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Old 10-19-2013, 03:27 PM   #1
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Fan Clutch Control Options

I have all of the info for installing a Horton on/off fan clutch from other threads here and on other sites, including the need to get the CAT ECM fan control turned on. This thread isn't about the Horton on/off, but what I've uncovered about variable fan clutches.

I stumbled onto a BorgWarner Visctronic variable speed fan clutch that was installed on some C7 engines. My guess is that it was a city delivery or other straight truck setup. BW puts a lot of information out on their website about how to drive these clutches. Basically, the ECM puts out a PWM (pulse width modulation) signal that varies the lock-up of the clutch and therefore the fan RPM. Some systems even have a fan RPM feedback loop. I asked an engineer friend I worked with in the diesel truck supply chain about cobbling together a PWM controller based on coolant temp and he suggested that I first see if the CAT ECM can provide a PWM signal. Not what I was expecting, but his crystal ball was spot-on.

In the last two days I learned that in addition to the on/off fan control setting, most CAT ECMs have a Variable Fan Speed Option S for a Sauer-Danfoss hydraulic fan drive and a PWM mode. BorgWarner and Sauer-Danfoss both publish a fair amount of info on the web about the signal that their products need. BW expects a signal from 0 to 50 hz while S-D expects 40 to 100 hz. Interesting.

I'm taking my rig in for annual service plus a valve lash adjustment on Monday. In addition to the service, I'm going to get the ECM flashed (many updates since '04 and some of them were performance related) and a couple of parameters changed, such as setting the exhaust brake to "Latch". When that is complete, we will look at the fan control options. My engineer friend has an oscilloscope, so if the ECM tolerates having the fan control set to PWM or Variable Speed S without anything attached to the output, I should be able to get the signal verified in the next few days.

I have the Visctronic clutch that I picked up for peanuts, but the Big Three's heavy duty diesel pickup trucks are also using this technology. Mass production brings prices down, so there may be a cost effective solution out there waiting to be uncovered.

If anyone has additional insights, please post them!
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Old 10-19-2013, 09:40 PM   #2
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You will really like the latch mode, did mine a couple months ago. A can't believe I waited so long. Really makes it nicer to drive.
Regarding the variable speed fan, not only coolant temp but I would think a consideration to charge air cooling would also be a factor. I wonder if the ECM is smart enough to look at boost and intake air temp for the fan duty cycle. Would be nice if it works.
Another thought is to have a company such as Sorce engineering develop a new blade like they do for some Monaco's that runs at full speed but is much more efficient. Maybe if a large enough group showed interest it could be done.
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Old 10-19-2013, 11:19 PM   #3
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If the newer PWM fan clutches can be driven by the CAT ECM, that would seem to be the best solution. Completely variable fan engagement - no cycling.
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Old 10-24-2013, 01:29 AM   #4
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The latest software for my '04 C7 does not add true PWM fan control, which is a disappointment. I will proceed with my BorgWarner fan clutch working in the PWM On/Off mode.

As I mentioned, I had the valve lash adjusted. The service receipts I got with the rig when I purchased it were all from RV service centers, making me suspicious that the valves had never been adjusted. The tech that did the work said the clearances were all over the place, and that he only sees that when he is the first to adjust the valves after they wear-in. My rig has 40,000 miles of "wearing-in", and some of the valves were tight enough to have developed problems if I had tried to run it all the way to 100k. I didn't like the bill ($1100 for oil & filter, chassis lube, valve adjustment, ECM flash, parameter changes and some fan control exploration), but I'm sure that would have been a drop in the bucket vs. overhauling the cylinder head after burning a valve.
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Old 10-26-2013, 11:22 AM   #5
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I had my valves adjusted when I had a injector replaced at 28,000 miles. They had not been done since new. The tech said he could not improve on the settings he found.

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Old 10-26-2013, 02:17 PM   #6
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I really think that some RV entrepreneur should put together some type of Fan system. It does require some engineering. Source Engineering could easily build a flex fan like the one they make for Cummins /Monacos. I contacted Horton and they would gladly do something but Cat will not give them the engineering data that is required. When we had our Bluebird the Horton fan would use 45 HP when engaged!! That is a lot of power and fuel. A clutch type fan would make for a quieter engine, more power and better fuel mileage. Probably just as good as any chip one might install! I do know that when Cat's were still being used by FL they did develop a system using Horton Fans. It was experimental and the few that were installed failed in a short period of time. FL does have a clutch type fan on the small block Cummins.
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Old 10-27-2013, 01:51 AM   #7
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1) Are you sure there were a lot of failures? I believe the guy that spearheaded the Horton installation in 2004 still has the rv and still has his Horton fan clutch. Horton has a good reputation in the industry (I worked with a quality manager that we recruited from Horton) so I would be surprised if there were failures of the Horton clutch. It seems like the rest of the system is just too simple to be a problem if installed correctly.

2) Truck parts are low volume and expensive. I suspect a large percentage of owners don't want to be involved beyond handing a credit card to the shop that does the install. I think the bill will easily be over a grand, probably closer to $1200. That puts payback in the 15k to 20k mile range.

If the PWM clutches being used on the big diesel pickups have the torque rating to swing a fan for a rear radiator RV, there might be hope for a cheaper solution. Having the radiator out front in ambient air makes the job a lot easier, so those clutches may not be up to the task in a rear rad installation.
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Old 10-27-2013, 07:28 AM   #8
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mbrandt: If you go back into the archives of the Yahoo Cat forum there is a thread where FL removed the clutch fan from a unit due to multiple failures. I think that is when they gave up on the project. You are correct that Horton makes a fine unit but perhaps there was a problem in this application. I also do not know if FL installed the same fan as those owners that did the job themselves. I will be following your project with much interest. Does the Cummins rear rad setup use a Horton or some other system? Our Bluebird front engine MH had a Horton with an override switch. When I engaged that switch I could watch the temp gauge drop. Noisy but awesome.
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Old 10-27-2013, 10:15 AM   #9
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If Cat refuses to provide the needed engineering data to build a clutch or variable speed fan for their engines I can't imagine anyone assuming the legal responsibility to build one. Talk about sticking your neck out!

Before attempting to adapt one from a front radiator pickup finding the horsepower rating of those devices would seem to be the first item to investigate. My guess is they will be rated for half the required power to drive the fans we have.

Has anyone looked into adapting one of the hydraulic fan drives used on the side radiator coaches? Big bucks I am sure!

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Old 10-27-2013, 12:41 PM   #10
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jauguston: Last year when I spoke with Horton I was really upbeat. The engineer said all he needed was some data from cat and he could then recommend a suitable fan. I think all he needed was the necessary air flow. The frontal area is easy to attain with a tape measure! looking through some old posts on the FL forum I se where in 07 others tried to get the info from FL on the fans that were being used from the factory. No Go. FL said that those fans needed 1050 sq. in. of area and apparently that person had a MH with only 1000!!! But I did find a post from a person who had FL install a fan and he had lots of problems. I am beginning to wonder if there is something wrong with the design of the rad pack and shroud. I was thinking of all those fan hub bearings that are bad. Could it be that the heat in that area is very high? The rads are all packed in very tight. On our 02 Bounder with a Cummins there was room between the rads to easily clean them. I also don't think the shroud was as restrictive but that was 5 years ago so I cannot be sure. Cat and FL are just playing CYA. They both have all the information we would need.
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Old 10-27-2013, 09:01 PM   #11
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The location of the fan hub bearings is right on the front of the engine block behind the fan. With a pusher fan there is no radiator heat there.

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Old 10-27-2013, 10:56 PM   #12
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JIm: I am fully aware of the rad location and the fan hub location. BUT maybe there is engine heat in that area that kills the fan hub bearing. Why does the C7 have such premature failures of that bearing? Is it undersized? I don't think so. There has to be a reason and heat came to mind right away. Surely every fan blade is not out of balance and kills the bearing. Heat was just a thought.
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Old 10-27-2013, 11:47 PM   #13
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you could get a Arduino and make your own

some line of code and set it up your self

one thing i would see is set it for low mpr if at low temp to slow fan so your not sucking up trash off the road at redlights as long as your temp is low and can be ok at lower rpms

but truth be told i would just have the fan on at all times as the motor is not the only thing that runs hot and that why alot of the GM 8.1l like to run hot in the UFOs
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Old 10-28-2013, 01:26 PM   #14
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At last, some useful debate!

I'll try to find the thread with the failure.

CFM: what we have works. If we can find a part number on the current fan, the company that molds the fans will know what to supply. If I can adapt my current fan and maintain perfect balance, I'll simply do that. There is some slip in viscous clutches even at full lockup, but I know I have headroom in my cooling system. The needle doesn't really move even on a long climb.

Pusher orientation: I was bothered by this at first. However, look at how the Horton clutch works - it doesn't see enough heat in the pusher orientation to trigger the viscous fluid, so they added a heating element. I think we can rule out heat killing the fan clutch.

Fan bearing - Most of their engines are installed in devices that get professional maintenance. IMHO very few RV centers qualify as professional maintenance on diesel pushers - at 40,000 miles my '04 had never had the valves adjusted, but had been to a big RV center every year. Could a fan clutch lessen the load on the bearing? I think so, and maybe the truck use of the C7 most often has a clutch? Those engines see a lot more miles than ours, and fleets have been tuned-in to fuel mileage for a long while.

I agree that the pickup truck fan clutches probably would not get the job done, but for the rest of you guys (I already have my clutch, salvaged from a front-engine C7 Freightliner M2 Business Class), I'm hopeful that the economies of scale for the pickup clutches might bleed over to the heavier clutches.

Arduino - I'm barely aware of these, but unless they could tap into the CAN-Bus, they would have to have their own sensor(s). I will investigate further, as I like the thought of having a truly variable fan drive. The ECM's "fan on" signal would be an input to the arduino. I would want to retain stuff like locking the fan when the exhaust brake is engaged. I don't think my a/c condenser is in the heat exchanger stack at the rear of the rig, but if there are any that do have it back there, the ECM also watches for a/c system pressure and kicks the fan on.
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