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Old 09-23-2019, 08:11 PM   #1
Join Date: Jan 2019
Posts: 32
Thermostat . . . wow

I am in the process of replacing my aged plastic surge tank with newer metal version. Also doing coolant change (to Final Charge OAT) and decided to replace the thermostat because I was uncertain of its age (it was working fine). It turns out the thermostat was original to the engine. Though it was working fine, I literally had to heat and beat it out of the housing! Amazing. Lots of crud and build up and I am not sure how it could have gotten that bad. Almost looked like carbon build up. Coach has 64,500 miles on it, with ISL400. Engine runs good with no known issues. Anyway, got the housing all cleaned up and reinstalled with new thermostat.Flush and fill tomorrow. Thought I would show you what a 14 year old thermostat looked like.


2006 Thor Mandalay 40B
Cummins ISL400
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Old 09-24-2019, 11:30 AM   #2
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Carbon in the coolant...doesn't that mean you have a bad water jacket gasket somewhere? I had a 5.9 Cummins and there was a little oil floating around in the coolant a shop showed me once. RV was 14 yo at the time. Did some research and discovered that Cummins engines were well known for having a small leak between the oil pump and the water jacket (straining my memory here). I never bothered to repair it as it never grew worse. Sold it when it was 22 years old. Still wasn't any worse then when I first became aware of it.

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Old 09-25-2019, 06:41 AM   #3
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If you still have it, check and see if the black material is magnetic

Looks as if the corrosion inhibitor levels could have been low

Great thing to have caught and replaced
2016 Tuscany 42GX
F150 KR or Escape Toad
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