Thermostat ?

[Jackpine]

Originally Posted by BlackSTX

That was a concern I had, the old GM-OBD systems had a set temp before going into normal operating mode, if I recall correctly, it may have been around 165 degrees. I have been monitoring mileage, and so far it seems like it's consistent, though I'm sure temps doesn't have to be significant for the PCM to enrich the a/f mix. My only real concern is going too rich for the cats, since no one wants to have to replace a set of cats.

Yup - I forgot about the cats. They suffer too. You'll probably be operating open loop longer after a cold start. But again, once the thermostat is open and the coolant temperature stabilizes, you're really just about back where you started, except that if it's really cool out and you don't put much load on the engine, you might be running colder than you really want, since the "floor" is lower.

- Jack