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Old 11-20-2019, 04:59 AM   #1
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Join Date: Jul 2014
Posts: 393
2003 ISC-350 Coolant Types * Flush Questions * Parts Replacement

My 2004 Itasca "Horizon" 40AD has a 2003 Cummins ISC-350 and I just passed the 100,000 mile mark.

I called Cummins with my SN engine in hand and they said my engine came with OAT coolant. They said it was designed for the life of the vehicle. (My coolant is green. And I don't think the previous owner changed it.)

I... on the other hand, changed my anti-freeze filter 3 years ago (30,000 miles ago) when the damn thing sprung a leak out the bottom due to a rusty hole. (Caught it one morning during a walk around check... before I headed out of a rest stop.)

At that time I brought my RV to a great RV repair shop in Branson, MO (with an amazing RV lift) and they changed the filter and tested the PH. Everything checked okay so they just topped off the coolant tank.

Last year my plastic tank cracked and I was forced to use 4 tubes of JB Plastic seal I got from a Highway Truck Stop (worked great); and then I added about 2 gallons of bottled drinking water to get me to the next Freightliner shop. (TIP: You people heading to Alaska this season should carry at least 3 tubes of this plastic weld with you! And a 36" battery cable I used after my bad alternator left my ECM running on the current left in my engine battery... until it dropped below 10V. ...And that battery cable jumper-ed to my house batteries allowed me to drive another 100 miles! So I hope everyone carries one of these now that you have read this story!)

At FL we changed the plastic coolant tank; and alternator; and they refilled the reservoir with green coolant compliant with Cummins specs.

This year, I started to notice my engine temperatures climb to 220F up a Moab grade when it was 105F outside. (So yes... my AC was on high, and I was also towing a Saturn Aura.)

In the past, my engine never got this hot! (Same conditions.) And she's been running great and with normal temperature ranges ever since the Moab grade. ~4,000 miles now.

However, I'm wondering if it's time to flush my engine & radiator and change the coolant in spite of what Cummins tells me the OAT coolant is designed to last... plus replace other parts: Thermostat, hoses, clamps, filter, ???

I have never changed my radiator hoses or those heat exchange hoses connected to my Atwood 10 gallon water heater; and my thermostat his original.

I know there is the simple flush I can do... but I'm thinking I should do much more so I can drive trouble free for another 100,000 miles... in this world and in my next life!!!

[B]What would you do? What type of flush solution would you use? ...Knowing I have had OAT coolant now for over 15 years?

Would that imply I don't have any silica buildup in my radiator, because I have had OAT running all this time? ...And does OAT extend the life of my hoses for the life of the engine?

It's a fair question: How can Cummins claim OAT will last for the life of the vehicle (some say 300,000 miles) unless all these parts are also good for the life of the vehicle?

2004 Itasca Horizon ISK-40AD, ISC-350HP Cummins
... and the best of 3 Diesels I have owned thus far!
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Old 11-20-2019, 05:31 AM   #2
Senior Member
Join Date: Jul 2014
Posts: 393
Please Only Comment If You Know What OAT Is & Have Personal Experience With This Type

Cummins ISC engines come from the factory with different coolant types. Many ISC owners need to monitor their coolant closely, because they are not running OAT.

Consequently, I respectfully ask people DO NOT to reply with general "hearsay" type answers about other coolant flush techniques; or how they would replace all these parts I mentioned just because I have 100,000 miles on my coach. I'm more concerned about 15 years of life on those rubber hoses.

For example: Do radiator hoses wear from the inside out? Do hose last a lifetime if you run OAT coolant?

Respectfully, I hope we hear mostly from owners who have had personal experiences with OAT coolant in their engine and experienced component failure and/or high temperatures in their ISC/ISL engine; or...

...has relevant information to share and can speak to cooling systems as a whole; and/or what the proper maintenance schedule applies for us owners with OAT coolant in our ISC/ISL?

Thank you!
2004 Itasca Horizon ISK-40AD, ISC-350HP Cummins
... and the best of 3 Diesels I have owned thus far!
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ace, parts, replace, replacement

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