The one that opened and closed most consistently around 180, purchased from 3 different stores as 3 different brand boxes but all motorads inside each
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box, all around 10$ each. I always test T stats before use, I bring them up to temp very slow and watch which one cracks first, get fully open first, and closes correctly then make a pick and return the others for refund lol.
Ah yes, the good ol' Motorad 4128! I have been using them since 2007, bet I've done at least 20 thermostat swaps. So I've never had a problem with them, but I feel like I read about a lot of failures on them over the past 2 years, saw some mentions of the Mishimoto so I thought I would give it a try. I think it was almost $50 too.
So the Motorad/Jet/whatever seems to hit 187-188, then settles to 185 after airflow and open loop mixing...the Mishimoto seems to open at around 177-178, mix for a bit, then adjust up to 185. I only threw a code one time over the years with the Motorad/Jet, did right away with the Mishimoto. Will probably swap back. I drive to work early in the morning and my car just gets up to operating temp by the time I get to work so I think I really test the code threshold.
Interesting/funny, one time with my Scat Pack around 2018 I went out to lunch with my boss and I was driving, it was summertime hot, had a Jet 180 in it. On the way back we were ripping around, A/C on, all the sudden I see my coolant temp gauge spike to 270! Limped the car back to work, called Dodge Cares, got it towed to the dealer and they replaced the water pump and tstat under warranty. Car ran fine after. Anyway, i always wondered if my tstat broke in the closed position then. Guess I'll never know...