Recently bought a 2002 2.5 V6 S-type 85k very cheap as previous owner said they had been told headgasket going or gone. No smoke from exhaust, no sludge under oil cap or dipstick and no loss of power, but did warm up quickly. As the price was extremely cheap and I have space and some spare time I went along knowing that i'll never loose my money if I had to strip the car for parts.
Once the car arrived home on the trailer I used a sniff tester to check for exhaust gases in the coolant. Low and behold, the colour didn't change! Removed thermostat and tested in pan of water, and this did seem sticky. Ordered a new thermostat along with header tank & cap and 2 hoses that had seen better days. swapped all over filled up and bleed. run on the drive for 50mins upto temp ticking over lovely with very hot air from interior blower and coolant level sat level the whole time.
Took to work next day and checked level on my lunch. It needed topping up! Topped up same 13mile journey home. checked later that evening and level was still at max!
Ran it again on the driveway for around 10/15mins and when i check the next day the level had dropped again.
This weekend we pressure tested the coolant system and checked coolant for exhaust gases again and all good. Removed new thermostat incase that was actually a dud, but car got hot again on test drive.
Running out of options. Thinking either Waterpump, Radiator or heater valve. Can anyone think of or know of any other common issues it may be?