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Took midget for a spin yesterday.

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I am not which system is on a 75. The Moss catalog was not clear on the years. On a 79 the expansion tank functions as a remote header tank. You need to use a thermostat that seals at both the top and bottom of the radiator neck and has the valve to admit the coolant back under vacuum conditions. Sometimes when the radiator is mounted low in the car they mount the expansion tank higher in order to purge the air out of the system. The 79 has the radiator connected to the expansion tank through a 1" diameter hose and the expansion tank connected to the over flow tank with a 3/8" hose. The radiator has a fill plug and the expansion tank has the radiator cap. Thus when the engine cools off the coolant is pulled back from the overflow tank into the expansion tank eliminating the air from the system reducing corrosion and increasing the boiling point. I added a Midget expansion tank to my TR3 as an overflow tank. No more antifreeze drips on the garage floor and better cooling. Can't say it helped the oil drips though.
 
I think if you look at the 1275 or 1500 Midgets with sealed radiators (radiators that do not have their own cap), you'll find the sealed radiator draws fluid from the expansion tank which has a pressurized cap.....on NA cars, the expansion tank dumped through a hose directly onto the ground in the event so much fluid was displaced from the radiator that it overfilled the expansion tank....there was no overflow tank on those cars, just an expansion tank.
 
Kim, have you tried just running her without a thermostat just to see what happens? The unrestricted flow should keep her running "too cool" (Just as a check!)!
 
bugimike said:
Kim, have you tried just running her without a thermostat just to see what happens? The unrestricted flow should keep her running "too cool" (Just as a check!)!
Click to expand...
I might try that just to see if it helps anything. The cooling fan will still cut off and on and give a bit of heat regulation.
 
Kim, I really think this could be your head gasket again.

I have had these exact symptoms on several cars. The problem was always a head gasket seal that was failing, but had not completely failed yet. Under load, or after driving for a while, exhaust gas would escape into the water and get things hot.

However, you could cruise around for a very long time without cooling issues. But once it started getting hot, it was all over.

I generally solved this problem by driving the car and scratching my head until the head gasket failed completely. Once the head gasket was replaced, the mysterious overheating issues magically disappeared.
 
If it were the head gasket, wouldn't it miss when you first start it - until it burned the anti-freeze off the top of that piston?
 
I don't think it is the head gasket. I have another new one but I have had several different head gasket issues on cars and this just does not seem like one. I do have some dye I can put in the water and check for exhaust gases though. I might try that this week end or something. Come to think of it though, this might explain the pressure in the system after it has cooled off. Maybe some exhaust gas is leaking in and pushing out the water. Hmmn. I know I retorqued that head too, but maybe I got a head problem in there. This car did the same thing 10 years ago when I had it on the road. I was hoping all new clean stuff would solve the problem. No fogging up or smoke out the back of any kind though.
 
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