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Old 10-21-2020, 11:39 AM   #1
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Fan clutch failure MBE926

Well this is going to be a longshot. Headed out on a trip on the 17th and got about 6-7 miles from home and noticed engine temps were climbing abnormally. I had just installed the BlueFire and it was its maiden voyage. After seeing some of the posts here where folks had odd issues I got pulled over and removed it and restarted the engine. Cooling went fine for the better part of 90 min where I was stopping to meeting someone and figured I had some weird issue with the BF. Fired back up after about 20-30 min and off we went with no issues. A bit later I pulled into a rest area and shutdown to stretch and review where we were going to stop overnight. Headed out and temps immediately started climbing again and this time I was able to get into a truckstop with temps approaching 230F and all sorts of alarms going off. I sat and idled for a while and did some investigating. Looks like my fan clutch was not engaging and was not getting any cooling. Temps slowly came down to a more safe range (<190) and I poked around looking for a blown fuse or relay. Both of which appear to be optional in a fuse panel per the diagram. I put a fuse in it and nothing happened so obviously not wired that way in this chassis. With it shutdown I rapped on the fan hub and anywhere else I thought it might help as well as unplugged what looks to be the wire to the fan and got it to engage. ..... So, question is.... has anyone ever changed out an engine fan electric clutch on a Mercedes MBE926 and what sort of fun am I in for? [edit] It's a rear radiator and will be changing belts while I am in there.[edit]

Currently we are 4 hours from home down in the Blueridge mountains of SW Virginia a bit south of Roanoke and will be nursing it and making sure the fan engages once it heats up to get it home where tools and parts will be available. I have tools and capable of repairing most stuff on my own. I will also put the BF module back on since it seems to not have been the issue.
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Old 10-23-2020, 04:23 PM   #2
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I don't know about yours, but some fan hubs have a place to install a couple of bolts to lock it up. Then it will run full time, but get you home.
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Old 10-26-2020, 04:47 PM   #3
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Well, we made it home with only some slight heating issues shortly after heading out. I re-installed the BF module before we broke camp and it was going ok for a while. The road out from the campground was mostly downhill and low speed. (40-45mph) I did see it heating up more than I was comfortable with and was able to pull over to check the fan which was not engaged. I shutdown and removed the BF device and fired her back up. I knew the road didn't offer much ahead for me to pull over into but I got all the way over to I-81N and the fan apparently engaged along the way. Temps got back into normal ranges all the way home. Now I am not sure if the BF device is part of the problem or not since the fan is managed by the engine computer.
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Old 10-26-2020, 05:02 PM   #4
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Normally when the fan clutch controller fails it should default to high speed mode. Most clutches disengage the high speed mode with either air pressure or electrical magnet pull. When either one fails they go to high speed failsafe mode and I had to have two clutches replaced that exhibited that behavior. They would lock into full speed mode and never go to idle. When high speed is disengaged in response to electrical signal or air pressure, viscous fluid in the clutch maintains a low speed turn of the fan. Usually when a clutch loses even low speed it's an indication the viscous fluid has leaked out.
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Old 10-26-2020, 08:41 PM   #5
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Whatís the downside of the fan being locked? Perhaps slightly less efficient?

My 2000 seems to have the fan spinning at the same speed as the engine...

It doesnt free spin...
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Old 10-28-2020, 08:57 AM   #6
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When my fan is not engaged it free spins due to being a viscous coupling but does not move much air. I would not put an obstruction in it to stop it but it does not spin especially fast. There is a 2 pin connector that I think triggers the lockup that you can see the wire in the image.
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Old 10-28-2020, 09:03 AM   #7
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Try this. With the engine off, try to spin the fan. If it move freely the viscous fluid has gone. It should have some resistance and it should move a moderate amount of air when in low mode. If it's not going into high speed mode when the temps rise to about 210f, the magnetic clutch is gone. The only cooling you may be getting is from air coming through from movement, not the fan. It really sounds like you need to replace the clutch. Below is what mine looks like and you are correct that the wire is what activates low speed mode as it should default to high speed.
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Old 10-28-2020, 09:08 AM   #8
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Quote:
Originally Posted by bpu699 View Post
Whatís the downside of the fan being locked? Perhaps slightly less efficient?
My 2000 seems to have the fan spinning at the same speed as the engine...
It doesnt free spin...
The only downsides are worse fuel mileage and noise. If it starts off noisy then quiets down, then the clutch is working. They start off in high speed mode until the viscous fluid reaches temperature then should slow down to low mode.
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Old 11-02-2020, 04:25 PM   #9
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Quote:
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Try this. With the engine off, try to spin the fan. If it move freely the viscous fluid has gone. ....

I finally got out to the RV on Saturday and tried spinning the fan. It does rotate but quite a bit of drag on it so I think the fluid is fine. If I unplug the 2 pin harness while the engine was running it made no change in behavior as far as locking up in any kind of failure mode. I did find out from my local NAPA that the clutch is a Horton 9905000 and I really don't want to have to buy one. They didn't have price but when I searched online I found them from about $650-800. :(


Do any of you know if that connector gets 12v when it is supposed to be engaged or if that is a "sense" line?
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Old 11-02-2020, 04:37 PM   #10
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Do any of you know if that connector gets 12v when it is supposed to be engaged or if that is a "sense" line?
That line should be powered when the fan is supposed to go into low speed mode. It turns off when it needs to go to high speed mode, which is the fail safe. You can try applying power directly to it to see if it affects the fan speed. If you check with an ohm meter, the fan internal should be 6-16 ohms. Here is a Horton troubleshooting document. Just FYI, the Horton clutch is what I have and had to be replaced twice in the first 20,000 miles (under warranty thank goodness).
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Old 11-09-2020, 07:27 PM   #11
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I checked the resistance this weekend and measured 6 ohms. I started out to take it to get an inspection today at 4pm and after it warmed up to temperature headed out. I got a little way down the road from the house and temps where just going up. Pulled off at a church to check the fan....not running. Turned around to go home and made it partway back before being forced with alarms about high temperatures to pull into a neighborhood to see about stopping for a while to cool down. Shutdown, poked around a little more and fired back up to keep coolant pumping thru the system....suddenly temps drop fast....go look and fan is running. Drove home. I did unplug the 2 wire connector in the driveway before shutting down...fan kept running. I donít get it.

Tomorrow I will call Freightliner and maybe Horton to get a better understanding of the fan system.
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Old 11-09-2020, 09:02 PM   #12
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It sounds like your temp sensor system isn't cutting the power when it should.

If it worked (locked up) after you had shut it down, the hub is probably fine. It's like most things mechanical, either it works, or it's broken.

Do like Lt Dan said, and unhook the wires to the fan and try it.
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