Cooling System pressure

trumpetted · Post by **trumpetted** » 02 Mar 2012, 22:24

I have a 2001 s80 2.9 with 176,00 mile on the clock. I was experiencing some coolant loss to I installed a new reservoir and cap. The system would not pressurize and coolant sprayed out of the top opening of the reservoir so I replaced the thermostat (original/9+ years old. I also changed out the radiator hoses.) Still had the same problem so I gave up and took the car to a local trusted mechanic. He capped of the top opening in the reservoir with a small rubber plug and reported the cooling system seemed to be fine. The system built up pressure and coolant seemed to be circulating. I opened the cap to bring the coolant level up to mark on the reservoir and now the system will not pressurize. The temp gauge is right in the middle where is has always been and the top radiator hose is warm. I also have heat in the car which I did not have before so the coolant does appear to be circulating. Is there some magic trick to getting the system to pressurize again? As I stated, there is heat in the car which I did not have before and the top radiator hose is warm which also was not happening before. But now no pressure. Thanks for any advice!

Post by **JDS60R** » 03 Mar 2012, 09:49

Sounds like a pressure cap issue. Pressure test the cap you have (free at advance auto) and let us know what pressure it holds.

When the car is warmed up the top hose should be hot and hard to squeeze closed. Because you ran the car low on coolant ( no heat indicates this as the system has no valve to close off coolant to the heater core) there is no telling what other damage occurred.

Start with a tested cap and then we can work from there. Because the system has many components ( all of which can fail ) you will have to go on a fact finding /testing mission to resolve the concern.

Post by **dcarlson12** » 03 Mar 2012, 12:50

How do you know the system is not pressurizing? I am a bit lost here...

Post by **regent** » 03 Mar 2012, 13:01

In a sealed system, pressure increases due to thermal expansion as coolant temperature rises. The expansion tank cap has a release valve that will prevent excessive pressure build up in the system.
Makes sense?

Post by **boosted5cyl** » 04 Mar 2012, 08:27

Unless the temp gauge is going past the halfway mark or you are still experiencing coolant loss I would not be concerned. The system pressurizes in relation to the heat of the coolant in it. Sometimes you can run the engine and if the coolant doesnt get all that hot there will be little to no pressure in the system. Totally normal, nothing to worry about...

If your heat is working, the temps are normal and you are not loosing coolant you are fine. Yes it is a pressurized system but it isnt always under pressure.