My 93 SI has 204,000 miles and runs well. At highway speeds (70-80mph) the temperature gauge will rise on an uphill grade. If I back off on the down hill side the temperature will return to normal. On a hot summer day, I is necessary to trun on the heat to avoid going into the red. I have replaced the radiator and am on my second thermostat.

Any Ideas on a fix???

JPrest