bad thermostat, or normal?

[DirtyJim]

Been working on the 72. Ive got the 360 with auto trans. I rebuilt the carb and other sorts of goodness and the engine runs like a champ. After running the truck long enough for it to warm up I noticed that the water in the radiator was under a lot of pressure (as evidenced by spewing when the radiator cap lever was released) but the water in the radiator was cold. Water in the engine is hot because all of the hoses are hot except the radiator hoses. Is the thermostat stuck shut? This is my initial thought, but I wanted to run it by the experts first.

[fordman]

soudns like it. or it didnt open up yet. but if it was spewing it should have been hot. they will spew when really hot. as if it had a cracked head or bad head gasket. i've never seen cold water spew out of a radiator.

[cdeal28078]

When you were working on those other goodness projects did you change out anything to do with the cooling system? Any like a radiator hoses, heater hoses or the such? If you cracked open the system you could have some air pockets in it.
If so park it up hill, take off the radiator cap and crank it up. Let it warm up and run for a while keeping check on the temperature.
clint

[Dragon]

The Thermostat definitely did not open A lot of thermostats even for our trucks will have a small air bleed that is why the pressure built up in the radiator.

[fordman]

yeah when i clicked submit i reliezed it could have been air locked. try bleeding the air out first . refill with water and let it run for a little . then see if it does it again.

[DirtyJim]

Alright....I just wanted to make sure there wasnt something drastically bad happening. I didn't run the engine long enough for it to get real hot. To be safe, I took the thermostat out and will leave it out until I get a new one. I have water flowing through the radiator now! Brought the old thermostat in the house and dropped it in a pot of rapidly boiling water and it opened about 3/16" after a minute in the water. I think its toast.

[Dragon]

Nope that is about right. For size and only thing you don't know is what temperature it opened in the house at.

[habu]

easy way to check it is put it in a pot of boiling water and see if it opens, if not it's shot

[fastEdsel]

A mechanic once told me that if a thermostat fails in a big block, never take the thermostat out and run the engine without one. Because the water pumps are so good in these engines, what happens is that the front two cylinders on each bank get cooling but the rear banks do not get the circulation and they can get severely overheated. So even if you are on your way down to the parts store in your truck to buy a replacement thermostat, put some kind of a restrictor in the housing even if you have to knock out the center of the thermostat but to make sure there is some kind of resistance on the coolant and all the cylinders get the same amount of equal coolant temperature. A metal plate with a hole in the center about the size of a quarter is a decent temporary fix.

[Dragon]

Not really true. We ran racers for many years without thermostats until we figured out the motors were running too cold. We never cooked the rear cylinders. That is when restrictors appeared on the scene. The ports on the water pump flow way more water then the front two slots in the block that feed each side head. So the rest of the water goes up into the back of the heads and have to come all the way to the front. Most FE head gaskets sets have a small water hole at the front and a large water slot at the back to force the water to flow through the block up to the heads and come back to the front to get into the intake water jacket.

[fastEdsel]

I suppose that running the engine at a very high RPM might be different alright. The mechanic I visited with however did not say what the condition or age of the engines in question was. I'm sure he was referring to daily drivers. I am familiar with the FE head gaskets and their porting, a design by the Ford engineers after learning hard lessons about their over heating problems with the flat head V8's.

[Dragon]

Even Daily Drivers.

[DirtyJim]

No worries...its all back together with a new thermostat in place. Works like a champ now. Thanks everyone!