I had issues with the heater core being plugged, so we cleaned it out with low pressure water hose treatment and that brought the heat back. I figured I would change out the thermostat at the same time and now I still have over heating issues. I have the fan on a toggle switch inside so that I can have it on all the time or as needed. Here is the issue. As long as the car is running and up in RPM, the temp stays good. If I stop at a light or get to my destination, it runs at least 3/4 on the temp gauge. If I step on the accelerator and bring the RPM's up for a few seconds it brings the temp down. It cause a cracked rad last week, and I really don't want to fork out another 100 bucks for a new one. Any suggestions?