as it can until it vents that hot high pressure coolant into the overflow bottle. If the cap is 15 psig, it will vent the hot coolant to the overflow bottle to maintain a maximum radiator pressure of 15 psig. If an 18 psig cap, it will maintain an 18 psig maximum radiator pressure. This example holds true anytime you heat the coolant sufficiently to need the radiator for cooling and you have a full coolant system. On a 30 or 40 degree day, maybe that coolant bottle level won't change much and you won't hit cap pressure. On a 70, 80, 90 degree day...... you certainly will see that level rise and will be operating at cap pressure. The hotter the coolant gets, the more it will burp out to the overflow bottle to maintain the radiator at the cap pressure.
Bottom line, an 18 psig cap will pressure cycle the cooling system components at a higher pressure than a 15 psig cap.
You MAY be correct IF the C5 had an actual radiator cap, which it does NOT, and IF the system was boiling over with a 15lb cap. So, you are incorrect on your assumption. The only thing that raises pressure is more heat! If he ran at 215°F before, he will still run at 215° now, with the same pressure as before. He could put a 60lb cap on the reservoir, and it doesn't mean he will now have 59psi pressure. Cap ratings mean there'll be no leakage until the caps rating is met, or exceeded. Again, CAPS DO NOT MAKE PRESSURE. Just because a car has W rated tires (good to 168mph) does NOT mean the car will go faster if you install Y rated tires (good to 186mph). You are basically saying the same thing! An 18 psi cap does nothing more than offer a 3psi increase in boil over/pressure in the cooling system. You actually proved yourself wrong with your "simple" theory about why GM changed the cap from 15 to 18. If the A/C orifice tube change made the condenser run hotter, as you say, then that would create higher coolant temps, which equal more pressure in the cooling system. They were adding a 3lb increase in boilover protection, due to the possibility of the coolant temp rising higher than before. By the way, you're not the only one here who has had physics classes. I'll take your "simple" explanations as just back and forth discussion, as they could be construed as a condescending manner of speech. Good discussion......
Last edited by grinder11; Jun 6, 2023 at 06:58 PM.
You MAY be correct IF the C5 had an actual radiator cap, which it does NOT, and IF the system was boiling over with a 15lb cap. So, you are incorrect on your assumption. The only thing that raises pressure is more heat! If he ran at 215°F before, he will still run at 215° now, with the same pressure as before. He could put a 60lb cap on the reservoir, and it doesn't mean he will now have 59psi pressure. Cap ratings mean there'll be no leakage until the caps rating is met, or exceeded. Again, CAPS DO NOT MAKE PRESSURE. Just because a car has W rated tires (good to 168mph) does NOT mean the car will go faster if you install Y rated tires (good to 186mph). You are basically saying the same thing! An 18 psi cap does nothing more than offer a 3psi increase in boil over/pressure in the cooling system. You actually proved yourself wrong with your "simple" theory about why GM changed the cap from 15 to 18. If the A/C orifice tube change made the condenser run hotter, as you say, then that would create higher coolant temps, which equal more pressure in the cooling system. They were adding a 3lb increase in boilover protection, due to the possibility of the coolant temp rising higher than before. By the way, you're not the only one here who has had physics classes. I'll take your "simple" explanations as just back and forth discussion, as they could be construed as a condescending manner of speech. Good discussion......
Well Grinder, I thought we had this all sorted out. With no intention of being condescending,
- I choose to use the coolant overflow bottle system to illustrate how coolant leaves the system when the engine warms up and the radiator pressure builds to the cap setting. The flow through reservoir functions in a similar way but it is easier to visualize a bottle on the side of the radiator with a coolant level that rises when hot and drops when cold.
- I wrote multiple times that it is temperature that leads to the rise in coolant pressure because coolant volume expands as the temperature increases.
- I fully agree that a 3 psi increase in maximum pressure raises the boiling point.
- I fully agree that a higher pressure cap does nothing to impact the coolant temperature. A higher pressure cap only increases the boiling temperature and it increases the maximum pressure that all the cooling system components are cycling. The components with an 18psig cap will cycle between 0 and 18 rather than between 0 and 15. Higher pressure equals higher stress on the components.
This point about pressure cycling was the point I wanted to make at the start of this. My words of caution were to just be aware that a higher pressure cap will cycle your cooling system components to higher stress. If your C5 came with a 15psig cap and you do not run it under extreme temperature loads, why switch to 18? I believe that what I am raising as a caution is the same as the DeWitt blog I quoted earlier.
Now I am 100% confident that GM and Delphi fully completed design verification of the cooling system before raising it by 3 psig so I am not trying to cast any doubt on reliability at 18 psig.
Last, and I really do want this to be the last of it, my theory about the orifice tube change is the same as you wrote. By decreasing the orifice tube diameter, the condensing pressure will increase. Higher condensing pressure for a given ambient will result in higher radiator inlet air temperature and higher coolant temperature. To delay boil over under very high ambient load conditions, my theory is they raised the maximum radiator pressure.
To delay the point where the system will boil over (and the customer becomes very unhappy), adding 3psig to the radiator pressure is a cheap way to accomplish that. Back to my example of Las Vegas like extended idle/city traffic, the GM/Harrison Radiator (pre Delphi) engine cooling performance test requirement some years ago was: 100 degree ambient at 40% humidity, vehicle up to full operating temperature at highway speed, high blower speed, outside fresh air……. Then pull up to a wall with the transmission in drive and sit there idling for 30 minutes. The requirement was no overheating for 30 minutes. Adding 3 psig will extend that time before boil over.
High temps when not moving
