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1975 Corvette Overheating


Aaron Stokes

Hi My names Aaron and this is the first time I have used the forum.

I have owned my 1975 Corvette for 91/2 Years but this year it has been overheating badly.

I have replaced the thermostat with a 160 degree one I have had the radiator rebuilt with a new core I have tried different coolant strengths, I have also checked the water pump and it seems ok.

The fan belt and radiator cap seem ok and I have flushed the engine through but the engine is still heading for the red after about 25 minutes.

I wont let this beat me but I am starting to run out of ideas.

Living in England doesnt help matters as parts from the US take about six weeks to arrive and buying parts in the UK are normally 2-3 times the price.

Any ideas would be greatly appreciated


1975 Red corvette

First of all, does it over heat all the time, only at speed, only with the air on etc. etc.

If it only runs hot, or starts getting hot while you are driving, check underneath and make sure the little lower front spoiler is there and in tact.

Check all the seals between the radiator and supports.

Check the fan clutch. When the engine is cold, the fan should spin free from the pump (engine off after the engine has cooled all the way down). WITH THE ENGINE OFF grap the fan blade and get a feel for it.

Then, start the car and let it get up to temp. After it is good and hot, shut the motor off and grab the fan blade. It should not spin easy. If it does, the fan clutch has gone bad.

Check your initial timing on the distributor. Make sure the engine is not running in retarded timing.

Check between the radiator and a/c condenser for leaves and debris.

That is about it outside of the things you have already done. If this does not do it, you may have a blown head gasket.

Check these things out and post back. We will await your response.
You say the engine is overheating but you did not list any coolant temperatures.

What is the range of temps you see?
The temperature is very slow to rise.

Before I had the radiator rebuilt the car was overheating in about 10 minutes. It has improved since the rad was rebuilt but not to how it used to be.

I am planning to take chris`s advice tomorrow and check the fan clutch.

The air conditioning is disconnected and the small lower spoiler has been missing since I bought the car in 1992. I will also check all the seals around the radiator. I checked the timimg and it is set a 6 degrees BDC as per the manual.

I have changed the oil and filter and there did not seem to be any water present in the oil. I think I will remove the plugs and do a compression check to see if the head gasket may have gone.

My biggest problem is time I have the rest of August and some of September left before the weather starts to turn and the car is taken off the road again for the winter.



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