I really don't believe that the engine driven cooling fan can help cool the works with 70 mph of ram air coming through already, and maybe I am wrong. Great to have at stoplights, but wonder if it should be inhibited at, let's say, 50 MPH. Irritating loud.


Can this fan be electrically inhibited with a speed switch of some type, or is it autonomous? It must be actuated with some heat sensor. Defeat the heat sensor at speed?


I know this seems nuts, but if you don't live in the dessert, you don't know what I mean. Losing 20 HP at highway speeds, could be argued, to hinder cooling, engine has to work harder to turn blades that may not be contributing to the cooling effort. It could be the engineers didn't make the thing very smart, and speed dependent.


A lot of speculation here, can anyone clear it up?

It takes almost as much HP to make the electricity to run an electric fan.


Fan has a Viscous Clutch, that Limit it's RPM, Temp Sensitive fluid to couple/uncouple fan.

I didn't ask about replacing with an electric????


But if I understand how it works, there is no way to inhibit the fan at high speeds, correct?


With a new clutch, is it possible to engage the fan by taking your foot off the gas in warm conditions? I may have been inducing the fan on with my loading/unloading the truck.

No way to disable it as it is not electric.


However, GM's fan clutch system is pretty much tried and true and works great on the Dmax application.


Other than scaring the crap out of you when you hear it for the first time.

How about additional cooling then? Seriously, with 110 deg daily, my ambient condtions are 40F higher than you all, I don't want to listen to this thing drag racing all the time. I'd like to hear my wife nag once in a while.


I could use synthetic oil, but it's too soon for that. Maybe I'll try to fabricate a scoop that sends more air to the middle of the radiator where the fan thermostat is located.

The Fan Clutch Fluid is a silcone based liquid that is temperature sensitive. There are different temp range fan clutches out there, not sure if any are available for the D'Max.


My Gas motor truck always ran so hot, the roar of the fan was welcome. Sort of a reassuring Roar! Let me know things were work'in!!

It's the temperature of the air surrounding the fan clutch that sets it off. If you are having air temps of triple digit, you're gonna hear the fan, no matter how much air you move. It's the ambient temp of the air that's the key.

After looking at the fan, i see the thermostat (intentionally) faces the radiator, and takes it's cues from it. If more air could be channelled there, less fan at 70 mph. How's my logic?


It still may be a poor idea, but that GMC logo sit right therehttp://www.dieselplace.com/forum/smileys/Angry.gif

also noticed the trans cooler sit in front of the radiator, centered on the thermostat, which is in front of the condenser, 3 layers of heat stacked in front of the thermostat by design. Bet that fred scoop would help.

They stack them there to make the fan work! They want the coolers to cool, and they do that when air moves accross them. The fan does that.


It's not the volume of air, it's the temperature of the air that matters.

Yup, they just should have made a quieter fan, hired cessna or something. It works.





Is that a 2 stage radiator?

Not sure what you mean by 2 stage radiator?


http://www.dieselplace.com/forum/smileys/Confused.gif

The radiator has 2 radiators, one in front of the other, closest to the fan. Then the condenser then the tranny cooler. Is that incorrect?

From the engine to the grill it goes radiator, intercooler, condenser, tranny cooler.

Thanks for clearing THAT up.. Did not know an intercooler could be so big. Have one on my 300ZX TT, much smaller, but 2x thickness. COOL

I think an electic unit would also be a better choice. While it's operating, the electric would draw similar HP as the fan-clutch, the electric could be set to operate off coolant temp. I too don't see a huge need for the fan-clutch to engage at freeway speeds, especially when the engine and tranny are already running cool enough.


Maybe a ram air system might keep the engine compartment cooler and keep the fan-clutch from engaging.


If the stock fan really does take 20 HP to turn, that does what, doubles the HP required to cruise on level ground at highway speed? Maybe it's only half-again as much, but regardless, it is a significant percentage and must negatively affect mileage.

"Maybe a ram air system might keep the engine compartment cooler and keep the fan-clutch from engaging."


I'm not a big fan of electric fans, just wish it were possible to inhibit this one electrically with some speed switch. The nose of this beast is a massive heat exchanger, stacked 4 deep. That fan is beautiful around town, and our roads can be 125-135 F.


Wonder if the engine comp dumps air effectively, if not that's where I'd go next, venturi ventilation maybe.

Why not ask the Tech Types just what the Temp Range of the Stock Fan Clutch is? Also, the clutch limits the top speed of the fan to a certain Rpm Range as well. Could be with the lower overall RPM's of the diesel, it doesn't Top Out like a Gas Motor, turning higher RPM's would.

"Also, the clutch limits the top speed of the fan to a certain Rpm Range as well."





can you elaborate? mine was spinning hard at 2400 RPM. You saying that some clutches will not engage at higher RPM.


That is why I wonder if I was inducing the fan on when taking my foot off the gas on the highway.

Clutch allows fan to spin only so fast, no matter the engine rpm.


You know, I've spent 2 days on this with you.


You need to understand the fact that when it's hot, your fan will engage, it will be noisy, and the faster the engine turns, the noisier it will get. You are driving a Heavy Duty truck. They do these things, it keeps them from wearing out like 1/2 ton sh*t boxes. Lot's of thought by folks who have read many more books on the subject than I ever will went into the design of this. Personally, I wouldn't mess with it.

Personally, I wouldn't mess with it.








No doubt good advice!

Silveradogs,
are you sure the fluid clutch is not locking the fan solid to the pulley where it sits on when fully engaged?
The fan has to move a huge amount of air to allow for sufficient cooling of engine, tranny... and since the rpm on the diesel is rather low the blade has a high pitch to much enough air, therefore its noisy when engaged. This design is VERY RELIABLE since the clutch will be only locking the fan all the time if broken and cooling is guaranteed under all circumstances. Any electric fan is much more unreliable but might move the same amount of air with less hp loss (2 fans are needed for that).
Bottomline is: The fluid clutch is temp sensitive via the silicone bath, if not needed the fan will spin loose at much lower speeds but when it gets hot it will lock and do what its designed for - move lots of air! I have not seen any electric fan out there for the duramax, only for the gassers, probably they dont move enough air....