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If you've had old cars, you've probably at one time or another had one that would run hot. I haven't had a hot car in many years, but my 61 that I recently purchased, over heats on long drives over 70 MPH. I slow down to 65 or less and it cools down. I know, I know, "then don't drive fast". My question is, this car was purchased from Arizona and has no thermostat. As a kid I remember being told that if it over heats, to yank the thermo to help it run cooler. I also heard that it might run hotter because the thermo will restrict the flow some and hold the water in the radiator longer so it can cool? I've always known there has to be a correct answer and also a lot of opinions but usually, my problems were not thermostat related.
 

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if the thermostat is working correctly it won't cause a heating problem. most likely timing, or plugged radiator
I agree completely

If the timing is retarded, they work hard and run hot. I'd check that first. If nothing else, unhook the vacuum advance and set initial to 12, that'll be darn close, but best to check total, because if the mechanical is seized up, it'll do what you are seeing.

Radiators can look like they are flowing but tubes are clogged, that is probably it

Also

Check to make sure the fan isn't on backwards, although I doubt it if you drop back to 60 and it gets better, but its free to check, make sure airflow goes toward the motor, not toward the radiator

BTW - The "too fast through the radiator" is a misnomer which is based on truth. Stewart waterpumps has debunked it as a cavitation and pressure problem in the block.

If there isn't some resistance to flow (not pressure like a radiator cap pressure from heat expansion,but something to force the water into the nooks and crannies of the block), hot spots can turn to steam in odd areas. This can cause damage in diesels that use the water as support during combustion, but gas motors don't fire nearly as hard. In addition, without some resistance, the pump can cavitate, which also causes overheating and low pressure areas.

So yes, a thermostat can help, but not because it slows the water down in the radiator, its because it creates a little resistance for the water going through the pump and the block.

I'd bet my money on the radiator, but check the timing first.
 

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Check to make sure the fan isn't on backwards, although I doubt it if you drop back to 60 and it gets better, but its free to check, make sure airflow goes toward the motor, not toward the radiator.
Hey Mr. Stang,
Having the fan on backwards wouldn't make the air flow toward the radiator. You'd have to have the Engine running backward to get the air to do that no matter which way the fan is installed.

JC
 

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Rad shops use an infrared temp gun to see if there are cold and hot tubes in the rad - indicating restrictions. You can do that yourself.

+1 on cruise timing. Check that. You need both working mechanical advance, and working vacuum advance to get proper advance at cruise. Cruise timing is the primary purpose of vacuum advance, and without it, your heat goes up and your mileage goes down. Failed vac advance systems are also a primary cause of exhaust valve seat recession.

David
 

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My 390 runs hot with no thermostat but even at 45 mph but you did mention your car doesn't have one? What about clearance between fan and radiator, it should only be like 1 1/2 or so. Does it have a fan shroud? Another thing not mentioned is sometimes a good flush will help clean out sediment of rust and other junk in the radiator and block which reduces flow and amount of water. I have only driven mine a couple times for a short distance at 70 so no idea how it would act. But would think at 65 even, i would see the heat gauge creep up some before 70. A recore might do the trick but i'd try the flushing and if you don't have a thermostat try using one, along with checking fan clearance, timing etc before the expense of recoring.

Knock on wood i still have the original radiator in mine and it has done fine unless i'm in 100* temps and 15 mph in traffic.
 

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Yes, timing including vacuum timing, flushing/cleaning, shroud, hoses, all things I would try. Agree w stang and Deb, put a thermostat in there, make sure it seats correctly in the intake & housing without needing a gasket to hold it in. Replace water pump as a last resort.
 
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