Engine is doing better after replaceing the thermostat and turning it around, it warms up faster and maintains a normal temperature, no more error codes. Now I will focus my attention on the transfer case which has a leak, I hate oil leaks, don't know if I will fix it myself or take it to the shop. I am not hearing any noise from it so I don't think it has damage. I do hear a bit of whine from the rear differential. The Jeep has 202K miles on it but not bad for a used 4X4, and I got it for what I think was a fair price.