So I get the error code for too low operating temp, it shows up occasionally, maybe 1x mo in the summer. In the winter very frequently, I replaced the inline thermostat w the lower temp, 180 I think it was.

Given its 90 degrees out, it seems that I should never get a low temp error in the summer. Leading me to believe that perhaps I have a defective coolant temp sensor. Am I thinking this is correct? The part is fairly inexpensive so I am not going to be too upset if the part does not fix the occasional code.

Side note, the last couple tanks of fuel I have gotten nearly 15mpg. From mileage over gallons filled. Historically I am 10.8 on average. Perhaps the faulty temp sensor is having the engine burn less fuel?

 

I am guessing you have an 03-04, the algorithim for the low temperature code is looking for the engine to reach a certain temperature in a certain time frame, if it does it three or four times in a row it sets the code. It is is possible if yours heats up slowing for some reason (like it it is idling a long time before driving off) or maybe if the thermostat element is stuck open it will set the code. It could be a bad sensor, I have had a couple go bad over the years, I usually doublecheck the obd2 temp with a small IR temp pen from Amazon.

 

I see the same codes pop up during the summer (over 100F here) but I installed a 170F thermostat. If the code is a big issue for you, run the AC. It dumps the excess heat into the cooling system.

But most importantly.... are there any other potential causes for your better MPG?????? I would love to know....

 

Interesting. What code are you seeing? My P38 throws a P0126 occasionally.

I've encountered some weird behavior using a genuine temp sensor and a generic Bosch.

 

Leaning out the mixture will make the engine run hotter, and I think significantly so to cut your fuel consumption by 50%! Not to mention I think you'd notice a pretty major power loss too. I don't believe the ECU can retard the timing far enough to compensate for that large of fuel deficiency in the mixture, it would knock like crazy. Any chance you've gone back to Super? I'd been running 87 for at least a year with what I believed were no real side effects, but recently I switched back to 93 and was surprised by how much mpg I picked up. It didn't go so far as covering the extra cost but I guess between new Nitto Grappler S2s, an OME kit and the roof rack I was chalking the lost mileage up to the truck and not the fuel. I'm back to close to 300m on a tank, up from about 240-250.

All that aside, it wouldn't hurt to swap the CTS in hopes it's contributing to the code but I doubt that would explain the huge increase in fuel economy.

 

I will cross the OBD temp with the IR temp on the radiator and see what I get. It sounds like it may not be a waste of time to put in a new CTS. I do get as high as 210, idling in 100 degree, humid weather. Ever since I switched to the lower temp thermostat I have been having issues. Maybe I just back to the original 180 that came w the kit? If I am not mistaken, there is no problem running cooler temps so long as I dont mind it taking longer for the heat to come on in the winter. Sounds like a fair trade.
As far as fuel, I general get 93 from Costco, the best fuel near me, no Sunoccos or similar. I think the long term 10.8 mpg is over years, same tires, not much else. I dont think anything changed, I am comparing a long enough sample to smooth out any anomaly's.

 

I replaced the coolant temp sensor yesterday, $20 for beck arnley. Seems to have fixed rhe issue. The code disappeared as soon as I plugged in the new one.

If you have a 22mm socket that is deep enough to go over the sensor. But not so tall it hits the intake you can do the job wo removing anything. Just a wobble and a 22. I pulled the alternator to get to it. Quick job.