make sure the electric fan on the radiator works. It should cycle on and off as engine temperature rises and falls. It should DEFINATELY be running when the car is "overheated". If it's not, then that's the problem.
I am getting intermittent overheating on this car. It's a 5-speed,
>92,000 miles, water pump replaced at 80,000. Now has a new thermostat
>and radiator cap. Hoses seem to be fine.
>
>The temperature gauge readout is normally just below the midpoint. It
>will creep up to the midpoint, and I experience boilover at the
>overflow tank. I have not been running the air conditioning; ambient
>temperature has been about 85 deg. F., and it is more noticeable at
>idle. When it's overheating, if I go from a stop to driving speed,
>the temperature gauge readout drops as well.
>
>This occurs during a 6-mile commute, driving at 55 mph, with about 6 >stops.
>
>I've replaced several things on the car; the problem goes away, and
>then it's back. Any suggestions?