Thank you Ethan Rode for the YouTube video link. After sitting through the whole thing I suspect that I have a blown head gasket (argh).

Sorry, I forgot to mention that the fan was operating fine.

Could it be a clogged radiator? The radiator is new, so I don't suspect it. But it wasn't a Volvo OEM part.

My 960 Wagon started overheating. I have recently replaced the leaking top radiator hose, which led to a crack in the top radiator hose fitting, which led to a new radiator being installed. A few weeks later the temperature gauge slowly climbed toward the red one night, so I checked coolant level ...

Thanks! The 1/2" socket drive extension worked the trick (along with having it in the correct orientation to get past the clip).

I know its a simple question. But do I just pull it out? I've got a Vicegrip on the square yellow top and can push the spring clip to the side. It spins freely put I simply cannot pull it up. There can't be threads?!?