What would cause coolant to rise and fall in the radiator?

[BillRod]

Hi All

What would cause coolant to rise and fall in the radiator?
As it warms up with the cap off I can see the coolant rise up to just about spilling out a little then the level drops about two inches, then rises to the top, then falls again. It constantly does this about ever 20 or 30 seconds.

Thanks
Bill

 

[Big Jim M]

There should be NO AIR in the radiator. With the cap on and the coolant full to the top the cap allows 15 pounds of pressure and keeps the radiator full. What you are seeing is prolly the thermostat opening to let coolant flow and then closeing when the cold coolant reaches the thermosat again.
With the cap in place if the coolant spews out the coolant tank it is a sign you have ruint a head gasket.
Big JIm

 

[IMenriched]

Hi All

What would cause coolant to rise and fall in the radiator?
As it warms up with the cap off I can see the coolant rise up to just about spilling out a little then the level drops about two inches, then rises to the top, then falls again. It constantly does this about ever 20 or 30 seconds.

Thanks
Bill

to some degree this happens naturally. most likely the T-stat is opening and closing...when you see the rise and fall.

do you see a bubbles gurgling up?? you shouldn't