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79 Midget 1500 overheating

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George P

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My 79 Midget 1500 is overheating to the point where the temp went above 100c
I had a 85c stat fitted so I removed it and ran the car without a stat fitted. Temp dropped to around 60c
I then fitted a 76c stat and went for a run today. After about 1/2 mile the temperature rocketed to above 100c but the engine did not seem to be boiling. After a further mile the temp then dropped to about 80-90c At that point I got home and garaged the car.

Before all of this I bled the whole system, I'm sure there must be air locks in there somewhere but I'm dammed if I can clear them.
I disconnected the header tank and raised the pipe higher than the engine fill point then I added water. The heater is disconnected and bypassed, whether that has something to do with the problem I'm not sure.

There doesn't seem to be any leaks around the head!!

If I remove the expansion tank cap several hours after the engine has gone cold I can feel that the system is still under pressure.
All hoses have been changed for new ones and a new stat is fitted 76c and a new expansion tank cap.
Some time back I fitted a pressure tester to the expansion tank and raised the pressure to 15psi. It held steady.
This issue has plagued me for a long time now. I'm worried I may have done some damage so how can I check the block ?
Clearly I'm missing something.
Help me, where do I start.

Thanks
 
George, these little critters can be very annoying - especially around heating/cooling. I have never used the expansion tank for the operations you are describing - instead I use the big brass nut with the slot on the top of the rad. This is higher than the tank and this is where I burp it. Full disclosue I had my rad rebuilt and my engine block boiled when I was restoring the car but have not had heating issues. The different times I have had the rad out and refilled it, I have filled the rad through the brass nut hole and then burped the system by squeezing the hoses with the engine running. As a sidebar more than once with my car I have come out of a building or store (ie to a car with a hot engine) to find that it had burped rad fluid on the ground - I'm still not completely sure where that came from.

good luck and sounds like we are getting there!
 
JPSmit said:
George, these little critters can be very annoying - especially around heating/cooling. I have never used the expansion tank for the operations you are describing - instead I use the big brass nut with the slot on the top of the rad. This is higher than the tank and this is where I burp it. Full disclosue I had my rad rebuilt and my engine block boiled when I was restoring the car but have not had heating issues. The different times I have had the rad out and refilled it, I have filled the rad through the brass nut hole and then burped the system by squeezing the hoses with the engine running. As a sidebar more than once with my car I have come out of a building or store (ie to a car with a hot engine) to find that it had burped rad fluid on the ground - I'm still not completely sure where that came from.

good luck and sounds like we are getting there!
Click to expand...
Thanks JP, well this morning I bit the bullet. Rad out, water pump off and a new one ordered. I noticed again water on the garage floor at the front of the car. I'm pretty sure now the pump has been leaking for some time. I have tried 2 thermostats, filled the system countless times and still get heating issues, The frequency of adding water should have told me it was leaking from somewhere so I decided to replace the pump. I'll let you know how it goes.
 
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