Let me share with you the observations after I did this Thermostat Swap to 4 cars, all have at least 5K since the change:
- During cold weather the coolant stays most of the time around 184F ±2F. Some exceptions if you are stuck in traffic when the coolant’s temperature goes higher since the “smart” ECM won’t start the fan so early.
- When is hot outside, over 100F, the thermostat works great, your coolant stays again around 184F most of the time! It is even better than in the cold weather because this time you are using AC and the radiator’s fan works very often, getting down the temperature. No issue if you are stuck in traffic, I never got the temperature over 190-192F and that only for a few seconds!
All 4 cars I changed behaved in similar way, I only had same issue with one in particular, until I did a better air flush to the coolant.
To summarize: I got the engine working temperature down from 221++F to ~184F, in order to avoid continuous overheating issue (the gauge is useless, it goes max to 185F, so you can boil the coolant without even know!). I didn’t see any MPG major fluctuation after the change. I never had issues with car warming up during the cold weather, nor overheating during the hot days and rush hours. I’m not going to argue about better engine performance at higher temperature, but this is not a racing car!
Ideally.... ideally I'll do the swap to a thermostat that would open at 195F-200F but the only one that fits and I could find is the one I mentioned into the original post. I didn't want to change the housing, add adapters, etc. If somebody can find a better thermostat, let us know!