Several months ago, my 95 Vette with an LT1 all of a sudden overheated. Seems like one of my freeze plugs came loose, so they were replaced at a local tranny shop $650 later. The overheating problem never went away, so the thermostat and water pump were replaced. Still overheating. I then took the car to two Chevy dealers, who both together made over $1000 off me without ever finding the problem, though they supposedly cleaned the garbage between the radiator and air conditioning condensor, flushed the system out several times, replaced the thermostat again, changed the computer, and rodded out the radiator (even though it was only a year old) and still found nothing. The only thing I've been able to tell, is that I can leave the car idling for an hour in my driveway and the fans turn on and off when they're supposed to and the car will not overheat. As soon I put it in gear, it starts to overheat. I can drive the car on the freeway and it will stay cool, but if I get caught at a redlight, it overheats. Has anybody out there experienced this and is it possible that the shaft that turns the water pump inside the motor could be bad? If so, how can I diagnose this? My poor Vette has been sitting in the driveway for months because this has been a frustrating thing, especially when this happens during escrow for a house in California! Any help is appreciated!

 

Define overheat? over 228*?

It overheats under load? That's strange.

Actually, it's not strange, it's bad.

Overheating problems like this make me think there is a bad head gasket. There is a test you can perform that checks the contents of the coolant - if the coolant contains combustion gases, you have a weaping head gasket.

Another thought, a leak somewhere in the system.

A big cause is the surge tank. It's the tank on the firewall where the rad cap is. The tank can crack at the collar for the cap, when that happens, a small leak can develop and pressure is lost.

Another problem is a bad cap, it's just not holding pressure anymore. Half the success of a cooling system comes from the fact is slightly pressurized (about 2psi above atmosphere).

Has the system been pressure checked?

sounds like whomever you have taken it too in the past, has been utterly clueless... sad to say...

It over heats in gear? Automatic? If so, then the problem could be with the tranny.... or the cats... they could be clogging and causing things to get hot.

so many things...

I will tell you this: It wasn't the computer. That was a total mis-diagnosis. There is no way the computer caused this problem.

As for the shaft that turns the water pump... it is possible. it could have been damaged.

however, if there is a big problem here, it's gonna be with head gaskets - or the heads themselves (ie, cracked/warped when overheated).

 

define overheat

 

When it overheats, the needle pegs out. There's no water in the oil, and I haven't noticed any white smoke, however, it did fail the smog test, althought it passed the last time two years ago. Can this be related?

 

Also, it is an automatic. The radiator cap was replaced also.

 

What I did was wire my fans to a manual switch and turn them on manually sooner than 200

 

I had a clogged precat on my '90 L98...there was a noticeable rise in temperature. Replacing the both precats fixed that problem...you could hear the material inside rattling, it was a awful racket too.

 

I had similar problems with my mustang (v6 daily driver) after it overheated once, and the culprit was a bad head gasket. the water in the system would actually run very low and it only overheated in traffic.
i hope this is not your problem, but you may want to look in this direction.

good luck,

joel

 

I'm having the EXACTLY the same problem with my 92. I'm in the process of doing a compression test and a cylinder leak down test. I did use a test that detects exhaust gases in the coolant. This is where I got mine. http://jcsonlinetoolshed.com/product...052fa1950cf4e6

It is a good definitive test, easy to do and will confirm the presence of a problem....or not. For $30 not a bad investment.

 

I'm thinking along the same lines as bogus. Maybe u warped the head the 1st time it overheated, and now the gasket is leaking

 

This is a common sequence of events.

 

Has anyone checked the accuracy of the guage? Does it boil over?

 

While I agree it's highly unlikely, it is not "there is no way." The computer controls the fans, so it could cause overheating if it wasn't turning on the fans.

When you stop at the redlight, are the fans on?

If you let it sit in your driveway and it's fine, and then you drive around the block and put it back in the driveway and let it sit, does it overheat? Are the fans on then?

 

What part of the test did it fail?

 

the computer would throw a code if the fans could not be triggered.

it's expecting some feed back info to confirm the fans activation. I will confirm this.

 

You're assuming the computer is working correctly enough to throw a code. Since we're hypothesizing a defective computer, that's not a valid assumption.

Further, even if the code-throwing part is working right, there is data in the flash with the on and off points. If the set points were changed/corrupted then I don't think it would throw a fan code, because there's no problem with the fans for it to detect. I'm pretty sure if I reprogram my fans to come on at 280 it will happily boilover with no idiot light. I'm not going to try it however.

Finally, I've had my car boilover once when I forgot to reconnect the fans, and I did not get a check engine light, so I don't think it throws a code for fan malfunction either.

<edit> But this is pretty academic, since we both consider it was at most very unlikely to be his problem, and surely isn't his problem now since he has a new computer</edit>

 

My 96 is doing the same thing, i would be curious to know how this turns out, mine is fine until i get caught in traffic, today it was 234 deg during rush hour, i also have some coolant loss i cannot track down
Keep us posted
~B~

 

My 93 was pegging out the temp gage while in traffic, never boiled over though. I checked everything I could and still couldn't find the problem so I had to take it to the dealer. Turned out the gage was defective and showing higher temps than what it actually was.

 

good theory, but for one flaw - the EPROM stores the fan data. When a new computer is installed, the EPROM is reused.

I am still thinking a problem with either the cats (but that has been defeated by the non-overheating at idle) or the head gasket(s).

 

He still hasn't said what temperatures it hits...