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Coolant line filling with air

1525 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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If the hose has expanded that much it needs to be replaced for sure!
Regardless of the bleeding, that is a lot of pressure. To much pressure!
Why originally were you changing the thermostat?
I assume you put in a 180deg thermostat?
Having that much pressure could be a bad cooling system cap. Or possibly an indication of an internal issue such as a head gasket leak (I am dealing with similar on my 2002 D2)
As for bleeding, you need to bleed it from cold.
Pop the resivor out of its mounting clip and raise it as high as you can hold it without pulling on the hoses, fill with the bleeder cap loosened until you get a steady stream of coolant and no more air. Once you are comfortable you have all the air out close the bleeder and then re mount the Resivor.
Start and run the engine at idle with the resivor cap off, heater on full hot heat you should see a solid stream from the small hole inside the top of the resivior.
Monitor actual temperature DO NOT rely on the dash gauge. They register the same 150 to dam near 240 which is way too hot.
Temp should be under 190deg with a 180 deg stat and under 205deg with a stock stat.
Let us know what you see tomorrow.
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:devilEveryone please remember that Internet advice is not always accurate! Always consider the source and make your own judgment
Here is a perfect example of bad advice:devil!
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.

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