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Coolant line filling with air

1526 Views 9 Replies 6 Participants Last post by  number9
I replaced the thermostat in my 99 Disco II, and after replacing it one of the coolant hoses (coming from the bottom of the block back up to the thermostat) is expanding like a balloon. The longer the engine runs, the bigger it gets. Opening the top vent screw releases the air/gas, but it just gets more in there after I close it up again.

Looking for ideas on what could be the problem. It did not have this issue before I changed the thermostat, but it was overheating with the old thermostat (I changed it to try and fix that issue thinking it was stuck).

Any help is appreciated.


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Your system coolant level may be low. That hose goes to pump, if not enough fluid in block hot gases expand. Did you refill and bleed system after thermostat change?

Possibly bad from stock thermostat, reinstall old one to see.

Found easiest and least messy/wasteful way to top off/bleed is by removing bleed screw and slowly adding fluid to bleed fitting using a small funnel. I will do this cold, prior to first start of the day with reservoir and cap in place. If reservoir is a bit low top-off to full mark. After a thermostat or coolant change it's a good idea to repeat this process several time/days because it may take awhile to get the most air out of cooling system.

Always consider the source and make your own judgment
Source considered.

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