Originally Posted by 6.boom
Over the past week and a half my ECT's have been a bit lower than normal. It normally is around 186-190ish range. Now its 180-184. According to my insight my average mpg (i do mostly city driving) is 13. It has dropped down to 9. I am not missing coolant, and it is running fine. It has been getting colder, but not enough to affect my ECT temps. Am i just being paranoid?
Sounds like your thermostat is getting week, as in these trucks they fail open as a safeguard. Running around unloaded, ECT should be around 190 to 195f, where the thermostat begins to open. And engine temp is tied to fuel mileage - particularly with diesels. The ideal temp for diesel efficiency is 203f.
Also, some states may already be switching to winter blend diesel, so prepare for the annual 2 - 3 mpg drop to begin