I'm having an issue on my 2000 S80 T6 where the upper radiator hose has too much pressure. It blew off once but there have been no signs of leaking coolant elsewhere. I changed the thermostat, radiator cooling fan, and the water pump and the issue is still happening. The car also begins to overheat and loses coolant and I'm not sure where it goes. I've ruled out that it might be a head gasket leak because the coolant is clean and there is no air coming out of the dipstick - not to mention the oil is also not contaminated. After I open the reservoir cap to de-pressurize the upper radiator hose, the coolant begins to rise and spill over. I have no idea what to do or how to remedy this so any help would be appreciated.

Also, the plastic guards below the car have been removed for a while and I don't see leaking.

 

It`s your head gasket. The coolant is drawn in as piston is on it`s downward firing stroke and then your cooling system is pressurized as it rises on the compression stroke. Your coolant is going out the tailpipe and will ruin your O2 sensors and Catalytic converters after a while. Depends on the location of the head gasket leak if coolant will contaminate the oil, so that`s not a for sure way to determine a head gasket failure.

 

Thank you for this. Does this also mean there won't be a large amount of white smoke coming out the tailpipe? I've noticed some on startup, but it becomes faint as the car warms up.

 

That`s another indication of head gasket failure, the worse it get`s the more white you`ll see. As the engine warms up the gap in the head gasket will close a little bit, so that`s why it goes away.