Fan shroud

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Apr 14, 2018 | 04:37 PM

GoldCo

Thread Starter

Laughing Gas

Joined: May 2015

Posts: 826

Likes: 21

From: Golden, CO

Fan shroud

I’ve seen shrouds cover the setback of the entire fan (from radiator back) but also have heard that the back half of the fan should not be shrouded.

Any thoughts? Got a good deal on a shroud but it will most likely need cut down, so wondering how much to shave off, thanks.

BTW, mechanical clutch fan on 351W.

Apr 14, 2018 | 05:23 PM

52 Merc

Hotshot

Joined: Oct 2009

Posts: 16,173

Likes: 4,780

From: Burbank, WA

The rule of thumb I read years ago with fan literature is the fan should be half in/half out of a shroud for proper function. In too far and the air will cavitate. Out too far and it won't pull efficiently and you end up with more of an air dam. You also, ideally, don't more than a 1/2"-3/4" gap between the blades and the shroud edge.

Apr 14, 2018 | 06:31 PM

CBeav

Elder User

Joined: Jun 2015

Posts: 791

Likes: 11

From: Louisville

It's a can of worms. A lot depends on... everything. Blade design and pitch, just a flat cut hole or more of a stator design, flex fan or rigid. Blah, blah, blah. On our fire trucks the fan is a basic design and is placed about an inch inside the shroud. The fan itself is about 4", front edge to rear edge, and has about an inch clearance between it and the shroud. They are designed to keep all of the heat under the truck (to keep water from freezing in the pump and plumbing) and still not overheat so... Meanwhile the ambulances (F-450 diesels) have a stator bolted to the engine in order to provide a very tight fan clearance and maximize cooling. Our ambulances run 24/7, only being shut off for service. It takes too long to heat or cool the interior if the engine is shut down. One thing to consider is when these trucks were built a fan shroud was uncommon and many considered them more of a safety device than a cooling enhancement so you're pretty safe with most anything, provided the rest of your system is in good shape.

Apr 14, 2018 | 10:12 PM

ranger pat

Cargo Master

Joined: Mar 2001

Posts: 2,759

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From: Elk River, MN

Some older trucks had no shroud, which is fairly dangerous if the hood is open and the engine is running. I have seen a rag picked up off the horse collar and sucked through the fan. Other trucks have only a finger guard. And that is just what the name implies, guards the fingers but does nothing to enhance air flow through the radiator. Our vintage of trucks need at least what came on them when they were new. If there are any performance mods or engine or transmission upgrades to automatic, a full shroud is required to move enough air through the radiator to insure proper cooling. the rear of the fan should stick out the back by 1/4 to 1/3 of the fan blades. Clearance from the blade tip to the shroud should be 3/4" to just less then 1". If A/C is used, every attempt to funnel air through the radiator is required, including rubber seals along top like the stock vehicles had. Placement of an a/c condenser or transmission cooler should be spaced at least 3/4" apart and 3/4" from the radiator. These guidelines, I gleaned while working several years as a Ford truck cooling
development test engineer.

Apr 15, 2018 | 09:42 AM

56panelford

FTE Legend

Joined: Oct 2005

Posts: 283,683

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From: northwestern Ontario

Well can't post a picture because the IT guys are fixing things again but I used a stock V8 fan shroud from a 56 ,split it in two halves and bolted in stock location to radiator. Have a 351 W with mechanical fan. Had to trim back the opening 1/2 ". blades show about 1/2". Have AOD transmission and running A/C with no over heating problems. Tried posting a picture but site won't let me there might be one in my build thread.