My 1990 240 overheated yesterday, the needle just climbing to the bottom of the red zone on the temp gauge in stop and go traffic. On the highway at 60 mph the temp would drop down almost to normal. When I got home I looked under the hood and saw indications of boiling coolant in the overflow reservoir. The car ran just fine. Coolant level is at the minimum mark on the tank.
It's been running just a bit warm when the air temps is above 80F. My guess is plugged up radiator. Goes into the shop Monday AM.