Quote Originally Posted by nonnieselman View Post
If your talkin about the truck in your signature the 07 NNBS and newer, it goes from open loop to closed loop at 102* ECT..

ON a 99-06 its at 131*ECT...

So thats not true.

I put a BB in my thermostat and i noticed no drop in gas mileage. ECTs stay around 170ish. Depends on Ambient Temp.
So I was curious to test this today. I was watching my wideband and aeroforce scan gauge so I knew exactly at what point it would switch to closed loop.

Sure enough when the coolant temp got to 131* it went right into closed loop. I could tell because the A/F ratio went from about 13.5 to 14.5-14.7 at exactly that time.