I've been having overheating problems for a while when stopped and finally while driving in the Mountains of New Mexico it rose pretty high climbing a mountain at 70 MPH.

That's it I new it had to come out for some Attention!
I was going to take it out but went ahead and took it to a shop for a replacement after all it likely is 14 years old . 95

The owner said when he called me that it was stopped up inside and outside.
He said the radiator was fine so I had him clean it but went ahead and replaced it anyway.
Also and get this cause pressure has to be maintained on these cars to ensure the cooling system works right.
He showed me my cap on the expansion tank I had a bad seal [ Hard and split ] and this is the biggie everyone should check if you work under the hood or someone else does work.

The return small tube going back to the expansion tank was cracked
[ loose ] allowing pressure to escape and causing the system to not be efficient.
IF YOU CAN WIGGLE IT IS NOT GOOD !

Ordered a replacement tank and a cap from a supporter of this forum for $ 109.00 including shipping.

Every one of these cars is at least 13 years old and this plastic stuff gets brittle with heat and age.

Any one needful of a good cleaned C4 91 to 96 Radiator in the DFW area PM me and I'll be in Hurst next Wed. night at the Rosa's get together .
I'll donate it if you feed me and I'm on a diet so I don't eat much !

Good company , lots of Corvette Eye Candy and almost free raditor !
And as a bonus you get your cars picture on the NET !

You'll never get a better deal than that !

 

I dumped my factory radiator for the same reason, plastic tanks

You can get AL expansion tanks now.

 

I may be wrong, but I don't think there is supposed to be pressure at the expansion tank.

 

There's no cap on the radiator.

The expansion tank is pressurized.
The cap acts as a pressure relief valve.

The overflow tank isn't pressurized.

 

Watch out for the road debris that can build up also and cause problems.

 

My '85 has a radiator cap as well as the overflow tank and cap. It has no pressure at the overflow. The newer models must be different in this way as well.

I replaced the valve cover gaskets and after the first test ride, I noticed coolant on the driveway. I think it may be low on coolant now because I went 80 miles or so with it staying between 185-190 (normal) and as soon as I stopped for the first light in town, it jumped to 200+ and the fan kicked in.

Could I have possibly done anything to make it lose coolant when changing the gaskets or do ya think it was just a coincidence? If I did something to any of it, I cant tell ya, the two dont seem related and I dont remember messing with any hoses or anything coolant related.

Hopefully it wont be raining this week and I will check the engine compartment for leaks. I guess its gonna sit in the drive until I figure it out.

 

Just did the same thing -valve cover- and had the same result; coolant leak. There is a short heater hose from the water pump to the heater lines. It runs under the A/C bracket. I had to take eveything loose and replace the heater hose. Took about 4-5 hours. Even if the leak is not in the hose you will have to loosen all this up just to see.
And, yes, our early model C4's do have a different cooling system layout. It's more traditional.

 

Yeah 91 -96 are the same and the radiator fit's those years !
For those who do not think holding pressure is important there's this.
Water boils at 180 degrees at sea level .
Every pound of pressure raises the temperature it takes to boil the coolant in your radiator.
With today's cars you must maintain the pressure characteristics to at least 15 pounds for good cooling.
A couple of other cooling things.
The later models computers are looking at engine and exhaust temps. to determine fuel / air ratio's so don't put too cold a thermostat in unless you reprogram it. A 185 is good enough.
Always run a thermostat because it actually helps cool your engine by keeping the coolant in the radiator longer thus cooling it more before it cycles back through the engine.
Some aftermarket computers like my Accel Gen. 7 computer on my hot rod 95 accually call for a 160 degree thermostat but not any stock computer I've seen.
You have to pull the radiator on any C4 with A/C coil and clean the debris from the front the time determined by amount of driving and the amount of loose grass and leaves on the roads.
Inside flushing is recommended for every three years with a change of coolant and you should get by without getting it rotted out on the inside for quite a few years.
If it's neglected it will need to be pulled and cleaned professionally.
This time of the year is a good time to get it ready for summer with the full treatment cause I got a really good deal on the parts and labor .
It's the slow time of the year.
You can buy a $600 dollar Alum radiator but if properly maintained the stock set up cools even my 450 HP LT 4 hot rods engine idling in traffic just fine. KEYWORD PROPERLY MAINTAINED !