If your OEM T-Stat is working fine, then I'd leave it alone. I tried 3 different T-stats, one cummins units, and two aftermarket ones and they all cycled horribly. I thought, "Hey the T-stat is 20+ years old...it should be replaced!"

Not sure why, but the new T-stats will stay closed until it gets hot, then open and cool things down, then close and heat back up. I couldn't stand watching that temp gauge constantly swinging back and forth.

I cleaned up the OEM unit...gave it a good fine brass bristle brushing, checked it in a pot of boiling water, then installed. Never had an issue since.

 

I just put a new head on my truck, got the tstat from cummins. My temp gauge doesn't fluctuate or anything. They have little nubs on them to allow water to pass through even closed. My truck warms up fine and doesn't get hot.


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I've got an after market coolant temp gauge and moves about 2 degrees while the OEM gauge moves about 10 to 15 degrees. With the OEM sender located on the drivers side of the engine when the thermostat opens cooler coolant comes out of the radiator and hits that sender first. My after market sender is mounted in the block close to the thermostat so it shows the actual temps in a more normal cycle.

Bob

 

I have a new OEM t-stat for mine, but only because mine is seeping from the seal.

 

The oem t-stat works the way it dose so it can slowly warm all the water in the engine and radiator than fully open. It can also close a little if it doesn't need 2 circulate as much water in colder weather. It basically keeps a steadier temp an unsteady water temp is bad 4 the engine.

 

Like others have said get a Cummins thermostat you'll have less problems.

Give them your engine S/N and CPL and they will give you the right one.

 

That answers my question. I am changing out the thermostat housing to a 2nd gen housing to run an intercooler and 2nd gen radiator. The original thermostat was not coming out without a fight and was damaged. Previous owner neglect. I have a 2nd ten housing on the way, and just need a thermostat and gasket to finish up that part of the head.

 

Make sure you purchase/use a 2nd gen thermostat and required (2) rubber gaskets. If you try to use a 1st gen tstat and gasket in a 2nd gen tstat housing, it will leak.

 

Will do, thanks for the info.

 

I called my Dodge dealer and ordered a thermostat for a 1995 Dodge Cummins. Am I correct to think this is a Cummins thermostat or can I only get it from a cummins dealer? I haven't picked it up yet, so I am not sure what it looks like or the numbers on it.

FYI: I am putting a new 7mm head on a first gen 12 valve engine, and adding an intercooler and 2nd gen radiator. I am also changing out the thermostat housing to a 2nd gen to get the radiator hose heading in the right direction. Whole swap is going into a 1969 K-20 Chevy.

 

It should be a cummins t stat if u got it from a dealer. You will know when u c it because the box will say cummins.

 

Sounds good.

 

I was just going to replace mine. Guess its normal and I will leave it alone.