My 95 keeps getting overheated when idling but cools down quickly when open driving. The overflow tank is full to the top but the black tank towards the dash of the car keeps going down. The fans don't kick on but have a cut green wire to the main relay. AC has new unit but only blows hot air. The back 2 spark plugs towards the dash of car aren't registering like the other plugs they read lower than the rest. The previous owner replaced AC unit and water pump. It doesn't blow any smoke and there are no leaks under the car. I posted another thread about this issue but don't think I put enough info about it so starting g a new thread. Is this a head gasket possibly putting combustion gases in the coolant? Did they put a wrong water pump in the car?I'm at a loss. I am not that mechanicallyinclined and know nothing about corvettes. I will replace the cap on the black tank but can't believe that a cap could cause the issues. Also the previous owner had the coolant flushed and replaced. Maybe they screwed something up I don't know. Thank you.

Mike

 

Why aren't your cooling fans working? When idling they are needed to cool the car. Once moving the computer will turn the fans off because there is ample air movement to cool the car. If your A/C is blowing hot air that too can be contributed to the cooling fans not working. I'm sure if you fix your fans your temperatures will drop.

 

No idea on the fans, but the black (surge) tank going down and the overflow tank filling up sometimes means that the radiator cap on the surge tank is bad and should be replaced.

 

Dupe

 

^This^.

This is where you need to focus your attention.

 

Fans first, get a FSM and go through the procedure. Make sure the relay is working correctly.

Then replace the radiator cap.

 

Do the fans come on with the A/C? They should.

 

No they don't.

 

What do you mean by overheating? 226F is when the fans are supposed to come on (Unless they had the ECM reprogrammed). My buddy just bought his first vette, and was panicking seeing his gauge at 235. Of course traffic and a hot day didn't help...lol. Any how, I recently went through this with the '96 I just bought. But since you mention you're not very good at the mechanics yet, I won't explain exactly what to do. Instead, go to autozone or any parts store and buy a Haynes Repair Manual, or unless you have the cash, buy the actual GM Service Manuals for your specific year, along with a digital voltmeter. In book's it will tell you about grounding the ALCL terminal to see if your circuit is good. If not, while the terminal is grounded you'll need to check for voltage going into the relay. There's a lot more things involved troubleshooting your cooling system. I also agree with RUU, check your cap. Also the C4's designed to "suck" up air and cool down various components while driving, especially with the help of a healthy airdam. With that in mind. There's gaps around your radiator/condenser shroud. Inspect and make sure no debris is caked over them. If so, clean it or them. C4 are the vacuums of the road lol

Why do you think your gasses are getting into your coolant?

Does the A/C have enough or any freon? Was the A/C orifice tube changed with it?

 

Doesn't the '95 have a PWM controlled fan? If so, it should start running at a speed lower than 226.

 

It has 3 relays for the fan. They all lit up with the light pen. But the cut green wore is dead. It gets up to 325 to 340 and don't kick on. I bought a new radiator cap that was 15 psi but it's just a generic on from Napa. Hope that's OK for it.

 

The only greens in the cooling system I can see on the schematic, is Dark Green: Coolant fan switch & Dark Green White: Cooling fan relay. Connect the broken green and see if it fixes your problem. If not, bypass the relay and see if your fan(s) turn on. The only thing left is the Coolant Temp Switch

As for the cap, it should work fine.

 

I put the new cap on I feel it definitely needed to be replaced. The old one came off easy without pushing it down to twist. The new one needs to be pushed down and then twisted off. Is it safe to test it out with the overflow being filled to the top apparently due to lack of pressure from the radiator cap. Or should I pull some fluid out of the overflow?

 

I'd drain some from the reservoir, that way hot coolant doesn't spill out onto the car when it heats up. Unless you don't mind it

 

Full. If it pushes coolant out, it will go to the overflow tank...not "spill out into the car".

 

Where does the overflow tank sit? On the inside of the bump right? As far as I'm concerned, that's still part of the car. Actually, it sits ON the bumper from the inside. Let's not get too literal, I'm sure the OP understands what I'm laying down. Beside, he's talking about draining the overflow tank because it's full already. And if you really want to get technical, it's called "Expansion Overflow Reservoir Tank"...

 

You may be right; If that tank is full, then yeah he could pull some out of it. I thought he was talking about the surge tank up by the fire wall being full...and misusing the terms for the two tanks.
What's odd is that if the over flow tank is actually full from expansion past a bad cap, why didn't the system suck the coolant back in when the car cooled? You shouldn't be seeing a net gain in coolant in the over flow tank from a bad cap....

 

If the seal is bad. It will suck air into the system from the cap when cooling rather than from the expansion tank. And vise versa when the liquid starts steaming. Without that steady pressure, your cooling system will not work properly. No matter where the leak may be. Here's a cool science project. Get a plastic bottle, Cut it in half and make a small hole on the lid. Fill the bucket with water and submerge the bottle, top facing up. Now place your finger over the hole and pull the bottle up. Once you get towards the bottom of the bottle, you'll start to feel pressure or resistance. Relax your arm and let the bottle return to it's natural state. Now do it again, but without your finger over the hole. The pressure within the cooling system basically works the same way. Without that steady pressure lock. You will always have cooling issues

My '85 had a lot of cooling issues when I first bought it 28 years ago. But with time you'll pick up on what to do. Don't be afraid to dabble with it either (but within your comfort zone). And slowly your skills will increase. Of course now you have the internet with hundreds of good guys willing to help, plus tons of information, unlike in '94. All we had were books, and our local tech lol.

 

Get the fans working. ASAP if you haven't already ! ! !

 

Ok. The coolant is retaining pressure with the new radiator cap. And I discovered by reluctantly letting it idle for awhile that the fan will kick on when it reaches 227 degrees. I just never let it get that hot. Only found a leak in the upper radiator hose and replaced that.