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Old 12-24-2014, 06:24 PM   #1
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Cummins ISB 340 Engine Overheating Overheat Fan Clutch Thermostat Cooling etc.

I'm hoping to catch a wide range of searches with my weird title. I just want you to know that the ISB electric fan clutch, on a Freightliner Chassis is a known failure item in the 20 - 40 thousand mile range.

And, the symptoms are very consistent. You start up and drive a few miles - overheat. You stop, wait a few minutes, drive again and - overheat. Stop, wait, start again and magically the engine drops back to normal 194 deg range and runs the rest of the day no problem.

This is the classic fan clutch failure mode. DO NOT waste time with diagnostics. Just take your coach to a Freightliner dealer and reference Freightliner Service Solution 3737. That will give your dealer the information they need to diagnose this often intermittent problem. It's not a thermostat, it's not a dirty charge air cooler or radiatior. It's most likely a fan clutch.

You can also diagnose this problem by paying attention to the airflow from you radiator. When you start your engine, if you stand behind the radiator, you should feel a constant flow of air. Once you travel a few miles, if you get the overheat, stop and see if you have a constant flow of air from behind the coach. I'm betting you won't. That's a fan clutch! There is never a case, during normal operation, when your engine would be working hard or in a overheat status, when the fan wouldn't be operating in high mode. The fan clutch failure mode causes the fan to shut down instead of switching into high speed mode as the engine warms up.

You'll get to replace the fan clutch. It's a $1500 repair. While your at it, if you have more than 20K on the engine, you should replace the thermostat and the coolant. Another $500 but a wise move as the thermostat will fail eventually and cause similar problems.

The secret here is to point your dealer towards Freightliner Service Solution 3737 so they don't rack up multiple hours of diagnostic time looking for an intermittent problem. SS 3737 will give them the info necessary to diagnose the fan clutch problem without just running the coach through multiple cool/hot cycles.

Good luck!

PS: Make sure those diesel mechanics cover every inch of your interior in plastic / paper to protect the insides of your home / coach. Those boys aren't used to working on a diesel engine from the inside of a house. Ask me how I know!
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Old 01-09-2015, 05:11 PM   #2
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We had a similar problem with our 2010 Cummins/Freightliner ISB about a year ago. The coach was just out of warranty, but FL paid $2000 of the $3300 bill.

I'd play dumb, call FL tech support and just describe the problem and ask what they think. This is apparently a common problem, so maybe they can help you with the cost of this repair.

A little aside, it took Freightliner of Bakersfield, CA......33 days to get it repaired....a long story.
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Old 01-10-2015, 07:11 PM   #3
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Mine was $2700 - covered by FL. Back when these engines had slobber tubes, the radiators would get very nasty & plugged; I had a CAT 3126 do that. That is probably why so many respond with advice to clean your radiator.

If I were buying a used MH of this vintage with an ISB I would want to know if the fix has been done. Sounds like it is a fairly common (and expensive) problem.
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Old 02-19-2015, 05:17 PM   #4
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Been there, done that - X 2!!!!

We had the same fan clutch failure on our 2010 Winnebago Journey Express 34Y in the summer of 2013. We were leaving Great Falls, MT on the first morning of a 59 day, 6,000 mi. caravan through the Canadian Rockies & Yukon to Alaska. We no sooner hit the road than the temp gauge went to max. We pulled over & shut down, let it cool off, then started up and drove on to our first stop without further incident.)

Next morning, we headed out and again, immediately overheated! Reasoning "Cummins engine - Cummins issue", we went online & called the nearest Cummins shop (Lethbridge, BC). They said for us to try to come there. We limped into their shop, and the tech linked up with Insite and announced that our software was 9 versions out of date, and he didn't think we had "really" overheated. He thought the computer gave us a false alert and he could fix it with a software update, which he performed. Sure enough, we started up and it ran normal all the way to Calgary, where we met our group.

Next morning, we started out and - you guessed it! So this time we called the Calgary Cummins shop, who sent a tech out who put his PC on it & said it DID overheat. We let it cool down and were able to nurse it on in to their shop, where a long, drawn out diagnostic routine identified the electronic fan hub installed by Freightliner. So they ordered a replacement from FL, installed it, and 3 days/$4K later, we were on the road again and had no more cooling issues.

Fast forward to present day. We noticed when we left for AZ the first week of January, we that the fan, which after Calgary had run on high whenever the engine was running, didn't run til it came to normal operating temp. But it did run, so we took off. This went on without incident till Jan. 25 en route from Brenda to Quartzsite, AZ to have unrelated work done, and the temp started creeping up into unusually high ranges. We made it OK back to Brenda, but when we started back to Quartzsite the next morning, the temp shot to max & we were on the side of the road again.

We again let her cool down, then limped on in to Quartzsite, where "Diesel" Dave came out and tricked the fan into running by unplugging it from its dedicated control module. This allowed us to go on from there (with the "check engine" light on due to the disconnected fan) to Death Valley and Las Vegas.

We drove back toward Quartzsite, but stopped at a BLM area outside Lake Havasu City for the night on Feb. 2. Next morning, we got 10 mi. Down the road and overheated again. So we let it cool down, then limped back to Lake Havasu, where we were fortunate to find a guy who made some calls that revealed that the aforementioned fan hub was inherently unreliable. He recommended a non-OEM direct drive fan from a vendor in Oregon that was designed specifically for our application. We went with that, plugged the fan control module back into the harness to fool the ECM into thinking the old fan was still there, and voila - no more fan troubles.

But that's not the end of the story! The guy at Lake Havasu had ANOTHER owner with the exact same problem come in right after us. On this guy's coach, the plate to which the fan hub bolts was found to be loose. This plate is held to the engine block by 4 bolts, two of which were sheared off, one was about gone, and only one was holding on. Our guy called us & arranged to meet us where we're camped now to check ours - just to be on the safe side. He checked it today, and guess what! Only the bottom two bolts were intact but needed tightening. One of the top two was sheared off, and the other was on its way. So back to Havasu we go to get that fixed. The consensus is that the big, heavy OEM fan was more strain on the mounting plate than it was intended by Cummins to tolerate, and the torque just wore them loose.

So take it from me - if your diesel pusher is on a Freightliner Custom Chassis with a Cummins engine, you probably have this viscous drive electronic fan. If so, it's not whether it will fail you, it's WHEN. (Our first fan died at 26,000 mi, this one at 47,000.) So as far as I'm concerned, if I had one of these fans, I'd cut to the chase and preemptively replace it with a direct drive fan. And while they're at it, have 'em check that mounting plate!
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Old 02-19-2015, 06:17 PM   #5
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Quote:
Originally Posted by hawgguy View Post
Mine was $2700 - covered by FL. Back when these engines had slobber tubes, the radiators would get very nasty & plugged; I had a CAT 3126 do that. That is probably why so many respond with advice to clean your radiator.

If I were buying a used MH of this vintage with an ISB I would want to know if the fix has been done. Sounds like it is a fairly common (and expensive) problem.
ISB's don't have a slobber tube?...
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Old 02-19-2015, 06:44 PM   #6
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Thanks Randy for this information. I have a friend with the same issue. He says he has fought it for some time. I'll let him know.
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Old 02-19-2015, 06:59 PM   #7
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ISB's don't have a slobber tube?...
My 07 neptune with a 325 hp cummins isb has a slobber tube. Hangs down right beside of block on passengers side of rv.

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Old 02-20-2015, 06:06 PM   #8
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ISB's don't have a slobber tube?...
I no longer own the coach. It was my understanding that the along with more aggressive EGR and DPF, the slobber tube was eliminated. I could be wrong. However, I never noticed a slobber tube during my times underneath the coach.
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Old 02-20-2015, 06:14 PM   #9
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I no longer own the coach. It was my understanding that the along with more aggressive EGR and DPF, the slobber tube was eliminated. I could be wrong. However, I never noticed a slobber tube during my times underneath the coach.
You must have had the 6.7 litre isb. Mine is a 5.9 litre isb. When cummins went to the 6.7 litre was an emissions change and none of the 07 and newer emissions engines have a slobber tube. Sorry bout that I wasn't sure which engine you were speaking of.

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Old 07-02-2015, 06:41 PM   #10
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Randy,

What chassis do you have?
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Old 07-03-2015, 06:04 AM   #11
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Randy,

What chassis do you have?
It's a Freightliner Custom XC.
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Old 07-09-2015, 08:53 AM   #12
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The fan clutch bracket on my 2010 ISB 6.7 L broke while on the way to Forest City last July. It took out the clutch, the fan blade , and some other stuff. Cost about $11k to get back on the road 8 days later. Fortunately I had an extended warranty which paid all but $1800.
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Old 07-09-2015, 09:08 AM   #13
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My Horton fan clutch failed this January, with 22,000 miles on the coach. Managed to make it down to Key West & back though. Hope the new one lasts longer. :-/
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Old 07-10-2015, 09:36 AM   #14
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The fan clutch bracket on my 2010 ISB 6.7 L broke while on the way to Forest City last July. It took out the clutch, the fan blade , and some other stuff. Cost about $11k to get back on the road 8 days later. Fortunately I had an extended warranty which paid all but $1800.
WOW, talk about bad luck, I hope you got all the defective parts back.
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