2012 cummins fresh overhaul Temperature problem plz help.

One of '13 isx had a bad thermostat that had to be replaced. Cummins said they had a bad batch of t stats and alot are sticking. yours is doing what ours did.

 

Sounds electrical to me. If the temp gauge is truly bouncing that wouldn't be thermostats, they would be a gradual back and forth. Another indication it may be electrical is the other problems it didn't have before.

 

You will need to drain the coolant. You won't have to drain it all out, just enough to get the level below the t stat height. Remove the belt that is on the AC compressor. Once that is done you will need to undo the 4 bolts that hold the Air conditioning compressor to the mounting bracket. Remove the coolant hose going to the t stat housing. There will be 4 bolts holding the T stat housing into the block. Remove these. It will help you to have a swivel socket. I believe that they are 13 mm headed bolts. Pull the housing straight out as the t stat sticks into the block about 1.5 to 2 inches. Replace the seal inside, the t stat, and the gasket. Reverse procedure and then fill it back up with the coolant. To deairate the engine fill the surge tank back up as far as you can. Then run the engine at the highest speed that it will go. This will help get it hotter faster and get the air out of the system. Once the new t stat opens from the heat take the engine down to idle. Fill the surge tank back up. Run the engine another five minutes at high rpm to get the rest of the air out of the system. Put the cap back on and call it a day.

 

I think that it might actually be 15mm bolts instead of 13mm.

 

I am not sure if this will help you, check with the dealer
Looks like is made it by Cummins: