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I am getting ready to pull my cooling system stand pipe of to get the new hydraulic wax valve nut welded on and to change a lower pipe and other elbows.

I was thinking of changing the thermostat while i have it opened up but i have looked all over for the correct one and i am having a hard time finding the correct part number for my 400 ISL.  I find 3 different part numbers at Cummins 3968559,3940632,5284903 not sure what is correct. I have 67000 miles on the engine and no problems with engine running hot but i havent been in the mountains yet and just drove it home 500 miles from Florida. Of course the fan was running wide open the entire time. So do you think i need to change it?  If anyone has changed theirs on a 400 isl and knows the part number i would love the info.

Thanks, Mike

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  • 3 weeks later...

I purchased an RV thermostat from Dometic when the factory one in my RV started going out. It replaced my old one perfectly and has been functioning very well for a month now. I love that this thermostat connects to both the air conditioner and the furnace. As you probably know, some models only link to the furnace, which isn’t ideal for someone like me who values convenience.

Edited by Dalton07
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  • 2 weeks later...
On 2/9/2022 at 2:22 AM, Dalton07 said:

I purchased an RV thermostat from Dometic when the factory one in my RV started going out. It replaced my old one perfectly and has been functioning very well for a month now. I love that this thermostat connects to both the air conditioner and the furnace. As you probably know, some models only link to the furnace, which isn’t ideal for someone like me who values convenience.

This thread is about the engine thermostat, not the HVAC type.

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