Topic: Hot at high RPM
in Forum: C3 Cooling and Heating Systems
Yes, both the lower and upper hoses have springs installed. I still do not understand why the "upper" radiator collapses at high RPM. After the car warms up, I could rev the engine and watch it suck shut before I installed the spring. What's the likelihood that I have a reverse direction water pump installed. I contacted the previous owner and he had replaced the water pump within the last year because it leaked. He never had any overheating problems before that. Humm.... I not sure how I could check to see if it's pumping the correct direction or not.
Lifetime MemberModerator
When you rev the engine up like that, it creates a vacuum in the water passages. It's caused by the pump pumping the water in quicker than letting it out. The thermostat is essentially a restriction in the system. The water going out has to go thru the thermostat, and that slows it down, but the pump is still trying to pump. So...it "sucks" on the intake side of the pump. Once there is a vacuum, something has to give, and rubber hoses being what they are, that is the give.
If the cap has the correct rating, and the overflow is not restricted, this bit of suction shouldn't really be an issue. The cap should allow the vacuum to pull coolant back out of the overflow as needed.
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
Ok, pump is not running backwards, duh. I went ahead and replaced the thermostat. This time I ‘burped’ the system afterwards. With the radiator cap off started the car and waited for the tstat to open. Upper hose began to get warm and a minute later coolant burped out the radiator cap and the coolant level dropped out of sight then came back up. I could see the tubes in the radiator and they had water flowing through them fine. My question is, how may time do I let it burp? Once or continue till it stops?
Jim Olson 
"The Toys"...!!! Save the Wave! 
Lifetime MemberModerator
A couple of times should be fine. Then put the cap on, make sure the overflow is FULL, and then drive it a while. As the engine cycles thru the temp range, it will pull the coolant it(the radiator) needs from the overflow tank. Once it no longer empties the overflow, it should be full to spec. Then, just see that the overflow tank is at the correct level for "Hot". Drain or fill as needed to get it to the "hot" level, and you're done.
If all is well, once it cools back down to cold, the level in the overflow will be up to the "Cold" mark.
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
