1993 LT1 383 Auto

I'm having the common overheating problem. But this one is baffeling me.
It happens when the car is at a prolonged idle with the A/C. Its about 89* and humid outside (florida). It went all the way to 338* in 1-2* increments over a 15 min. period (from 196*).

So far I've blown out the debris from in front of the radiator with no luck in solving the problem. I've also checked to make sure both fans are working. I have the ECM programmed to turn the second fan on at 185* and it does. However, this isn't really relevant since the LT1 fans both turn on anyhow at any temp when the A/C is on. The waterpump is less than 2 years old and probably only has 10,000 miles on it. The radiator was also rodded out (where the clean all the gunk out of the cross fins with a poker, acid dipped, otherwise cleaned and new side tanks installed - all at the same time the water pump was changed. Also, the car has the Hypertech 160* thermostat in it (which at these temps is irrelevant). The coolant is a 50%/50% mix.. WTF?

As stated earlier the motor is a 383, with hyperutectic pistions at a 10.8:1 compression ratio. Comp Cam camshaft with spec similar to a Hot Cam (see sig). It blows when things aren't going your way!!

any ideas?

 

338????!!!??? Isn't 250 the danger zone?

At any rate, I had issues with my electric cooling fan motor. The fans would function as expected, but the reality was that the fans were not spinning up to the correct RPM and thus moving less air around. New fan motors cured this for me.

Ron

 

Take it to someone who has one of those infra-red heat detectors. Your gauge and/or sending unit might me off.

 

I hope 338 was a typo, because that'll blow a head gasket in a heartbeat.

I would have to doublecheck the gauge reading first, considering the cooling modifications you already have, then burp the cooling system one more time.

If that doesnt fix it, I would have to consider going up to a bigger radiator. I cant think of anything else it could be.

 

try running the car without the thermostat installed and put the thermostat in a pot of hot water and see if it opens.

 

Also, make sure that your antifreeze is a 50:50 mix. I used to have a mods trans Am keep getting overheat after the mods. I try everything it did not help. Then I add more antifreeze without add water. Boom the over heat if gone.


Bruce

 

check theHypertech 160* thermostat make sure it is functioning properly. You can also drill 2, 1/8" holes in it to help with flow.

 

NO!

Removing altogether will do more harm than good as the flow will be too fast and the cooling effect will suffer.

 

I have a 94 with a new LT1 with less then 5000 miles on it that does the exact same thing but I turn the AC off it gets above 230. I dont have a problem unless it gets in the high 80's and I am sitting in traffic for a prolonged time but the problem sounds verry similar to mine. I have also removed the radiator and given it a good bath with no help. I havent spent a lot of time on the problem since I am building my stroker now and plan on getting a new alm radiator when I drop the new motor in but am courios about what the cause could be. The slow fan is post is an interesting idea, I wounder if there is a possible problem from the factory with these fans?

 

sorry.. 338* was a typo.. I ment 238*. Cooling fan motors were replaced 3 years ago (less than 20k miles).I dont think its the thermostat because when driving the car with the A/C off it runs a steady 186* almost on the screws... and when driving with the A/C it runs a consistant 198-212*. its only when stopped for over 15min at a stand still..

here is the best part.. I looked in the factory service manual for diagnosing the problem.. it said something along the lines of:

if the problem is overheating with the A/c under prolonged idleing inform the customer to turn the A/C off when prolonged idleing conditions exist - not further diagnostics are nessesary...

gee.. thanks GM!

 

I agree the slow fan is an interesting idea.. but since the fans are realtivly new i dont think thats it... how can i chjeck the fan RPM?

 

Are the fans running at high speed? I don't remember if the fans have low and high speed settings (via the PCM). Is low speed one fan or both fans turning at a lower rpm.

I think if you had another Vette next to you to compare with while idling that you could tell by the sound, etc that the fans are turning at the correct rpm

 

The old "no thermostat will cause it to run hotter" is an old wives tale. It's not a great idea, since it delays warmup and hence causes increased wear and emissions, but the thought that the water can't cool off because its going through too fast is bunk.

 

It may be the guage. The 338 deg. wouldn't do any good.

 

 

Had same problem I put a new radiator cap on and that fix it. H ope this helps.