Thermostat Question

[bayman1975]

Has anybody changed from a 195 degree to a 180 degree thermostat, and notice a drop in fuel mileage? Just curious. I've not changed mine yet, but we used to see that in the past when it was done. Thanks.

[yuppiexj]

I made that mistake. lost 1.5-2 mpg...my understanding is that the ECU will never get into closed loop vs. over-fueled warmup mode.

Changed it back and all was back to normal... unless you're running a blower with 14psi of boost and/or running super hot, I would leave the stock temp in there.

Buy a good one (not the cheap Stant... they have a better one)

[gradon]

Well, when I started the trip to Penn on Thursday, I had a 180* in there. My Dad wanted to use the A/C so we went to his buddies house and he charged it up(wasn't sure if it was low--it was a little but the 97 ecu still won't engage the a/c clutch). We alligatored the a/c clutch wire to the batt and 15 miles later it was overheating. The radiator and reservoir were full of coolant. We popped the thermostat out and the block was empty of coolant. I happened to have a new 195* t-stat in the console and we popped it in. Dad dropped the lower t-stat housing bolt twice--the 2nd time it was stuck behind the idler pulley. He recommended a quick turn of the starter to get it out. Then we didn't see it. Pull out aux fan, belt, and pulley and bolt is nowhere to be seen. Look for 10 minutes--oh well favorite JY is 6 miles away. Drive to JY and get bolt for the $1 entry fee, buy $1.75 gallon of recycled anti-freeze. And drive 200 miles to State College area w/o probs(t-stat housing didn't have new sealant). There I bought fresh coolant, sealant, and a new 16# cap(other would let coolant into reservoir at the boiling pt). Anyhow drove back today and it stayed b/t 195-200. I've heard that the changover pt between warm-up loop is 160*, so a 180* should be fine, but who knows what obd2 thinks. I did record the best mileage in a while with getting 315 miles out of 16.75 gallons=18.8mpg for 95% highway use(up and down PA mts @ 60-75mph), so maybe the extra 15* helped(although I had the aux fan disco'd from ecu to be on constantly so the ecu currently thinks it's -40*C). I did note that a 4.7K resistor jumped across the CoolantTS makes the aux fan cut on at 215* instead of 230*(dino has a good writeup on his site), but I didn't even want it to get to 215* with the way the old cap was letting the coolant bubbling over. I also note that the aux fan blows the hot air from the radiator into my K&N filter even with the shield(there's a 1-2" opening there), so I will be completely isolating the intake from the rest of the engine sometime soon. Anyhow I do feel better about the 195* in there now. I went with the 180* at first to help control detonation on a fresh built engine(it has 2K now).

[jeepinwi]

I've been running a Super Stant 180 thermostat since day one, and my mileage is 18-19 mpg consistantly. If my guage is correct, the engine runs 190-195 regardless of outside temperature. I also have a 00 XJ which is bone stock(195 thermostat), and that engine usually runs about 215 degrees. In my opinion, that is uncomfortably warm.