I live in york pennsylvania and everyone round here will understand the change in temp lately well since it got cold I've noticed a huge drop in my fuel mileage. Out on the trails in the summer my jeep would run too hot for comfort so i put a 180 degree thermostat in which kept it at a mangable temp. But it doesnt even get to operating temperatures now. (205-215) I noticed on our shops scan tool that the o2 sensor was showing richer than it should have been and my coolant temps around 160-170. So i put a peice of cardboard in front of my grill to prevent the radiator from working too efficiently. My coolant temp is perfectly in range and I went from 13ish to 18 mpg backroad and city driving on 31's with 3.07 gears and 242 thousand miles on my 4.0 5spd cherokee with a bit of extra weight. Just a thought for everyone else who noticed a signifigant drop in mileage. Sorry if my spelling made that hard to decipher haha

 

lol I get 12-14mpg on 31s. If I keep my foot out of it when its cold I actually get up to 17 but with a cowl snorkel and 20 degree outside air, romping on it is so much fun

 

Don't forget about winter gas here too. That drops mpg down

 

I don't understand how a 180 t stat raised gas mileage..

 

curious how the op is calculating mpg

 

The 180 thermostat keeps the engin running cooler but it wasn't even getting to operating temps now that its cold. The engine runs richer until its warmed up so I was running rich all day long. I calculated my mpg by filling up running till the light came on then refilled and divided the miles traveld by the amount of fuel the second fill up took

 

I get 13 when I romp on the pedal with 33s lol

15-16 normal driving.

 

Putting the cardboard over the grille raised the mileage allowing the vehicle to get to operating temp as it was not doing so with the 180* t-stat in the winter weather.

 

Yea I have like a 165 thermostat. I run 195 degrees most of the time when im driving. Once it goes to 205-210 my coolant boils,

 

Sounds like you are running a bad mix or your cooling system isnt holding the correct pressure.

Water boils at 212°. So a 50/50 mix at 16psi should be round 240.