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Old 07-23-2019, 07:17 PM   #1
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Location: Mobile, AL
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Exclamation Freightliner/Cummins overheating

There is evidently a well-known issue with the fancy Horton Fan Clutch system failing early and often in Freightliner Custom Chassis RVs with Cummins ISB engines circa 2005-2014. Spoiler- Freightliner "Service Solution" 3737 gives their techs a specific diagnosis procedure to spot this endemic failure mode.

Random overheating, especially during the first twenty minutes or so of travel. You pull off the road, maybe shut down or let it idle or even rev the rpm with no load... after a while the temp starts dropping quickly like some kind of switch was thrown, indicating a sticking thermostat- right? On the cars/trucks we grew up with, yes, but this is an RV so we're not in Mayberry anymore.

There is a whole system dedicated to letting the cooling fan "feather" until the coolant temp gets above a certain threshold, which is ten or more degrees above the thermostat set point (I don't know the specific range, just talking theory here). So, from a cold start the engine heats up to around 190 degrees at which point the physical coolant thermostat opens up and, hopefully, the engine stays at that temperature. If, due to load/grade/outside temp, etc., the temperature climbs to, say, 200 or 205 degrees, the engine computer sends a signal to the fan clutch to engage the fan. So in a working system the temp should modulate from 190 to 205 degrees, with the thermostat limiting the bottom of the range and the fan clutch limiting the top of the range.

Apparently the fan clutch selected by Freightliner to pair with the Cummins ISB engines was a little flimsy for the task. The consensus (from trolling many, many forums) is that they consistently fail between 20K and 40K miles.

I had thought my engine was just under-engineered and I was doomed to sketchy uphill performance, especially towing my Jeep Wrangler (very lightweight toad). My overheating problems, intermittent at first, got progressively worse (more frequent), enough that I concluded I had a systemic problem. Due to the symptoms (rapid heating until something "triggered" and brought the temp down) I replaced the thermostat, easily accessed on top of the engine via the lift-up bed.

No relief. Enough searching and I stumbled upon a guy who nailed it, exactly describing my misery and pointing to the Freightliner "Service Solution" 3737 diagnostic bulletin.

There's your answer if you are having this problem. In the interest of brevity, I will end this post and follow up with the lesson(s) from my nightmare treatment at the hands of a Freightliner Service Center. If you need to get your fan clutch replaced, do yourself a favor and learn from my experience.
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Old 07-23-2019, 07:37 PM   #2
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Nightmare service, then resolution

So, there we were stuck 280 miles from home with the overheating problem so continuous that we couldn't go more than a few miles without pulling over to let it cool.

I phoned the FTL-HELP line (Freightliner Custom Chassis) and they directed me to a nearby Freightliner Service Center that was "Oasis" certified, meaning they had staff, equipment, training, and amenities for Freightliner RV owners.

This could be a long story, and it was a three day [Mod Edit] by any measure, but here's what happened:

I had to put my RV in a queue. Could not stay in it overnight. Could not drive 1/4 mile to Flying J and stay overnight there without losing my place in line. So, I sent the wife and dog home in the Jeep and took a motel room at $100/night.

I indicated the fan clutch had failed and referred the service manage to Service Solution 3737, wherein Freightliner acknowledges this failure and specifies how to troubleshoot.

He called me at the end of the next day with an estimate of $3,400.00 to replace the fan clutch. I knew the part cost around $800, and so told him no thanks, I'll limp home and find another solution.

He said in that case I could have my RV back after I paid $590.00 to cover their diagnosis. Which, by the way, told me exactly what I told him when I brought it in...

It took me ten hours to drive the 280 miles home. On a whim I called my local Freightliner Service Center (also Oasis certified) Empire Truck Sales, and asked them for an estimate to replace my fan clutch. Their estimate was $1,400.00 including parts. What a relief! What an honest business!

And shame on Birmingham Freightliner for their predatory treatment of this retired guy who they knew was stranded and bent over.
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Old 07-24-2019, 08:59 AM   #3
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This just happened to us coming back from Colorado, The temp would climb up and then drop back down for no reason on flat ground.
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Old 07-24-2019, 09:26 AM   #4
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Just be aware that "climbing" from around 180-190 and 205 is normal, i.e. working as designed. On my 2004 Cummins ISL, the range is more like 170-206.


Also, having the dash a/c on or off affects the range. With the a/c activated, the fan maintains a minimum air flow over the a/c condensor.
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Old 07-24-2019, 10:58 AM   #5
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Hi ! Welcome to IRV2! We're sure glad you joined the gang!

Noticed you are kinda new on IRV2 and wanted to say hello!

Good luck, happy trails, and God bless!
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