What is the correct way to purge air out of the cooling system of a 2001 s-type?
Has this happened?
Bought the car and ran fine. One day all of a sudden it gave the overheating light. I gunned it and the temp dropped light went out. The car ran fine for months with this happening every once in awhile.
Finally 5 months ownership it has decided to heat up on me all of the time.

Not a fan of how the system works but duable. So I changed the thermostat, again not fond of the o rings to stop leaks. The thermostat housing bolts wouldnt unscrew so yes I had to make them unscrew. I ended up making them longer with lockwashers and nuts on the back.
The system isnt leaking but I noticed that the resevoir will boil a little and the rest of the system seems ok. Im assuming it hasnt been purged right because its back to every once in awhile overheating. By the way what the heck is the housings made of? Its like theres a plastic outside and where the hose attaches is a brittle composite of some sort.
When the guage does show overheat I do lose heat until I get on it... Something also seems to be sticking closed or then again air in the system might cause this. Insights from those that have been around the block with this engine is appreciatted. chad