OK, I've been chasing a low coolant issue for some time. I get into my 89 and within 1 minute of driving I get the low coolant, then once the temp reaches about 165 it will go out? Now I know that when the thermostat opens the entire system will be circulating, but if the level was low in the beginning, how would it get better once the stat opens? I know the low coolant sensor is midway down on the radiator, just seems odd that it "corrects" the level to some degree? Last time I added fluid I did the burp technique also.

Could it be pulling the extra fluid in from the overflow?

I don't see any pooling water after parking either?

I'm starting to think the only way to figure this out is a pressure test to see if there is a real small pin hole leak someplace?

 

If the radiator is losing any coolant at all, I would suspect a Head Gasket leak. Especially, if you don't see any external leaks.

The coolant gets sucked into the combustion chamber and exits with the exhaust. If it's a minor head gasket leak, you wouldn't see any white smoke from the exhaust.

 

Once again I think the pressure test is a must due in order to see if there is a small leak in any of the hoses/fittings, several of the hoses are original (1989). Not sure if this would tell me anything about a head gasket issues though?

 

I sincerely hope you don't have the same problem I just had fixed in my 89. The symptoms were exactly the same as yours. At the beginning, the Low Coolant light would come on and I would have to top up the system once every two months, then once a month, then... Turned out to be a head gasket leak about mid-way down the drivers side. I ran a pressure test for 1 1/2 days and got just the tiniest bit of coolant on the floor. After taking it to a shop, they found it after getting the car warm and putting it on a lift. All you could see was the small trail of coolant down the side of the block, no liquid on the ground or white smoke out the tailpipe. Also, the blue liquid test for combustion gases in the coolant was negative. According to the shop, both head gaskets were definitely bad.

What I think happened was that the leak was opening up when hot, which is why the system would never pull a vacuum as it cooled down and draw the coolant back up from the overflow tank. After starting it the next time, the coolant would be low until it expanded due to the normal heating, which is why the Low Coolant light would then go out. The trouble was that the leak was always letting coolant leave the system, so eventually, the coolant would get low.

 

With GKK