how do i know if i forgot which direction the thermostat goes

spring side towards motor. does your cooling fan work at idle when it starts to overheat?

If you made sure the direction of the therm is correct, did they give you the correct one at the parts store? The therm has to have a small pintle on it and it has to be installed exactly the way it came out. Not sure how is goes back in, as I have not done mine as yet(will be doing in 2 months with a lower temp unit). Check eHow and youtube to see if there is any further info that can help as well as PT forums(just type this in as a general search engine).