I have a '96 that was not driven for about two months and now the Low Coolant Light comes on after it was operated at normal temperature and cooled and driven again. I made certain all the fluid levels were OK before starting it and the coolant tank was full and the recovery tank was about 1/2 full. The cooling system has a 16# pressure cap that was new about three months ago and has been tested recently.

What I have observed is the engine never shows to be above normal temperature but when I check the coolant tank, the fluid is very low (but not empty) and the recovery tank is almost 3/4 full. What I expected was for the coolant tank to be full again once the system has come back to ambient temperature but it isn't. If I refill the coolant tank and follow the "burp" procedure to ensure the free from air, the system will be low every time after operating at normal temperature and then completely cooling. If I don't refill the system, the car doesn't overheat or run above normal temperature - the Low Coolant light just comes on at times. I even removed the line from the coolant tank to the recovery tank to ensure it was not blocked in some way but it was OK.

I am considering putting a 17# or 18# pressure cap to see that might help contain the cooling fluid but I am afraid that much pressure might damage the heater core (or other items) so I am looking for some help with this problem.

 

Check under the water pump to see if it is wet or dripping. Could be loosing it there.

Check all the hoses also.

 

The easy thing is to replace the radiator cap, and perform a coolant pressure test. I always do this anytime I replace a hose. Also, the colder weather could cause coolant leaks to happen. I guess the coolant hoses can shrink in cold weather.

 

I have not been able to locate any coolant leaks anywhere including behind/under the water pump and there isn't any indication of water in the oil. The system always has pressure on it when I have checked the fluid level. I guess my next step will be to install a higher pressure cap. Does anyone see any problem with the 18# cap?

 

Put a pressure gauge on the system and see if it holds pressure. That will tell you if you have a leak.

 

There could be a very tiny leak in the Head gasket causing the coolant too be sucked into the combustion chamber and being burned with the air fuel mixture.

There won't be any external coolant leaks on a head gasket failure.

 

Are you saying it is pushed into the recovery tank and doesn't return to the engine on cool-down? That could be as simple as needing a new pressure cap. The cap has a little valve in the center to let coolant pull back into the radiator as the pressure drops (as it cools). If that isn't working, it won't pull coolant back in.

If that's the problem, the coolant should only ever be but so low, and as the system heats up it should expand back to "full".

It could also be combustion pressures pushing coolant into the overflow. This would not be good. When it is running, you could check for bubbles through the overflow tank (the white non-pressurized one).

I would not install a higher pressure cap. What potential issue would that solve?

 

Fill out your profile or mention where you are located. Some other member near you may have a pressure tester for your cooling system. A pressure test should be your first step. If you are in central Illinois I would be glad to test it for you.

 

Just had this happen on my stock 91 TPI. Coolant was being lost and got more and more progressive. Performance was good with just a little stutter sometimes when going to WOT. This had been going on for a couple thousand miles and then the coolant loss begin to get worse. Originally thought could be the intake leaking, but after resealing the intake and pressurizing the system found coolant was leaking into the #7 cylinder. Culprit ended up being the head gasket. If you do need new head gaskets, get the good quality ones from GM, not the cheap ones from the auto chain stores. The extra money will be worth it in the long run.

 

Check the hose that goes to the recovery tank. a cracked hose will make the coolant build up in the tank without being pulled back into the engine on cool down.
If the water does not go back into the engine, there could be another hose in the system that holds pressure, but won't hold vacuum.

 

The gasket on the top inside of the pressure cap has to seal with top lip of the coolant tank. If not a good contact or seal, it could let air in and not pull the coolant from the recovery tank. Make sure it is a proper corvette pressure cap.

 

In your owners manual it specifies for a coolant change a supplement is added with the new anti-freeze. Do you know if this has been done on each coolant change? The supplement is to prevent leaks.