Easy way to tell when fan is running while driving

[Diesel_Dave]

I have a clutched fan on my truck. I believe the clutch is electrically controlled. I'm thinking I may be able to improve my FE by turning it off when it's not needed. An electricl fan is an option, however, if the clutch is electricallly controlled, I should be able to just use that to control the fan better (which should be more efficient than an electric fan). Before I do anything, however, I want the check and see how often the fan is running "unnecessarily" as it currently is.

It's a pretty quiet fan, so I can't hear it over the engine. Does anybody have any tips for a quick and dirty way to tell if the fan is running (while driving)?

[AeroModder]

You could tap into the power wire to the fan and run an LED light into the cabin.

[slowmover]

Originally Posted by Diesel_Dave

I have a clutched fan on my truck. I believe the clutch is electrically controlled. I'm thinking I may be able to improve my FE by turning it off when it's not needed. An electricl fan is an option, however, if the clutch is electricallly controlled, I should be able to just use that to control the fan better (which should be more efficient than an electric fan). Before I do anything, however, I want the check and see how often the fan is running "unnecessarily" as it currently is.

It's a pretty quiet fan, so I can't hear it over the engine. Does anybody have any tips for a quick and dirty way to tell if the fan is running (while driving)?

The clutch is electrically controlled, both on/off and in percentage of torque application, IIRC; it's sophisticated, not simple. There are some decent threads on this subject on CTD boards related to failures due to the harness being cut by said fan, when:

Deep water fording
Regular hard off-road use

as it appears the radiator moves a bit in it's mounts (shock absorbtion?) and the harness flexes and is cut by the running fan. (May also be model year dependent). This thread goes into cross-brand "fixes" and workarounds. Some interesting stuff to play with for those so inclined.

In big trucks we know that percentage of "on" time for mechanical fans is cited in the literature as detrimental to fuel economy. Some decent threads on big truck boards about this, also, including conversion to non-engine-driven fans (completely electrical) for Class 8. (Both on Truckers Report and CAD.)

There are some conversion kits now for the CTD. I'm more than a little afraid of failure of cooling fans under tow, but others are not (see here).

The SAE J2807 Towing Guideline utilizes the infamous Davis Dam grade in Arizona to determine limits. One of which is backing a trailer on a 12% incline at the GCWR. Stop and go. In summer.

Always worthy of keeping in mind, IMO, as one need not be in AZ, much less in summer temps, to overload a cooling system. Have seen PS systems fail -- in winter -- horsing a trailer around with no appreciable airflow. Trying to move a trailer around in a flood comes to mind. Etcetera.

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[Diesel_Dave]

Thanks for the info, slowmover. Here's what I'm thinking: if the fan runs eccessively as it's currently set up (which I have yet to determine), I might be able to make a kill switch for the fan. That is, make a switch so that switch off = fan off, switch on = normal fan controlled by ECM. That way, when I know I'm not going to need the fan I can just diable it with the switch, but when I think I might actually need it I'll let the ECM control it as it normally would.

The advantage here comes from the fact that I know what I'm about to do even though the ECM doesn't. It has to control the fan assuming that at the next moment, I'm about to to the worst case scenario. For example, if it's a cold morning and I know I'm going to start, go 2 mi and hit the highway I could probably turn the fan off completely to warm the engine up faster, knowing that I'm going to be plenty cool enough when I get up to highway speed. The ECM control strategy, however, has to be prepared in case I was towing a heavy load and was going to be doing slow stop & go for a long time.

From a FE standpoint a clutched mechanical fan is superior to a pure electric fan because you don't have all the losses associated with the alternater converting mechanical power to electrical power and then an electrical motor converting electrical back to mechanical. I could see why folks might want a pure electrical fan to get more power out of the engine. If that's your goal, for a short period of time you can afford to drain the battery down and the alternator doesn't need to keep up. But for FE, I'm thinking why bother spending the money on an electric fan conversion when I can get a better FE solution with just a fan kill switch.

[skyking]

Dave, in my truck it is a viscus oil clutch, not an electric. Believe me it drags all the time. with your truck you can put your hand in there when it is cold. Mine would probably slice up a ham nicely.
I'm going electric because of this. If I had your fan (and ECM, and engine) I would not change a thing. I think you are barking up the wrong tree here.
an active grill block and a way to monitor the fan would be my choice. Close off some grille but don't change the way the fan cycles.

[NeilBlanchard]

Is the engine temp getting hot enough to start the fan? My car gets up to 204F before the fan comes on. What temperature starts the fan on your truck?

[slowmover]

But for FE, I'm thinking why bother spending the money on an electric fan conversion when I can get a better FE solution with just a fan kill switch.

Dovetails with my concerns: don't make changes you may not be able to afford to fix if the truck is needed to work extra hard (even beyond GCWR spec) and money is desperately needed elsewhere.

I'm looking forward to what you find. The back & forth power conversion doesn't look worthwhile to me purely from the standpoint of complication (and being non-OEM on a $16k long-block).

Think you could post the FSM schematic for where the switch will be installed? (as is convenient) Will you also install a flashing dash light or other in the event of forgetfulness? I've run down the road for hours in a Class 8 where I had overridden the auto function and manually turned the fan on . . . just forgot to turn it back off.

NeilBlanchard, although there are several important changes between his truck and mine in just three model years, my fan starts from the moment go. I haven't run the truck in about 5-days. Temps are in the mid-80's. With no A/C or other the fan starts with the engine, but almost free-wheeling. It is also of plastic or composite construction; very light in weight.

With a hot shutdown (relatively) and A/C engaged in summer temps, the fan not only comes on, but comes on with greater percentage engagement.

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[Diesel_Dave]

Well, the first step for me is to find out whether the fan is actually running "excessivly" or not. By that I mean, is it running anytime when I wouldn't want it to be on. That goes back to my original question. Before I fiddle with anything, I want to know how much room there is for improvement. If the ECM is already doing a fairly decent job, then it's not worth messing with.

Slowmover, here's just a thought for you. Could you replace your mechanical clutch with an electrical one rather than going with a entirely electric fan? The challenge as I see it with that though would be controlling it (since your ECM isn't set up to do it). Of course you probably could do it with a manual switch all the time but that would be a pain (and a risk that you might forget it). Here's another option though: those electric fans must have some type of controller, so maybe you could use the controller from an electrical fan and put it on an electrical clutch. Just a thought. And keep in mind that electrical stuff isn't my strong suit.

[slowmover]

As above, I'm not at all inclined to mess with the factory setup. So far as I can tell it already minimizes HP loss versus the 1st/2nd Gen trucks (where going to a HORTON fan clutch was a popular mod).

I "know" I might gain 1-mpg in solo, unloaded conditions; and perfroma well even in conditions "difficult" for the drivetrain (almost all of them, including sand, mud, etc); but it is the situations of being loaded and towing, and having to traverse difficult terrain (the above; plus gravel; or hills and mountains, etc) that keep me from wanting to mess with it. Once a diesel gets too hot, it's too late. I've had overheated V8-engines that "recovered" without incident, but I doubt I'd be able to say the same for this level of compression/cylinder pressures.

That said, I don't know as much about the fan operation as I might. I asked for FSM schematic for others, not on my own behalf. I am certain this will be a popular "mechanical" mod for the CTD (versus software ops) . . just not my own, ha! I'll look into the 555 operation at some point.

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[Diesel_Dave]

Does anybody know whether a Scangauge will give you the fan speed?