Flex Fan Clearance

75Bronc · May 24, 2018

I am running a 6 blade Derale Heavy duty flex fan. I have over an inch between the fan and the radiator and feel comfortable with that side of the fan. But I only have around a quarter inch between the fan and the tensioner pulley. Is there any chance the fan will flex towards the engine?

I don't want to move the fan closer to the radiator, am I safe to run this?

Thanks!

DirtDonk · May 24, 2018

With an inch, you actually have room to move the fan slightly forward I would think. But you may not need to, and can keep the whole inch because the fan flexes towards the radiator and away from the pulleys. Usually anyway.

Is this how it's been running so far, or did you just set it up?
The fan blades of a flex fan should be at their maximum rearward positioning at slow speed, and flatten out at higher rpm levels.
So I think you're safe. And may not have anything dire to hit anyway.

What kind of drive setup do you have by the way, that you have a tensioner pulley?
Got pics?

Paul

DirtDonk · May 24, 2018

Nevermind. Read your details and see a serpentine there in the list of mods. Thanks for putting that there by the way.
Sounds like a cool setup.

Paul

75Bronc · May 24, 2018

Thanks for the information Donk. This is a new setup. I was running stock front dress and 7 blade fan. Now I am running F250 front dress, I am using the engine out of the donor truck I pulled my ZF from. I didn't have clearance for the clutch fan that came with the f250 and the bronco fan wouldn't work because I needed a reverse rotation fan.

centex77 · May 24, 2018

Everything I’ve read says you need at most an inch of clearance. So if you’ve got more than an inch between the fan and radiator then I’d just get a bigger spacer. I had to get one for mine. I’m running a 1” on mine instead of the 3/4” that was on it. Spacers are $10 or so from just about anywhere.

blubuckaroo · May 24, 2018

This happened when mine had 3/4" clearance. It happened during a 5000 RPM power shift crowd pleaser.:-[
I checked the tranny and motor mounts afterwards. All were tight. That engine can move around a lot!
I found that my mounts had become squishy with age and had allowed the radiator to move back a bit. I replaced the mounts and rubbers and was able to get it back to 1" fan clearance.

75Bronc · May 24, 2018

Buckaroo, how close was it to the engine side of the fan? I am questioning if the fan can flex towards the engine at all?

Thanks!

blubuckaroo · May 24, 2018

75Bronc said:
Buckaroo, how close was it to the engine side of the fan? I am questioning if the fan can flex towards the engine at all?

Thanks!

The fan clears the lower pulley and A/C clutch by about 1/4". The fan blades actually flatten out, but I'm sure you can expect the blades to flex forward a bit when pulling air. Even more if you get into water.
In my case, I think it was more about the motor mounts flexing during the gear shift. Once the fan contacted the radiator, it got distorted and dug right in.

i

Rustytruck · May 24, 2018

The only real issue with your fan is if you decide to go swimming and decide to motorboat the fan. Make sure you have the transfercase snubber in place to help keep the engine from coming forward on its mounts. Good engine and transfer case mounts are important too.

https://bcbroncos.com/shop/drivetrain/transfer-case/22-00310-d20-snubber-for-early-ford-bronco/
https://www.wildhorses4x4.com/product/Transfer_Case_Snubber/Bronco_Dana20_Transfer_Case

75Bronc · May 24, 2018

Thanks for the information. I have a ZF5 with BC Broncos cross member/transmission mount. I don't know if I can use that snubber. I think the transmission cross member holds it in place pretty tight though.

blubuckaroo · May 24, 2018

75Bronc said:
Thanks for the information. I have a ZF5 with BC Broncos cross member/transmission mount. I don't know if I can use that snubber. I think the transmission cross member holds it in place pretty tight though.

It's worth a look.
When I had my failure, I checked the NV3550 cross member. It has no snubber, but the cross member blocks any forward movement by design.

rguest3 · May 25, 2018

75Bronc - I would ditch the flex fan.

The late F150, 250, Bronco Ford serpentine is the same depth as the original Bronco. If you still have a 3-core radiator (Stock Thickness - Toms has one for the 5.0 conversion and 3-Core), use a 1/2" spacer and a rigid 17" fan. This works great even here in Hot, Humid Florida. Slight trim to the original Fan Shroud for the tensioner and that's it. I have done this in about all my builds without any overheating issues even with a 351W.

Many go to the Thicker 4-Core radiator and then do not have enough room to put a decent fan behind it. Therefore, you will have very compromised air flow. Great disadvantage with this set-up.

Broncobowsher · May 25, 2018

The fan will never move closer to the engine. Being attached to the engine there is no issue with mounts moving or anything like that.

But the fan will move. It will flex forward. As the blades load up against the air they will pull forward, just a bit.

Flex Fan Clearance

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