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Open Roads Forum  >  Tow Vehicles

 > Loss of Power after New Fan Clutch

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beergardens

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Posted: 06/21/21 07:07am Link  |  Quote  |  Print  |  Notify Moderator

I also think that they may have replaced your standard duty clutch with a heavy duty or “trailer tow” fan clutch. It may end up being a better choice overall, but if you really can’t stand it, get an OEM one to replace it with. The dealer should be able to find out the part number of the one the truck was originally equipped with.

Cummins12V98

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Posted: 06/21/21 12:02pm Link  |  Quote  |  Print  |  Notify Moderator

ScottG wrote:

Devo the dog wrote:

Put on an electric fan.


No electric fan can move as much air as the stock clutch fan on these trucks. That's why they use them.


I agree on that if he had a Diesel. Some of the electric fans do a great job on gassers.


2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
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RoyJ

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Posted: 06/21/21 01:38pm Link  |  Quote  |  Print  |  Notify Moderator

ScottG wrote:

Devo the dog wrote:

Put on an electric fan.


No electric fan can move as much air as the stock clutch fan on these trucks. That's why they use them.


As of 2021 all domestic 1/2 tons come with OEM e-fans. The much smaller fan to shroud clearance has a decent increase in efficiency, hence Ram gets away with 900 - 1000 watts instead of the 5 - 10 hp mechanical fan.

But in the OP's case, something is not right. Even a 10 hp parasitic draw shouldn't decrease speed from 50 to 40 mph, that's closer to a 50 hp draw.

Devo the dog

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Posted: 06/21/21 01:51pm Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:

ScottG wrote:

Devo the dog wrote:

Put on an electric fan.


No electric fan can move as much air as the stock clutch fan on these trucks. That's why they use them.


As of 2021 all domestic 1/2 tons come with OEM e-fans. The much smaller fan to shroud clearance has a decent increase in efficiency, hence Ram gets away with 900 - 1000 watts instead of the 5 - 10 hp mechanical fan.

But in the OP's case, something is not right. Even a 10 hp parasitic draw shouldn't decrease speed from 50 to 40 mph, that's closer to a 50 hp draw.

Furthermore, the e-fans used on autos for the last 15-20 years typically outlast the radiators, hoses, etc.

I agree with RoyJ. Something's not right. If the fan clutch is kicking in often and you can't maintain speed, you have other problems.

ScottG

Bothell Wa.

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Posted: 06/21/21 02:07pm Link  |  Quote  |  Print  |  Notify Moderator

Cummins12V98 wrote:

ScottG wrote:

Devo the dog wrote:

Put on an electric fan.


No electric fan can move as much air as the stock clutch fan on these trucks. That's why they use them.


I agree on that if he had a Diesel. Some of the electric fans do a great job on gassers.


No difference between the two when it comes to cooling. The truck was designed with a 15~20 HP fan to move enough air. That HP is directly proportionate to air movement. The clutch doesn't take more power because it's inefficient, it needs more power because it does more work. No electric fan will move as much air and if the truck is operated near its limits, it will overheat with one. Not talking about any other truck than the OP's. If he takes off the clutch and cobs on an aftermarket unit, it will overheat at its limits.

But even newer 1/2T's have clutch fans. My neighbor has a late model F150 with HD towing pkg and it has a large clutch fan - because that's what it needs to keep temps down.

It would be a mistake to try and get rid of perceived parasitic losses at the expense of cooling power.

Also, you do not want to add an electric fan to a system that already has a clutch unit. The electric fan will block airflow and cause performance issues. Besides, pusher fans don't work nearly as well as pullers.

RoyJ

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Posted: 06/21/21 06:00pm Link  |  Quote  |  Print  |  Notify Moderator

ScottG wrote:

But even newer 1/2T's have clutch fans. My neighbor has a late model F150 with HD towing pkg and it has a large clutch fan - because that's what it needs to keep temps down.

Also, you do not want to add an electric fan to a system that already has a clutch unit. The electric fan will block airflow and cause performance issues. Besides, pusher fans don't work nearly as well as pullers.


What year is the F150? Every model I've seen (at least the EB engine) uses twin e-fans. Fuzzy photo, but you can barely make out the fans behind the rad:

[image]

Not saying that's the solution to the OP's problem, just that there shouldn't be a perceivable power loss on a modern 1/2 ton. 1 - 2 mph loss, maybe, not 10 mph.

My 2014 Ram hemi uses a shroudless e-fan in front of a mechanical fan. I've since deleted both and installed a brushless e-fan from a Pentastar. Not overheated once towing 8500 lbs, though our temp don't get that high.

The modern 1/2 ton Ram has a higher GVW with only a brushless e-fan (higher wattage than mine). And we know how strict OEM cooling certification is!

Devo the dog

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Posted: 06/21/21 06:05pm Link  |  Quote  |  Print  |  Notify Moderator

How much HP is needed to turn the fan to transfer heat at highway speeds, if the radiator, water pump, thermostat are working properly and there isn't any blockage in the cooling system (airflow or coolant)?

ScottG

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Posted: 06/21/21 07:05pm Link  |  Quote  |  Print  |  Notify Moderator

Roy, Neighbors truck is 5L. I don't think one can assume everything in back of the fan is the same though. Different engines have VERY different thermal efficiencies and thus, different cooling needs. Shape of rad probably dictates fan type and configuration too. Calculating cooling requirements is over my pay grade!

Devo, that is a complicated question. Under the conditions you state, it probably takes no power at all - fan can be disconnected. But When conditions are at their worst, like climbing mountain w/AC and heavy trailer, it takes a lot of power My truck uses up to 23 HP just to turn the fan.

My advice to the OP is to live with it for a while. Better to have ample cooling than more speed. Also, don't jump into doing some kind of modifications when what you have works.

As a side note and I don't know if this is true for 1500's, but when it comes to clutch fans for Ram/Cummins, only the OEM will do. Aftermarket clutches are notorious for having performance problems.
If the problem is really bothering you, ask if they put an OEM clutch on. They are stupid expensive but work great because Ram continues to revise them for both better cooling and AC performance. Last year I replaced mine and it works better than when it was new (but again, it's a diesel).

Devo the dog

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Posted: 06/22/21 07:34am Link  |  Quote  |  Print  |  Notify Moderator

ScottG wrote:

Devo, that is a complicated question. Under the conditions you state, it probably takes no power at all - fan can be disconnected. But When conditions are at their worst, like climbing mountain w/AC and heavy trailer, it takes a lot of power My truck uses up to 23 HP just to turn the fan.

If it's a complicated question, yet you have a solution, then it's not a complicated question.

You said it yourself: it doesn't take any HP.

If the OP is experiencing this problem a lot and "everything" was replaced, then there is a problem that still exists. I also think it's funny that coolant and oil temps aren't even mentioned.

But, we know that the fan roars and the truck is 10 mph slower. LOL. Something is wrong.

BTW, how are you measuring that it takes 23 hp to turn your fan? Dyno?

ScottG

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Posted: 06/22/21 10:48am Link  |  Quote  |  Print  |  Notify Moderator

Devo the dog wrote:

ScottG wrote:

Devo, that is a complicated question. Under the conditions you state, it probably takes no power at all - fan can be disconnected. But When conditions are at their worst, like climbing mountain w/AC and heavy trailer, it takes a lot of power My truck uses up to 23 HP just to turn the fan.

If it's a complicated question, yet you have a solution, then it's not a complicated question.

You said it yourself: it doesn't take any HP.

If the OP is experiencing this problem a lot and "everything" was replaced, then there is a problem that still exists. I also think it's funny that coolant and oil temps aren't even mentioned.

But, we know that the fan roars and the truck is 10 mph slower. LOL. Something is wrong.

BTW, how are you measuring that it takes 23 hp to turn your fan? Dyno?


I see the usual downward slope of this thread so this is my last post on the subject.

First, I said it doesn't take any power just going down the highway under light load.
Second, I don't know that I presented a solution - I simply made a suggestion. In no way am I or anyone else here qualified to redesign the OP's cooling system.
I have worked through cooling problems on vintage V8 cars though and have learned a few things. There are far more variables to it than most think.

I think the OP should use it as-is and see if his results are consistent. Indeed, it is hard to believe he lost that much speed but I won't discount his experience. OTOH, a fan roaring while it's working hard is a good thing. If it's roaring anytime he's under 10 MPH, even when the eng is at normal op temp and the AC is off means that clutch is junk.
My new OEM clutch does roar anytime I'm going that slow with the AC on - that's a positive change. Not only will the AC work better but the pressures will be lower as well, making life easier for the compressor.

The 23 HP figure is what Dodge engineering reported. This is not the power it uses just going down the road under light load. It is the amount of power it *can* use when called on.

Have a good day.

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