Overheating Z-28 I'm Stumped?

I have a 96 Z-28 LT-1 5.8L That I have been given that task of finishing. The car was totaled (Front End) and been restored to original order other than the overheating problem that was not their before the restore. The motor was never removed. simply replaced the rad, fans, fenders, hood ect.

Extensive testing on the systems have shown that the cooling fans and fan relays operate correctly. The temperature read by the computer is correct as far as what it reads on the dash panel and the temp of the fan triggering sequence for all three fans. The temp sensor on the front end of the motor that triggers the cooling fans has been replaced to verify that it is in order since the damage was to the front end of the car, The wire lead to the temp sensor was replaced to insure no lack of proper signal to the computer. There there are no leaks and the radiator and thermostat have been replaced. The water pump in in normal working order (as far as I can tell with out removal)

The procedure that I am using to fill and bleed air from the cooling system is as follows. I have the front end on jack stands. With the cap off the radiator and the bleeder valve cracked open. wile it runs till the thermostat opens (if it does not start to overflow/steam to much) and tighten the bleeder valve and replace the cap.

When I run I get a steady flow of air/coolant mix from the steam pipe/throttle body flow to the radiator to the extent that it never stops eventually creating such an overflow problem that it fills the overflow to the point of overflow past the cap and then overheats totally as a result of the slow loss of coolant. The first fan tends to operate a bit late but not more than 5 deg.

Some of my last thoughts are that there is a blockage somewhere in the heads, passably trying a 160 deg. thermostat to cool it off a bit earlier or I have been unknowingly unable to remove all the air from the system after many attempts. Maybe I simply need a Prozak refill and a beer.

Any thought or suggestion regardless scope or nature is welcome.

Thanks, Ziggy

These cars like to get debris in that space in front of the radiator. You don’t mention a time frame or driving conditions that are involved with the overheat. Maybe there is bodyshop paper stuck in front of the radiator.

The driving conditions are that it is in park and not on the road. It bubbles over befor you can even get the cooling system filled. This condition starts from start up cold before the themostat opens and continues after it opens.

I wonder if you have a combustion leak to the coolant jacket. Do you have access to a hydrocarbon sniffer to check at the rad neck?

You are dead on. This type of overheating is caused by exaust gases comming in contact with the coolant,am I 100% sure? no but it fits.

Do you think that an impact to the motor compartment may have shaken up or possibly jogged the manifold causing this problem? The car spent the winter in eastern Washington out of my view. Perhaps the coolant mix was off and there was some freezing in that area?


Could The Engine Have Been Run Long Enough After The Crash To Have Overheated It?

Was it driven at all (w/ broken radiator) after the accident or was that not possible?

The car came to me after being put back together and in running order other than the overheating prob. When I got it it had a pin hole in one of the main rad hoses and was very low on coolant. I was told that it was overheating for no reason. I have no idea how long it ran or how hot it got other than after I got it. I do know that it has been ran long enough to caws minor combustion and or running problems for 1-2 min. by the owner (My sister in law)


You can check for hydrocarbons in the coolant by using this kit. http://www.automotive-diagnostic-tools.com/Head-Gasket-Leak-Detector-Kit-p/uv%20560000.htm


You Should Pressure Test The Cooling System With A Pressure Tester.

I have one made by Stant that I’ve had for years. The system needs to hold pressure or you’ve got a leak(s). This car could have head gasket problems or worse. If you don’t have the tester, you might be able to borrow one from an auto parts store. Advance Auto loans tool kits, but I don’t know if this is one they provide. I can’t speak for the other chain parts stores, either. If it won’t hold pressure and is losing coolant and it’s not leaking externally, then it’s leaking internally.

Oooo, I Like It. Have You Ever Heard Of Using Test Strips Made For Doing This?

Do they work?

OK well after speaking to a senior tec at a local dealer along with all the help from all of you it does sound like all it could be is a bad head gasket. That would help explain the slightly noticeable miss at idle speed. I can get a pressure tester no prob. Even though it does sound cut and dry, bad head or gasket? if I find anything other than that I will post it. Thank you for all the help.


Thanks For The Update. Good Luck.