This fan clutch is the one that the Mercedes use on there 1ton vans.
It is signaled from the box that was designed by Johnny Bridges to operate
from the temp switch as well as a manual switch.
So the fan clutch is rather simple as there is not heat strip or coil.
I have worked on several projects with Tom Prior and I hit him with hard
questions. I'm not committing to a product that does not work.
> Jim, I'm not sure I get what the problem was. By "stabilize," I am reading
> "stay within the acceptable range" and not "stay at a single temperature no
> matter what happens." The thermostat on the fan clutch is mechanical--it
> uses a bimetallic strip to engage and disengage the fluid-damped clutch.
> That thermostat is controlled by the air temperature in front of the
> thermostat. The thermostat on the engine is controlled by the coolant being
> pushed into the engine by the water pump.
>
> My severe-duty clutch is supposed to "come on" when the air temperature is
> around 210 degrees. As you point, that varies a lot from one clutch to the
> next. But, for me, the fan may come on over a range of engine coolant
> temps. The engine thermostat opens when the water temperature exceeds 195
> degrees (when using the stock 'stat) or 180 degrees, using the 'stat many
> of us use (including me). And, of course, neither thermostat is a
> switch--it starts to ease open a some temperature, and becomes fully open
> at a different temperature. The second temperature in the open or close
> action may vary based on the relationship between the conditions causing
> the temperature change (such as the steepness of the climb) and the damping
> within the thermostat.
>
> It is quite likely that these will chase each other to some extent. The air
> temperature in front of the clutch is subject to a variety of influences,
> but when traveling at speed, we would think it would be lower than the
> radiator temperature (which should be close to the coolant temperature).
> That's only true if the engine compartment scavenges air out of the shroud
> area effectively, which it doesn't when the fan is freewheeling. The heat
> bubble from the engine may extend into that zone. When it does, the fan
> clutch will engage more readily. I know this happens, because my clutch
> engages from time to time even when the coolant temperature is steady below
> 190 degrees. Something is pushing that clutch thermostat up enough to get
> it to engage from time to time. It's not my air conditioner, which right
> now is not capable of moving heat anywhere. It happens more in traffic. Of
> course, the transmission and engine oil also heat the radiator, but the
> temperature gauge is measuring the cumulative effect of that addition, plus
> the cooling effect of the radiator. (My gauge is a mechanical Autometer
> gauge, so I don't depend on an electronic sensor).
>
> When the clutch engages, the coolant temperature drops like a stone, from
> 195-200 down to 178 or 180--by "like I stone", I mean within 15-30 seconds.
> That's with a factory fan and severe-duty clutch. I conclude that when
> driven, the factory fan is exceptionally effective.
>
> So, the result is an oscillation between the lower control, which is the
> engine thermostat, and the upper control, which is the fan clutch
> thermostat. I expect there are times when they are reversed, and the
> natural damping of the thermostats allows that to resolve itself. Some may
> interpret that as "unstable".
>
> The one element in what you did to Jerry's coach that I have no experience
> with is the water pump. But the aluminum radiator is bigger and more
> efficient, which means it will dump hot air on that fan clutch thermostat
> more quickly than the stock radiator. That might make the oscillation
> worse, so that the fan comes on more readily, but turns off more readily,
> too, with less damping just from the time it takes to change the
> temperature of the coolant..
>
> A fan clutch switched on the basis of engine coolant temperature should
> reduce that oscillation, simply because the fan will now be reacting to the
> same thing the engine thermostat is: The coolant temperature.
>
> The oscillation used to bother me, because it would often happen at speed.
> I would have thought ram air would be enough to cool the radiator. But
> no...even at 60 mph cresting a long hill, the fan will come on and the
> coolant temperature will drop like a stone from 195-200 down to the 180
> setting of the engine thermostat. The fan is therefore MUCH more effective
> than ram air. But then I decided the system was working.
>
> The stamped metal fan is effective but it is not efficient--it moves a lot
> of air, but at the expensive of a lot of wasted energy--wasted on robbed
> horsepower and on noise. That's where an engineered plastic fan should be
> able to do better.
>
> Rick "thinking fan clutches have caused about as much discussion on GMCnet
> as tires and combiners" Denney
>
>
>
> > I guess I am feeling a bit "snake bit" when it comes to new innovations
> in
> > fan and "high flow?" Aluminum water pumps. When I replaced the engine in
> > Jerry Work's Clasco coach, we put in a new aluminum radiator, new 10
> blade
> > plastic fan and clutch, 2 piece shroud, aluminum water pump, the whole
> > enchilada. It would not stabilize coolant temps. I finally wound up
> doing
> > a 100 mile service call to re-install the original style water pump and
> > steel stock fan, along with a new thermostat. That fixed the temp cycling
> > problem. I am a bit leary of going through those motions again with "new
> > and improved parts". But, that does not mean that the cooling system does
> > not need improvement, it does.
> > Jim Hupy
> >
> > On Jun 26, 2017 8:21 AM, "Johnny Bridges via Gmclist" <
> >
> > > Relative to Hupy's comments, the new setup uses coolant temperature to
> > > turn the clutch on or off. The temp sensor is a lot more accurate than
> > the
> > > temperature of the air going across the clutch. The fluid sees only
> one
> > > seal instead of two, and the design and materials of that seal are 40
> > years
> > > newer than the original. Consequently we feel it will work better and
> > > last longer.
> > >
> > > --johnny
> > > --
> > > 76 26' Eleganza(?) with beaucoup mods and add - ons.
> > > Braselton, Ga.
> > > "I forgive them all, save those who hurt the dogs. They must answer to
> > me
> > > in hell" - ol Andy, paraphrased
> > >
> > >
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>
>
> --
> '73 X-Glacier 230 "Jaws"
> Northern Virginia
> Offlist email: rick at rickdenney dot com
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--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
