my thermostat was replaced about 6-7 years ago. Ok so this doesn't happen all the time, but once in a while when the truck is still warming up and getting to about the 200 mark that it runs at normally, I will glance down at it and it's well past that about to 240. Then it stops and quickly goes back down to 200-10 where it usually is at. I should have changed it out when I replaced the waterpump a year ago but it didn't dawn on me until after. I'm sure this thing is on it's last leg right? What's the big deal with using 170 or 180 degree thermostat's on these motors? I see that most with chips and whatnot that require one of these to be installed.

 

It sounds to me like your thermostat is starting to stick shut. Being that they are only a few bucks I would swap it out with a new one. I think the big stink about the 180 t-stats is that your engine gets up to running temp faster and our engines run better being a little cooler. When I replaced mine about 2 years ago I swapped it out for a 180 and now once its warm it sits right on the 180 point on the dot. It gets up there relatively quickly too.