Thermostates

jacob smith

jacob smith

Senior Member
A have 2 barrel type thermostats for use in a 36 ford. I teasted them in water. One has a tight seal and opened up at about 175. The other does not seem to close tight and fully opened at about 165. Am I right to say that the thermostat that does not close tight and is not good.
 
jacob smith said:
A have 2 barrel type thermostats for use in a 36 ford. I teasted them in water. One has a tight seal and opened up at about 175. The other does not seem to close tight and fully opened at about 165. Am I right to say that the thermostat that does not close tight and is not good.
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A thermostat does not have to seal tight when closed. In fact they should have bled holes so some coolant flows through when closed. This is important at starting as a completely close stat will put a head of air between the stat and
engine and take a long time to open. When a small amount of coolant flows through at startup warm coolant opens the stat faster. Has nothing to do
with the operation of the stat after it is open. G.M.
 
G.M. said:
A thermostat does not have to seal tight when closed. In fact they should have bled holes so some coolant flows through when closed. This is important at starting as a completely close stat will put a head of air between the stat and
engine and take a long time to open. When a small amount of coolant flows through at startup warm coolant opens the stat faster. Has nothing to do
with the operation of the stat after it is open. G.M.
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Ok but if the thermostat has the bled holes in it should it close tight? And would the fact that thermostat is full open at around 165 and the other matching one is fully open at 175 mean that this one is bad. Or am I misunderstanding you
 
If you don't care how fast the engine warms up or whether it ever actually does you can use a faulty thermostat that doesn't close all the way. But, if you ever need the heater, like I did last night when it was 6°, you'll have a hard time getting enough heat out of the heater if the thermostat doesn't close all the way. Stock thermostats that have a bleeder hole have a stopper in that hole that stops all flow when water is pushed against it. Any flow through a thermostat when it is supposed to be totally closed reduces it's effectiveness.
 
My thermostats each have a small hole (1/16) drill size, and NO stopper in the hole.
You need a small bleed hole in the stat, so when you fill it with coolant, the trapped
air can bleed out of the engine, the coolant can fill the block and heads completely.












.
 
jacob smith said:
Ok but if the thermostat has the bled holes in it should it close tight? And would the fact that thermostat is full open at around 165 and the other matching one is fully open at 175 mean that this one is bad. Or am I misunderstanding you
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They don't have to close tight like a valve, .020 or .030 gap on one side isn't going to leak that much coolant. I would question trying to see EXACTLY when they open in a pan of water??? Put them on the engine, run them and check the temperature on the head outlets with a laser pointed thermometer. You can swop thermostats from side to side to see the true picture. G.M.
 
jacob smith said:
This gap is 1/16" you can fill in the spring that one has more tension on it then the other.
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If you have already made up your mind that one of them is defective then there is not much to discuss. Seems you have two ways to go, replace it or test it in the car as GM suggested and see how it preforms in an operating system. What other options do you have? Flatheads often run at different temperatures on each side, so you would most likely have to switch them to truly see how they are working.
 
JSeery said:
If you have already made up your mind that one of them is defective then there is not much to discuss. Seems you have two ways to go, replace it or test it in the car as GM suggested and see how it preforms in an operating system. What other options do you have? Flatheads often run at different temperatures on each side, so you would most likely have to switch them to truly see how they are working.
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It is not that I have made up my mind. I just do not want to loss my ability to return the one defective thermostat. For some reason the cost of a NOS after market thermostat is expensive. I am calling the parts house that I got it from on Monday to ask the question if I can test it as GM says. If not I will send it back and find another one. No reason to spend money on something that is not right.
 
I didn't realize you had the option to return it! If that is the case that is what I would do.
 
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