Fan Clutch Operation Details

[calbiker]

Got a friend that installed one of those. It didn’t get to 1.4 ratio.

 

[Midwestdrifter]

Got a friend that installed one of those. It didn’t get to 1.4 ratio.

You are possibly right, but aside from buying 5 samples from 5 different brands (25 total), and testing them, do you have a reliable suggestion? Cause no single brand or source is repeatable at this point.

At idle and locked I was seeing just under 1,000rpm, which while not 1.4X, was still something.

 

[Midwestdrifter]

Anyone tried this style with blade recently? Looks to be the aftermarket version of the unit used on the MB I4 on the NCV3 (which is phyiscaly a similar size to the T1N version).

 

[sugawi]

Anyone tried this style with blade recently? Looks to be the aftermarket version of the unit used on the MB I4 on the NCV3 (which is phyiscaly a similar size to the T1N version).

View attachment 271851

I have been using this one (from Autozone) for the last year and it works great without issues. Keeps temperatures about the same as original before that one was failing.

 

[jrod5150]

Anyone tried this style with blade recently? Looks to be the aftermarket version of the unit used on the MB I4 on the NCV3 (which is phyiscaly a similar size to the T1N version).

View attachment 271851

haven’t had any issues with them. They are much quieter when they lock so you really have to listen for it, Haven’t tried the Chinese version only the German ones.

 

[Midwestdrifter]

haven’t had any issues with them. They are much quieter when they lock so you really have to listen for it, Haven’t tried the Chinese version only the German ones.

The annular ring at the blade tips makes them a fair bit quieter I would guess. Also a bit more efficient.

 

[jrod5150]

The annular ring at the blade tips makes them a fair bit quieter I would guess. Also a bit more efficient.

I can ship you out a German one if you’d like

 

[Lojack72]

Anyone tried this style with blade recently? Looks to be the aftermarket version of the unit used on the MB I4 on the NCV3 (which is phyiscaly a similar size to the T1N version).

View attachment 271851

Yes- installed one June of last year per https://sprinter-source.com/forums/index.php?threads/12364/post-1207550
It's been keeping up with the South Florida heat this summer, so can recommend.

 

[calbiker]

From the discussions here, a year ago I suggested to my friend that he install the Autozone fan clutch on his Sprinter motor home. I installed a tach in his vehicle to measure fan rpm. I believe it maxed out somewhere around 3000 rpm. I've seen 4400 rpm on my stock fan, and fan speed can likely get higher if engine rpm increase.

The reduced speed is probably OK for most users. It could be an issue for Sprinter motor homes.

 

[michaelyares]

Thought that had been done to death but seen as you mention it...
View attachment 183985

Is the vertical thing unique to the sprinter? In any event I forgot and laid mine flat so time will tell.

 

[Cheyenne]

Is the vertical thing unique to the sprinter? In any event I forgot and laid mine flat so time will tell.

To the best of my knowledge it applies to all none electronically controlled viscous clutches.

PS If it was only for a few minutes or maybe an hour or two you may be okay, anything longer and it would be interesting if you kept us updated.

 

[smcguyer]

I have two clutches, both used, both from Europarts, about a year apart (last one was ordered a year ago or so. Neither clutch has ever made the obvious roar or lockup, we don't spend too much time in hot weather, and I just drove to keep the coolant temps reasonable most of the time. It was really only an issue when running at 100% load for more than 10 minutes in hot weather.

I took both clutches apart as far as reasonable. Despite being different brands, both probably came from the same factory. The brass pin/rod which controls the locking behavior was over 9% different between the two, and it was obvious that someone hand ground each one. This is likely a calibration process.

View attachment 271679

As an experiment I filed down the pin in increments, until it was in its fully out position at ambient temperature. Under none of those circumstances did the clutch lock. Instead, under all situations I can test, it would run at around 980RPM at idle. Even when totally ambient, and at cold start. This was the same behavior of the other clutch as well.

This makes sense, as with my working factory clutch, my AC evap fan would come on almost immediately when idling in hot weather unless the main fan was locked, as in the unlocked position it doesn't move much air. With the aftermarket fan clutches, it rarely comes on in temps under 95F, as the clutch is always partially locked, but never fully locked.

Here is my hypothesis, I can conclude that these clutches are faulty. They are not capable of locking fully, and slip excessively in the locked position. The factory techs are getting around this issue by filing down the pins during the calibration process, so that the clutches are always in the locked position, which allows them to pass the bench test, as the test is not long enough to identify a partially locked clutch.

I suspect there is an internal fault in the rotor fins, or the fluid quantity or viscosity is insufficient to produce enough torque to drive the fan at ~80% of shaft speed.

Well, when I filed my pin down 0.005", it did cause the fan to come on a little earlier. Has to be really hot conditions, of course.

I had also drained a little old fluid from the clutch and it was grey, from fine aluminum particles, or it was grey fluid to start with. It quessed the fluid was about 10,000 cst centistokes density, as this is what seems to be put in other kinds of vehicles, so I put some new 10,000 clear cst silicone fluid in the clutch that I bought from Ebay. And used a syringe to inject the fluid... which takes patience and constant pressure, and the fluid is very dense, lol. As the clutch operation can only be tested in really hot conditions,

I am pretty sure from my first test last summer that I need to file the pin down a little more, to open the valve sooner, so I may file it down about 0.003" more....and my initial guess is that I need to drain the fluid and put in heavier density 12,000 cst silicone fluid. Also sold on Ebay. Normally there are only two variables in these clutches... the valve opening temperature and the density of the silicone oil. Any other factor would be some kind on manufacturing variance or manufacturing problem, or a plugged valve... some kind of mechanical defect.

The reason for the tiny filing amounts is that the pin presses on a lever that probably has a about a 3:1 lever ratio inside... meaning that a 0.005" pin filing results in a 0.015" valve opening distance. I really don't know the exact lever ratio, but if someone could cut a clutch open, this could be confirmed, lol!

In theory, one should be able to tune an OEM clutch to perform exactly like they want, by filing the pin and changing the fluid density. Unless the valve or return ports are plugged. Or some crazy manufacturing defect. I also pretty sure one can overfill the reservoir, but I do not know the exact fill level amount... if someone had a new clutch... they could remove the pin, then rotate the clutch in increments and see when the fluid starts to ooze out the pin hole. This would confirm the correct fill level. If I ever get my OEM clutch dialed in, I will write a report. But I normally I only get out to the desert where it is really hot about once a year.