I have started to take stuff off my truck in preparation of putting my new heads on. While I am at it I thought I should put a new thermostat in. The last time I replaced it years ago before I gained so much knowledge thru FTE, the parts guy asked me which one I wanted. I picked the lower temperature one thinking it will make my truck run cooler.

Then I learn that engines should run hotter to burn off stuff better. So should I buy a T-stat that opens at a warmer temp this time? The shop manual lists two types. The standard is the one that starts opening at 152-157° and is fully open at 177°. The high temp one starts to open at 167-172° and is fully open at 192°. Which should I buy? This is for my 54 F100 with a 239 Yblock.

 

Put the higher temp in, Abe. I think the low temp T stat was used for alcohol based antifreeze.
Edit: I ran 180 deg in MG.