[bikestuff]

Gurus,

On the way home from the rally I noticed that my engine was running a few degrees warmer than usual.  When I got home, I remembered to look at the radiator fan.  It was not spinning.  Hmmm.  I called a fellow guru and he suggested that I unplug the relay for the hydraulic fan.  (Located near radiator fan on bottom left looking towards the front of coach).  

Today, when I did that test with engine running, the fan went from not turning at all to turning at full speed.  Plugging the relay back turned the radiator fan off.

I then tested my dash AC that got fixed at the rally.  Now my radiator fan ran at about half speed.  

So far so good, but then something weird happened.

I turned the dash AC off, and expected the fan to turn off again.  But it continued to run at the slow speed.  Engine coolant temperature was not yet even warm (125F).

I turned the engine off, and then restarted.  Now the fan turns at the slow speed.

Questions:  Should it concern me that sometimes my radiator fan runs slowly and other times it does not run at all?  Could this be a sign of a radiator hydraulic motor getting ready to fail?  

Apparently the radiator fan motor has multiple speeds....what controls the speed?  Clearly if I unplug the relay, it goes to full speed, but what tells it to run a slow speed?

Cheers,
bill

[bikestuff]

Alright, I heard from a master guru and want to add to the thread.

1. In most cases we have two speed fan motors. Those speeds are 1) fast and 2) slow & off. Since we are talking about a hydraulic motor, we have to think about the viscosity of the oil. So...when the oil is cold, the motor may not turn at all...as the oil heats up the fan will start turning slowly.

2) The AC compressor idea was probably a red herring and was just coincidence.

So....Lesson Learned: The radiator fan is controlled by a hydraulic motor that has two speeds. It normally runs at the slow / off speed until the engine tells it to turn to the high speed. Once it does its thing and cools off the engine, it returns to the slow / off speed. This model matches up with everything I experienced (except for the fan not running after driving on hot day). The system is incredibly simple.

[folivier]

Just to add a bit of nothing to this I think some of the Wanderlodge guys have added an override switch so they can turn the fan to high whenever they want.

[qcj]

Bill, I can remember a time I was standing behind the coach and the motor hood open and motor running and the fan was not turning. All of a sudden it came on and blew my had off. Also going down the road the temp. would go up to above 200, the fan would come on the down to temp. went to about 185 and the fan would cut off and the temp. would come up again slowly. This would save fuel because I understand it takes a good bit of HP to run the fan.

[bikestuff]

Forest, I have also heard about that and have considered it for my coach....but would this be more than a toy? If you manage engine RPMS and keep your radiator clean, then shouldn't the system just take care of itself? In other words, when would you turn the fan on high?

Thanks to Richard, I understand the cooling system much better. (After having the coach 7 years its about time that I learned some stuff).

[Chester Stone]

In a long downhill run, such as the 40 miles between Reno and Sacramento, the engine is basically idle but the transmission overheats due to the constant use of the Jake Brake, like 250 degrees. That is when it would be useful to have a switch to bypass the fan thermostat and cause the fan to cool the transmission.

[77newell]

On a long downhill run it would be important to ensure the transmission stays in converter lockup mode to minimize heat generation. The hydrodynamics in the converter are only useful when the engine is driving the transmission, not the other way around.

[TGDianics]

Why does the transmission over heat with the use of the Jake Brake?

[77newell]

The only way I could conjure is is the converter is active, as I described above, otherwise heat generation in the transmission will be no greater than it would be under power going up a hill of similar slope to the one being descended.

However, there is one other way it could potentially happen. If, as Chester suggests, the engine is coasting in no fuel condition it will generate little heat from combustion, but there will be heat from repetitive compressing of air in the cylinders from the Jake activity. All that heat, approximately equal to the heating of the brakes if they were used instead, has only one place to go, out the radiator via the coolant. That could mean the coolant could get hot and the trans temp would rise. But, if it did that the fan should kick in due to the controller reading a high temp in the coolant. I think I just talked myself out of this one.

2nd however, if the trans is equipped with a retarder then a long descent would produce a hot trans. I couldn't talk myself out of that one because the heat is being generated in the trans itself.

[Richard]

Google how does Allison retarder work. Too much for me to type on my phone