Hello, my 1990 240 DL wagon's temperature gauge gets up near the red zone after idleing on a hot day for 20 minutes or so. I have flushed out the coolant, and after suspecting there was an air bubble in there, tried to "burp" it through the upper radiator hose, but it was completely full of coolant.
I should say, I am using regular green coolant and not the Volvo stuff, because I have a hard time believing there is a difference. Also, I have no idea if it is original, but the radiator is the Volvo plastic one. There are only a few things I can think of.
One being the radiator has accumulated gunk or rust along most of the fins, and is not cooling the coolant properly.
Two, the fan clutch needs to be replaced, but I just swapped mine out with a different used one, both of which seemed OK (did the "turn off the car- see if it turns after engine stops" test).
Three - its the temperature compensation board - although the times that it gets hot make sense because it's always after driving and then idling for a while in 95 degree weather - although the inside if the dash could be hot, too, and causing the temp. comp. board to malfunction. It goes up steadily and slowly, and then I usually shut off the vehicle, because I'm scared of it overheating. When I start the vehicle again a few minuted later, it has usually cooled off a little, but goes right back up close to where it was near the top red area.
If I go look under the hood while it says it's so hot, though, nothing feel hotter than normal to my hands. the expansion tank is not leaking, nor is anything else that I can see. The air blowing into the cabin gets a little warmer (I think), however. It hasn't happened when the AC is on, but possibly always when the dash is blowing air at me. The blower doesn't sound all that great, but, could it be causing this??