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Old 18th October 2020, 21:23
cbjroms cbjroms is offline
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Join Date: Jul 2011
Location: Hampshire
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Yesterday I unbolted/lifted the radiator so that its filler was above the thermostat housing. I fllled the radiator until the water was level with its neck - thus I knew that the thermostat housing and radiator were filled with water and that there was no air in that hose. The expansion bottle cap was in place and the level was correct as per the marking on the bottle.

Leaving the radiator cap off (as it was temporarily higher than the thermostat housing) I ran the engine until it got warm and then replaced the radiator cap and continued to run the engine until everything got nice and hot (temp gauge read normal). I then turned the engine off an allowed to cool, at which point I removed the radiator cap and found the radiator was not full to the top. So I loosened the expansion tank cap, water started to come out of the radiator filler and so I repaced the radiator cap. Went through this cycle a number of times (radiator was clearly getting very hot) before lowering the radiator down and bolting it back into position.

On road testing the car the temperature gauge remained unusually low but when I got back and stopped in the garage the expansion tank starting venting water, all hoses felt hard (there seemed to be bubbling/boiling in some of the hoses) but the radiator was cold to the touch. I also noticed that a couple of new water leaks had developed and thinking that the cooling system was over pressurising? After the engine had cooled, I removed the radiator cap and it looks as if there is no water in the radiator.

Could a stuck thermostat cause water to be pushed out of the radiator into the expansion bottle?
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