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Fan Clutch - Severe vs Heavy Duty

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ckuske

Fan Clutch - Severe vs Heavy Duty

Administrator

I'll start by saying this... I know better now.

I bought and installed a Severe Duty Fan Clutch (Four Seasons 36704) for my truck when it was running hot when I first bought it back. I've barely driven it since then, but hope to ramp up.

When I got my A/C done yesterday, the guy said "your fan clutch acts weird, it never really kicks in". I told him that I had noted the same thing, but didn't really have anything to compare it to.

The behavior is this: When started cold, the clutch is engaged. There is lots of airflow. After about 60 seconds, the clutch disengages. The issue is even when the truck is fully warmed, it never really seems to meaningfully re-engage. This is only at ~70F ambient, so that may be the issue. The clutch isn't shot, I can barely move the blades more than a few inches when everything is cold.

The fan clutch currently installed is is a severe duty model... at the time I assumed "severe is better than heavy, so why not?". I was naive, didn't know to check part numbers, the MPC, etc. Now going to Rockauto, the Heavy Duty has a match to the part number in the MPC.

Am I correct that having the severe duty clutch installed sets a higher threshold to lock up maybe? I read that a severe duty will lock up harder than a standard or heavy, but it didn't mention the threshold to lock up, only the amount of clutch lockup once it is engaged. (https://www.rockauto.com/genImages/93/4s410-fan-clutches-standard-heavy-severe.pdf)

This seems to be a better fit (https://www.rockauto.com/en/moreinfo.php?pk=815302&cc=1121443&pt=6812&jsn=1735), but I want to make sure I can expect different behavior.

The other option is that I just haven't driven it in hot enough weather yet? But, I want cool air to be pulled in to help cool the A/C condenser.

Thoughts?

Chris

'84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread

Gary Lewis

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

I don't know what fan clutch is on Big Blue. But I do know that when the engine is started at cold temps the fan does what yours does - engages for maybe a minute. Then it disengages and doesn't come back in unless the coolant temp gets pretty warm. But I don't know what "pretty warm" really is.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

ckuske

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

Glad to hear you see the same behavior!

Since there is no feedback from the coolant temp sensor to the fan clutch, the fan clutch must be engaged by the ambient temperature inside the engine compartment, correct?

I'm sure outside ambient temp factors in as well. It's supposed to be warmer here this weekend, perhaps I'll see different behavior.

Chris

'84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread

Gary Lewis

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

It is the air temp that is passing the clutch, so is surely influenced by ambient temp as well as the coolant temp. Maybe you'll see it work this weekend.

Gary, AKA "Gary fellow": Profile

grumpin

Re: Fan Clutch - Severe vs Heavy Duty

In reply to this post by ckuske

The 86 I used to own did the same thing and had to be pretty warm out for the engine to get warm enough to engage it.

Dane
1986 F250HD SC XLT Lariat 4x4 460 C6-Sold
1992 Bronco XLT 4x4 351W E4OD
1998 GMC Sierra SLE K1500 350 4L60E
Arizona

mat in tn

Re: Fan Clutch - Severe vs Heavy Duty

the temp that the coil on the fan clutch reads is the issue. in normal operation it is reading ambient air and a bit of heat from the condenser. it really only senses a large volume of heat when the t stat opens and fills the radiator with hot coolant, that's when the surge should happen. and the clutch start driving the fan more forcefully. it is a bit of a delayed reaction being that the coil must absorb enough heat to adjust the valving of the fan clutch. this is why modern cars like the dodge ram use a separate electric fan for the condenser exclusively. adding a pusher fan controlled by a relay off the compressor will be the best a/c performance without loading up the engine with a heavy fan. I am using both versions at this time and the electrics are doing well.

ckuske

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

I'll let it be for now and see how it behaves as it warms up. I just wanted to verify this sort of behavior is typical. Thanks all!

Chris

'84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread

85lebaront2

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

On Darth, the original fan clutch would be on at a cold start then drop out, AC on in summer would bring it on, heavy traffic, slow moving in the summer with AC on and hauling a 30 ft 5th wheel. Leaving a stoplight would give me a roar like one of NASA Langley's wind tunnels up to around 40-45 mph, at which point it would start tapering off.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

ckuske

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

I got it hot enough today. It definitely works!

The wind really kicked up with very hot air, and the temp gauge dropped a little bit after that...

Chris

'84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread

ArdWrknTrk

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

That's really good to hear, Chris!

I too have a Four Seasons severe duty fan clutch.
It seems to work well IME.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

Yes, that IS good news. Does it sound like a jet plane taking off?

Gary, AKA "Gary fellow": Profile

351FUN

Re: Fan Clutch - Severe vs Heavy Duty

In reply to this post by ckuske

According to Hayden, this is the difference in clutch types

• Standard Duty Thermal: Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch (1-1/2" of pitch). Flat plate impeller design with 30 sq. in. of working surface.

• Heavy-Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans (2 1/2" of pitch). Land and groove design with 47 sq. in. of working area allows higher operating RPM's.

• Severe Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2- 1/2" of pitch). Land and groove design with 65 sq. in. of working area. Larger working surface provides cooler running and longer life expectancy.

Gary Lewis

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

Good info. Thanks!

Gary, AKA "Gary fellow": Profile

81-F150-Explorer

Re: Fan Clutch - Severe vs Heavy Duty

In reply to this post by 351FUN

Our trucks also have a centrifugal fan clutch VS. thermal fan clutches. Centrifugal Fan Clutches do not have the coil spring on the front.

Usually used with non-A/C systems. Centrifugal Fan Clutches never fully engage or disengage and are dependent with shaft speed on how fast they turn.

Truck: 1981 F-150 Explorer / Engine: 300-6 California MCU Feedback System / Trans: T-18 - 4 speed / 2.75 Ford Rear Axle Open Diff.

ckuske

Re: Fan Clutch - Severe vs Heavy Duty

Administrator

That is good to know! I had no idea when I bought it, I was learning about working on this truck in general. I just thought "Severe Duty" must be better, right?!

That being said, my truck is staying nice and cool even with the warmer temps and my A/C running, so I'm a happy camper. Now that it is warmer out, the fan is engaged more often.

And yes, it does sound like a jet or wind tunnel when engaged! It's still not louder than my C2 pump though.

Chris

'84 F-150 XL 2WD Flareside, 302 w/ AOD transmission, Motorcraft 2150 feedback carb w/ CA Emissions, EEC-IV w/TFI, factory A/C, speed control - Info about me and my truck - My project thread

351FUN

Re: Fan Clutch - Severe vs Heavy Duty

In reply to this post by 81-F150-Explorer

Interesting, I'd never noticed they weren't thermal. Our clutch has the same fan mounting as GM, so I'll probably try the 11 blade fan soon to replace that flex fan garbage I have now.

81-F150-Explorer

Re: Fan Clutch - Severe vs Heavy Duty

With the 300-6:

with standard cooling, you got the small radiator, a fan guard, and a flex fan directly bolted up to the water pump using a fan spacer adapter.

with super cooling without a/c, you got the larger radiator, a fan shroud, a solid fan, and a centrifugal fan clutch bolted up to the water pump with 4-Bolts (Trucks built before 1983). Some of the bolts are left handed threaded too. (Righty-loosey Lefty tighty)

Best pictures I have of my setup. 300/6, Super Cooling, Without A/C.

With super cooling with a/c you got a thermal fan clutch. The one with the temp spring on the front.

I highly recommend swapping the supercooling components if your trucks only have the standard cooling system. They really were inadequate when new. In my opinion. I'm going to replace the centrifugal clutch on my 300/6 to the thermal clutch if my centrifugal clutch goes bad.

Truck: 1981 F-150 Explorer / Engine: 300-6 California MCU Feedback System / Trans: T-18 - 4 speed / 2.75 Ford Rear Axle Open Diff.