As the title says, I believe my thermostat may be stuck open. My 8 takes forever to warm up. For instance, it was ~26F this morning when I fired her up. I drove at a steady 60-65mph for like 20 min straight and the temp never got above 1/4. Then I stomped on it to overtake a slow-poke and the temp went up to the normal 1/2 mark. Then it dropped again to 1/4 after I cruised for another 5-10 min and stayed there until I arrived. This only happens when it's really cold out and only bothers me because I don't want to drive it hard or redline it when it's not warmed up. When it's warmer out it sometimes fluctuates a little but never this much.

Thx

 

N3H1-15-171 is the part number. its rather expensive, $41.90 list. kind of a PITA to change too, the alternator bracket needs to come off

 

So I'm correct in thinking it's the thermostat then? Well I would probably put in a RE-medy tstat from mazmart. They supposedly make it run cooler.

 

Sounds like the thermostat. Fix it quick because the warmup fuel trims can poison the cat, at least that's been my experience with other cars. Changing it is a pain, look at this DIY. Remember band-aids and beer.
https://www.rx8club.com/do-yourself-...cement-231160/

 

it does sound like a thermostat, not much else it could be

 

Alright thanks everybody, I figured it was. Will be putting in a new one soon