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Foretravel Motorhome Forums => Foretravel Tech Talk => Topic started by: mikerox on April 27, 2025, 08:48:37 pm

Title: Thermostat source
Post by: mikerox on April 27, 2025, 08:48:37 pm
Planning on replacing my thermostat when I replace coolant. Cummins wants $75 for a new one, should I go with an aftermarket one, Napa couldn't find a cross reference on the part # but I found one online from Highway and Heavy Parts $17. Big difference, but I don't know if I should stray from OEM parts for something as important as a thermostat? Thoughts?
Title: Re: Thermostat source
Post by: Realmccoy on April 27, 2025, 09:36:22 pm
I would go OEM, that's not a cheap engine.
Title: Re: Thermostat source
Post by: mikerox on April 27, 2025, 09:52:11 pm
Real McCoy thanks, I sent you a message concerning a previous post
Title: Re: Thermostat source
Post by: Dennis H on April 28, 2025, 10:14:42 am
Planning on replacing my thermostat when I replace coolant. Cummins wants $75 for a new one, should I go with an aftermarket one, Napa couldn't find a cross reference on the part # but I found one online from Highway and Heavy Parts $17. Big difference, but I don't know if I should stray from OEM parts for something as important as a thermostat? Thoughts?

Aftermarket thermostats can become a tricky situation especially for larger engines. In addition to the quality concerns there often design differences. The aftermarkets parts listing, cross references, are often based on the top body diameter, secondary disc if applicable, and temperature rating. Often the operating disc size or type are considered. This is real common problem in the RV gas engine world as almost all over the counter thermostats are actually the wrong disc design for the larger radiators and increased coolant flow that all those engines have compared to the vans and pickup truck. The other unknown is the operating characteristics of the stat. At what temp does it start to open and what is the difference in temp from opening start to full open? What is the response timing. What is the Hysteresis for it to begin closing. You may not see or notice the difference, but you may also get one that contributed to that spread where outside temps and load tend to have an effect on the running temp.  The engine that takes forever to warm up as the stat cracks open too early and then runs hotter than normal under heavy load as it doesn't open fully when needed. Changing a stat sometimes can became an experiment. Even with the OEM one. Sometimes there are also air bleed or bypass features that may be missing or may be there and not desired for the application.
My thought is that if you can easily change, you can go for the aftermarket. You do want to look at it carefully and consider where it came from. Compare it carefully with the one that comes out. As for the price difference, if Cummins is still supporting those older engines and providing even commodity parts, that needs some support. If we don't buy, at some point they won't provide.
Title: Re: Thermostat source
Post by: MarkC on April 28, 2025, 09:44:01 pm
Go with the Cummins. It's cheap peace of mind. You won't regret it.
Title: Re: Thermostat source
Post by: oldguy on April 29, 2025, 10:34:33 am
I have only ever had one thermostat fail and it was a from Cummins and they usually fail open.
Title: Re: Thermostat source
Post by: dsd on April 29, 2025, 10:40:09 am
Im confident what ever you replace it with wouldn't provide the service life yours has unfortunately. I would go Cummins OEM if I was replacing.
Title: Re: Thermostat source
Post by: dsd on April 29, 2025, 10:46:56 am
My thought is that if you can easily change, you can go for the aftermarket. Compare it carefully with the one that comes out. As for the price difference, if Cummins is still supporting those older engines and providing even commodity parts, that needs some support. If we don't buy, at some point they won't provide.
Everything here is exactly correct but I wanted to highlight the above .
Is it easy to change on the side of the road? How much coolant will you loose
Cost of replacement coolant.
Cost of tow?

Starting to make that overpriced part look cheap once you  include all the multipliers to its replacement.
Title: Re: Thermostat source
Post by: kgrover on April 29, 2025, 05:37:17 pm
I tried a cheap one from Amazon and it didn't work right, it wasn't long enough to seal at the lower end and block coolant flow. I ended up going to Cummins to get the right one. The part number had been updated multiple times with improvements since the original was built.