For the last few months my car, 92 RS tbi, has been running at a steady 240-260+ degrees after about 10 minutes of driving, highway or traffic. I replaced the radiator(leaked), water pump(spewed), hoses, clamps, radiator cap, added homemade side fan shrouds, fixed air dam, and flushed a few times. Every time I replaced something I was sure that was going to be the fix. There were no leaks, good circulation, the top hose was getting water through it when the thermo was supposed to open, and the fan worked. All of this added up to exactly no change in temperature. Yesterday I decided to do everything else I could think of. I changed the thermostat, got another new cap, made sure there was no air in the system, and turned my timing down from 8 to 4. Suddenly I'm running at a steady 160-170 with or without ac. I haven't even needed the fan with the ac off and it's 100 degrees out there. I don't know which one fixed it but I'm very excited with the results. Good luck to everyone still trying.

 

I only hope the sensor is still working correctly!

 

Betcha it was the t-stat...