1990 Acclaim heats up when idling

I have a 1990 Plymouth Acclaim with a 2.5 litre engine that heats up very
quickly (not to the point of overheating but close) when idling. When I say
quickly, I'm talking about a matter of seconds. Also, when driving along the
temperature guage sways back and forth. The rad and thermostat have been
changed, and all the air has been purged from the system yet the problem
persists. The really strange thing about this is when the temperature
control is in the cool position, the problem is less prevelent. The coolant
appears to be circulating fine in the rad and the fan manages to cut in
before any overheating can occur. The is no coolant in the crankcase, no
white smoke from the exhaust and overall the engine runs fine so I don't
believe this is a head gasket issue. The belts are all new and the tension
is fine as well. Could it be that the water pump is staring to fail? Any
help or input would be greatly appreciated.

Thanks

Rick

Boy, you got a tough one, I would say you probably got air bubbles in there or else that temp gauge is a little screwy, maybe there's some kind of sludge in the water pump impeller!

have you changed the oil reciently? And running the air conditioner actually heats your engine more sometimes, many people are unaware of this though.

Clean the contact on the temperture guage sending unit or replace the whole unit!! This will be the one in the engine block not the thermostat housing. And see if that cures it!! :smoker2: