Bought my car in January and we have been steadily resolving issues. I have 1979 that p.o. said he had newly rebuilt the engine. We changed the oil right off and new distributor and spark plugs and wires, it had a one fouled plug. Changed the trans fluid, flushed the radiator.
1st problem with overheating I had drove to town about 20 miles, right before I got home the car overheated so we put a new thermostat in. It did not seem to completely seat at the gasket and was getting a very small drop of water every once in a while. We replaced the gasket with cork...no more leak.
Being that it overheated I'm paranoid and I watch the gauge constantly. It typically runs between 190 to 220 once it is warmed up.
If I'm sitting in traffic or if I'm driving over 2000rpm it will sometimes (Not always) start going up over 220 then it will come back down. Last night I was on my way home and I was driving around 55mph 2000 rpm for about 20 minutes and all of a sudden the temp gauge starts climbing. Before I could get where I could pull over it had pegged out! So I expect when I pull over to see the car spewing water everwhere and I get out and nothing...it scared the hell out of me!

 

what temperature thermostat did you install? with the engine cold is the radiator completely filled and the plastic tank filled to the cold line? Is your fan clutch working? With the engine off you should not be able to spin the fan by hand more than 1/2 turn.

 

Plastic tank has a hole in it and will not hold water

I will check on the thermostat, not sure it was whatever the parts store gave me...being that I've been given wrong thing before that is a good place to start.

I will check the fan next

 

Normal operating range.

Also normal.

Were you in stop and go traffic? Come off the interstate and stop at the top of the ramp?

Without the coolant recovery tank, you may be over filling the radiator. Fill it to within an inch of the bottom of the filler neck.

Order a replacement recovery tank.

 

Yes it was stop and go traffic...no interstate just Alabama highway. It would climb up over 250 and go back down when I started driving...then climb back up after I was going 55 steady for 15+ minutes. Just concerned me last night because it never went back down it stayed pegged out. Online looking right now for a new tank right now!

 

That's the root cause right there. The car will puke X amount of coolant every time it gets up to operating temp. You're running around with a low coolant level, no wonder the temp gauge is pegging out.

Cars with recovery tanks need to have rads that are 100% filled to the top all the time.

 

the parts store probably gave you a 195 degree thermostat. which was stock, engines ran around 200-210 for emissions purposes in 79. What did you set your timing at, that can have an affect on engine temps. and as mentioned before coolant overflow tank must be functional and clutch fan.

 

I am sure they did give me whatever it said in the computer to give me...so should I go back and get another thermostat? Ask for which one?

They were going to adjust the timing yesterday...its off... but missing the timing tab so I have to pick one up next trip to the parts store, sounds like that will be on my way home from work today! Vette is at home...I'm in the DD today!

Awww what we do for the joy of driving these old vettes

 

Keep in mind that a thermostats function is to control the minimum temp of the engine.

 

over flow tank can be fixed if it is a small hole .a screw with silicon on it will work till you can get a new one. please no bubba flames.

 

Ok went and purchased a repair kit...pulled the tank. I have found no holes, cracks, separating seams. The tank is solid...it was just stuck in the hold and was not attached but I put water and it has not leaked so the guy that told me that apparently did not know what he was talking about.
So...next step...timing
Timing tab is missing! ughhh

 

OK, I'm confused. If you THOUGHT it was leaking- you must have confirmed that it had no coolant in it. Right?

If so- the car is critically low on coolant. Fill it up to the cold or hot marks and monitor the level for a week or so.

 

I was told that it would not hold water...so I filled it with water last night, went back out there this morning, it still has water in it....no water on had leaked out anywhere. It's sitting on my garage table now. I'm going to fill it with water and do like you said, I have a feeling that the guy that told me that did not actually know.