hello, I have a 95 vette and am having overheating problems. I have replaced everything in the cooling system, thermostat, water pump, had radiator flow tested, and everything else we could think of but it still continues to overheat. Has also been pressure tested and does not have a blown head gasket. I work at an auto repair shop and we have spent all day for about 3 days looking at it and trying different things but still no luck. Are we missing something here? Someone please give me any ideas you might have as to why it could still be overheating. Thanks in advance for your help.

 

How high are your tempertures? Are your fans working when they suppost too work? The LT1 always runs hot, at around 225 even 230 and thats when your fan have to kit in. Mine was over heating behond 240, I changed the radiator cap and took out the radiator and clean the fins really good. The over heating went away. Do a search here on over heating and you will learn alot on the subject. Thats what I did.

 

I guess the first question is "How hot is it getting"?

Not trying to be rude, but most people getting into late model C4's for the first time are absolutely shocked by the normal operating temps these cars run at.

Normal:
Highway driving: 193 - 200
Sitting in stop and go traffic: 205 - 235

Your electric cooling fans won't come on until close to 228 F.
They will come on if the a/c system is running though. This is one car that will usually run cooling in stop and go traffic with the a/c on, than it will with it off.

Also, be sure and post the temp. that the digital display is listing.

So, I guess more details are needed on your symptoms before anyone can give further advice.

 

The LT-1 requires 3+ full cycles hot/cold to get the air out of the system. Until the air is out, the temp will fluctuate a lot and the analog gauge may approach 260F where the FSM says to shut it off and allow it to cool.
I've changed coolant with a complete flush three times in the 6 years I've had my '95. First and third times had no problems. The second time it took 5 or 6 hot/cold cycles before all the air got out and temps stabilized. And yes, used the bleed screw on the thermostat housing and the hot/cold cycle was from ambient to 260 and back to ambient (let it sit overnight). Took a week *&%^(%%.
Hope this helps.
PS Do not have the radiator pressure cap off at any time except when the system is fully cool and the engine is stopped. And use a 50/50 antifreeze mix, plain water will boil over. (Learnings from the second flush and coolant change.)
Also get under the front end or look from the passenger side between the A/C condenser and radiator. One plastic bag wreaks havoc.

 

i have the jet kit so the fans are staying on. it rides good for about 5 miles and then it starts to overheat. Almost seems as if the thermostat is not opening. The temp goes up to about 195-200 to start and it holds that temp for a while but then once it gets beyond that it just keeps rising. Just purchased about a month ago, was running perfect and then it just started to overheat one day and have had a problem since. Have done pressure test, radiator flush and no signs of a blown head gasket. Highest temp I allowed it to get to was 243 today.

 

Stuck thermostat, air in the cooling system or a cracked cylinder head. Test the coolant for signs of combustion by-products (there's a kit you can buy from NAPA for about $25).

 

Are you absolutely sure that when you replaced the WP, that you put on the WP coupler ? If you are overheating in only 5 minutes, I would venture to say that there is no coolant circulation. A stuck closed T-stat will also prohibit flow.

 

Did you bleed all the air out using the bleeder screw on the t/stat housing? It should be done first with engine just running, second time with engine running and t/stat open.

 

Is the water pump working (i.e. do you have/see water flowing under the cap in the pressure tank which comes from the hose on the top passenger side of the radiator)? If not could be the water pump drive coupling or driver gear.

Is the new thermostat the correct one for the LT1 (special design with extra plate on the bottom to cover the bypass chamber in the water pump) or has it failed (either mechanically -- the extra plate has a cap which fits over the main plunger -- ours actually came seperated after a boil over (left the cap loose) -- it can prevent the thermostat from openning all the way restricting water flow in and around.

Is the analog gauge's coolant temp substantially different than the digital dash temp? This could imply a flow restricting within the engine or spot boiling (insufficient pressure) or an air pocket preventing coolant flow through the engine. Frequently folks leave the cap off too long after starting the engine, preventing pressure build-up and movement of air pockets. Recommend cap off, start engine, confirm flow, top off, and then cap on -- all within 1-2 minutes at max.

Are both heater hoses hot and about the same temp? If not, perhaps there is a blockage which could cause flow restrictions and might contribute to the temps. Check the flow restrictor (looks like plastic connector in one of the heater hoses --- s/b near the wheel well.

Is there pressure build-up in the system -- i.e. when cap removed is there pressure? Has the cap been tested? Is there excessive increase in coolant in the overflow tank? If not, perhaps the cap is bad.

 

I found my water pump on my LT-1 had stripped the coupling between the drive coming out of the front of the motor and the water pump. It would work at idle but when RPM's came up it would get hot quick. I put an electric water pump on and now it is Puuurrrrfect.

 

I'm betting on the air bubble...system must be burped.