I just bought my first Corvette a few weeks ago and have a little problem. First about the car...It's a 77 Corvette, when I bought it, it had been sitting in a barn for about 5 years. Just before it was parked, the previous owner installed a new ZZ4, and had the trans and rear end rebuilt. I have the reciepts and all of these parts only have about 1200 miles on them. When I got it, it was in pretty sad shape. I changed all the fluids, new tires, new exhaust, and a new Edelbrock 750 carb. The car runs and drives good, though most of the suspension and steering looks original. The white paint is original and that's about the only positive thing I can say about it.

Now the problem.....The car is overheating, but only intermittently. It usually only does it in the morning on the way to work(15 miles of hwy). The temp gauge will rise to about 260 and stay there. When I go to drive it at lunch and on the way home it does fine. This morning it ran hot most of the way to work then dropped down and stayed at 180 like it normally runs. When it runs hot, the heat doesn't work. I replaced the thermostat and it was ok for a couple of days but it's doing it again now. I can't find any leaks but when I check the radiator, it is low but the overflow tank is full. I thought I had an air pocket in the system so I let it run with the cap off untill the thermostat opened up then refilled the radiator and that seemed to work for a few days but it's back to running hot. Could I have a bad thermostat? I heard once about drilling a small hole in the thermostat to prevent air from getting trapped, could this work?

 

May not be your problem but my 71 started to run hot. Did loose some fluid but could not see any dripping or leak. After a few times out and temp running hot I found the pass side rug wet. My problem is with the my heater core. Check pass side floor for any dampness.

 

Drilling the tstat is a good fix, 1/8" hole, it will allow the air to bleed thru where it should remain in the top of the rad. If it keeps happening there may be a compression leak. Are you losing fluid? Getting the air out of these things can be tough sometimes

 

Mine sat for 10 years before I bought it.
It would start out fine, then overheat.
Fluild would be disappearing. I couldn't find a leak.
Barrowed the cooling system pressure tester from Advance Auto.
The inlet on the radiator was leaking. It would blow out as steam while I was driving. When I shut the car off, the fuid would be lower than the leak and wouldn't drip.
The tester is free to barrow, and a good place to start.
I will admit I had to read the instructions for the tester. It has a zillion adapters to fit any car.

 

The coolant level is low.

 

You're right, every time I check it the coolant is low in the radiator but the overflow is full. After work today, I drove it to my shop (about 5 miles) and it was showing 260 on the gauge before I got there. The upper hose was very tight, I tried to remove the cap and it let off some steam then coolant tried to spew so I put the cap back on then the gauge dropped to normal. I removed the cap again and no spewing and the coolant level was about 4 inches too low. I shut it off and went to the parts store(15mins). I then removed the thermostat and there was no coolant in the hose or intake. I went ahead and drilled the thermostat and replaced the cap. It did fine on the way home but the real test will be in the morning as that's when it usually acts up.

 

could it just be the thermostat was sticking, drive it without the entire tstat in place and see what happens.

 

What about a bad Rad cap?? I had a car years a go with a similar problem, overflow filled and running hot. Cap would not open to draw from overflow. That coupled with an air pocket.

 

have you looked at the heat riser? was that replaced or removed when you did the exhaust?

it might be stuck closed, thus the reason you heat up once you start.

 

also, are you sure your coolant recovery tank is plumbed properly so that it can suck the coolant back to the rad when the car cools off?

 

Good advice above. Given the symptoms, if it was my car, I would remove the thermostat completely. Then, I would go through the coolant fill procedure and drive the car for a few days, either the problem disappears or it doesn't:

Problem disappears: test a new thermostat to make sure it is working, then put it in the car. Check the hose on the overflow tank to make sure it can take overflow and return it to the rad on cooldown. You should be done.

Problem persists or goes away for a few days and returns: Check coolant level again. If it is lower, you have a leak. If the coolant is still full, checking the heat riser (if you have one) and your chin spoiler (to make sure you have one) would be good things to do at that point. If the coolant level, heat riser, and chin spoiler check out, and the problem persists, it seems like it must be some kind of intermittent coolant flow problem (which is not the t-stat, since at this stage, I wouldn't have one in the car).

 

What about the water pump- could be going bad- not flowing enough fluid!!

Darrel1

 

Very doubtful. Water pumps usually have 1 failure mode: the bearing and bushing give out. For a pump to "Not flow enough" the impeller would have to corroded away or the fins to be broken. I have only seen 1 do that, several hundred bearings/bushings die

 

If it cools down at speed and runs hot in stop and go, check the fan clutch for proper function (I assume it has one).

Gary

 

Bad radiator cap, bad thermostat, or lower radiator hose collapsing at higher rpm's.

 

The symptom of getting hot and at the same time the heater doesn't work is typical of low coolant level. For some reason the coolant is getting out, either getting pushed out or leaking. You will have to determine where its going.

 

Just to update, I replaced the radiator cap and drilled two 1/8" holes in the thermostat and it seems to be fixed. Thanks for the help.