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radiator cap on automobile

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Carl:
The thermostat situation really can`t happen as described becuse the bulb of it is in the coolant in the block,and once warmed up will stay open unless the entire coolant in the motor cooled to a point that allowed it to close.
You would notice the guage rising to temp then falling and so on plus the heat in the vehicle would be affected.
Regardless it wouldn`t make the cap come loose.
They have to be pushed down and turned to lock into position as well to load the spring which allows the system to pressurize.
If it overcomes that pressure the rubber seat on the bottom of the cap is pushed against the spring and it will open the filler neck so that coolant will escape into the recovery tank or be lost through an over flow tube.

My guess is that the cap wasn`t tightend past the locking dogs and combined with the extreme cold the radiatior partly froze preventing the coolant from flowing down through the core.
This caused the entire cap to push upwards and also without proper circulation the coolant heated very rapidly behind the sending unit for the guage.
This is always located at the top of the coolant circut where the coolant is the hottest.

Make sure it is a 50/50 mix and the cap is seated tightly.

franksolich:

--- Quote from: Carl on January 25, 2008, 06:29:52 PM ---The thermostat situation really can`t happen as described becuse the bulb of it is in the coolant in the block,and once warmed up will stay open unless the entire coolant in the motor cooled to a point that allowed it to close.
You would notice the guage rising to temp then falling and so on plus the heat in the vehicle would be affected.
Regardless it wouldn`t make the cap come loose.
They have to be pushed down and turned to lock into position as well to load the spring which allows the system to pressurize.
If it overcomes that pressure the rubber seat on the bottom of the cap is pushed against the spring and it will open the filler neck so that coolant will escape into the recovery tank or be lost through an over flow tube.

My guess is that the cap wasn`t tightend past the locking dogs and combined with the extreme cold the radiatior partly froze preventing the coolant from flowing down through the core.
This caused the entire cap to push upwards and also without proper circulation the coolant heated very rapidly behind the sending unit for the guage.
This is always located at the top of the coolant circut where the coolant is the hottest.

Make sure it is a 50/50 mix and the cap is seated tightly.

--- End quote ---

Damn, you're good.

That's exactly what the mechanic told me today; the cap was probably only 99% on, not 100%, and all was okay for a couple of weeks, until suddenly temperatures plummeted to -22 F and below.

The cap is 100% on now.

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