Cummins 3946849 Genuine 190 Degree Coolant Thermostat

Top end quality for 5.9 Cummins!

My truck was getting hot, figured I would start by replacing the thermostat, sure enough, it took care of my problem, temp doesn’t budge past 190 and stays in the 175-190 range all the time now, highly recommend!!

I bought this thermostat thinking it is the right one for my Ram 2500 with the 5.9L Cummins. After checking back with XDP, I was told that I need this different one, which runs at 180 degrees. So I ordered the one they recommend and installed it. Sure enough, the temperature hovered right around 180 degr. with the "correct" part. However, in researching the topic a bit more I found out that the 5.9L Cummins, or any other diesel for that matter, runs best at around 200 degrees, and has the best fuel efficiency. So I took out the one that was recommended, installed the Mishimoto 190 degree thermostat I had previously ordered and - the temperature is where it was before, right around 190 degrees at light duty driving. I am not sure why they sell the 180 degree part for that application. The old one I took out also said 190 degrees, and I'm happy I kept this one.