200℉ Cummins Thermostat

I've been experimenting with hotter coolant temperatures and found for most daily drivers this is a good way to go. The added heat actually will improve the MPG number just slightly and reduce EGT's slightly.

Gates - 34212 - 200℉

This is direct replacement number. It will fit into your 1998.5 to 2002 Dodge Ram Cummins 5.9L engine without any modifications.

Results

Summer operation floats right around 204 to 210℉ coolant temperatures. With the tuning I've done on Quadzilla the engine oil temperature will stay 30 to 35℉ cooler than coolant. This stays the same for even wintertime operations with no issues so far in one year of operation even towing. In the picture below I'm using the transmission sensor in the oil gallery at the oil filter. 

Why hotter?

Simply put the cooler you make the coolant the more the difference of temperature between the fire in the cylinder and the coolant will attract more heat energy back into the coolant wasting a percentage of power because of thermodynamics. The hotter you make the coolant the more heat energy there is for ignition of the fuel and don't require large amounts of timing to heat the fuel mist to a vapor to make it go bang. Remember liquid fuel doesn't burn till it is heated rapidly by compression and turned to a vapor now it will ignite easily. The other part is the less the expanding gases are cooled by coolant more power can be delivered to the wheels.