hmm I also have the headers and a high flow exhaust.... yes both o2 sensors are used to calculate air/fuel ratios. question we are trying to find out is how much with the 180 stat involved? I believe once the truck gets over a certian point around 170-175 its using the sensors to adjust as it should in a closed loop. thus It shouldnt really be harmful to the mpg at this point

 

it isn't harmful when the engines tune has been altered to sniff at 170~175*...

it is harmful when the OE tune is not altered to run off of that data before the engine reaches 190~195*...

there is not a decided OPEN and CLOSED.. there is a heckuva lot of fluttering back and forth.. it's not completely closed until the PCM agrees that operating temperature has been achieved.. a tuned PCM will make that decision cooler than a non-tuned PCM..

 

OK this has been proven then? because I seem to read a lot supporting both arguments... I have the stock tune (I believe) and haven't noticed any gas mileage increase or decrease since putting the 180 stat in 2 years ago...

 

this has been proven 'on my truck'...

I don't know about yours... it stands to reason the long term fuel curve can be altered via the PCM- and your truck learns that it's okay to trim fuel below expected operating temperatures.. as soon as you lose that data (power loss; disconnected battery) it has to learn it all over again.. short term, it's going to dump fuel.. long term, it just may figure it out...

if the hard scripted tables are altered in the first place, it won't dump all that fuel on you as soon as it reaches expected operating temperatures- which have been lowered via script/table..

like I said before- on my truck, it's almost like the PCM closes loop, re-opens it, closes, several times before it settles one way or the other.. It may or may not close loop before 190~195*, sniff the o2's, and log "well, that worked out, store this for later".. I don't know that.. I just know it starts to consider closing loop around 120*, then is usually closed at 140*, and only after flipping back and forth in the interval.. My suspicion is that it starts pre-positioning data for when the operating temperature is reached.

understand, though, this is just from observing this- it isn't a hard cold fact anywhere but in my head..

 

I retract my earlier statement. MPG not that bad with muddas and lower gears, really. At any rate, we will see what the MPG's do with the stock stat. Methinks it won't change a gnat's ***. But I've been wrong before. Ask my wife. And the
wife before her, too

 

drewactual, great post first of all.
i want to know what you think about my senario. I have an 06 magnum rt and just put in an 180* thermostat from autozone.

before the install, my average temp hovered over 227. now it maxes at 217, and hovers around 205-210.

i dont have any fan mods or tunes yet.

maybe i run hotter because i'm in L.A? how will running @ 205* instead of 227* essentially 20* cooler have a negative effect on my engine? or will it?

Thanks!