C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette
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Does this look right?? Cooling system question

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Old May 23, 2025 | 03:15 PM
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Originally Posted by corvette74
I agree with the guys. Here is a pic of the overflow tank on my 74.
Hey, you Ontario people! Stop showing off!
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Old May 24, 2025 | 08:04 AM
  #22  
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From looking at the pictures it is pretty obvious what is going on in your cooling system. You have hoses that are trapping air in the cooling system. The hose that feeds the overflow can goes up higher than the thermostat housing and radiator cap. This will likely trap air or at least impede the flow of the coolant. Air traps are very common.

Most of our C3's came with the Overflow tank in the coolant lines. On the cars made without one I would install one myself, the overflow container is a crucial piece of equipment in the cooling system. On my 1968 BB C3 the tank I use is like the one in the pictures and is less than 20 years old. To make the expansion tank work you need a good set of hoses that connect the radiator cap outlet to the inlet on top of the overflow can. When the engine first starts and warms up, the coolant will expand and then overflow into the expansion tank. Then as the engine cools down the coolant will be drawn back into the radiator which brings it back to full and ready for action the next cycle. If air is pulled into the radiator instead of coolant then you will have a radiator with a big air bubble on the top of it and this will impede the flow of the coolant and make the engine run hotter. When my engine started with an air bubble in the radiator the operating temperature would go up dramatically. It is important that the radiator be full of coolant to do it's job properly. Keep your overflow working and you will keep the air out of the radiator.

Also remember that the part of the cooling system that lets your engine operate up to 261*(F) is the radiator cap, nothing more. The radiator cap should be replaced every few years as they loose the ability to hold the pressure and this allows the engine to run hotter and hotter. It is the first thing I check on a "Hot" running engine. The second is the percentage of anti-freeze, as it will make an engine run hotter if they used too much anti-freeze in the coolant mixture.

Also check for the radiator seals to be sure they are forcing all the air through the radiator. Check for the chin spoiler as well as it helps push air into the cooling system.

If your engine has an EGR assembly then it could be stuck which also causes Higher running temperatures. I would fix it to ensure it helps your engine. This issue caused my C4 to fail emissions which required a complete rebuild of the EGR system on my C4. The bad EGR causes the cylinder temperatures to rise and this leads to detonation.

No Corvette should be dumping raw coolant on the ground anymore. With the right parts on the engine the coolant level will remain constant despite the heat cycles the engine goes through. Old anti-freeze is highly toxic to small animals and household pets, it smells sweet and they drink it which in turn will kill the animal.
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