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That looks like a reboxed NAPA thermostat at first but now it slightly different the jiggle pins are in the outside on the Cummins, where the NAPA one looks slightly wider mouth and flows more coolant. You can see the newest design to the right on the photo below. The two in the middle were the design closer to the OEM design MotorRad but these are still NAPA thermostats. Then the Gates thermostat on the left which is like the NAPA in design but that one is a 200*F thermostat but it failed in mere 2 weeks wild swings 170 to 230*F never settles.


Personally I suggest the NAPA 180... It will look like the right one. I'm using a NAPA 190*F and ran all the way to Mohave Valley AZ towing my RV there and back NEVER had one issue with coolant temps ever. The transmission was getting hot from all the EGT heat in the exhaust. Even my screwing around in the desert and slow crawling never had a single issue with temps even hovered at 195*F typically even with temps in the 118*F and A/C running. 

OEM & Aftermarket - General Conversations - Mopar1973Man's Dodge ...


My trip to Oatman, AZ to wonder the desert on Hwy 66...


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From what I have experienced and researched the one with the larger opening is for the 12 valve. I have installed 2 different ones and also got up to a 40 degree swings from them. I was at the local Napa just one week ago and they could no longer find a 24 valve thermostat with the small opening. They list the large one for all 2nd gens. I did find the correct one at Advance auto by Stant.

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