The Stovebolt Site Forums The Shop Area Engine Shop Fan shroud question

How close is to close for a fan shroud? My fan is only 1" from the radiator, but it sets low in the engine bay so the top 1/3 of the radiator core has no fan pulled air. The shroud would only be 1" from the core. Will this block more air and cause a overheat on the road? The fan just doesn't pull much air, its a 17" dia. low profile on a slightly smaller then stock pulley for faster rpm.

Joe

Joe -
Why don't you let the fan shroud cover the entire back of the radiator so it can pull air through the whole radiator? A 17" fan is about as large as you can go and 1" from the radiator core is about twice as far back as the stock fan set up would be on your truck. I have actually considering the same sort of set up myself for my 37. The other thing that I have considered is getting an electric fan about 17" in diameter set up in the center (top to bottom) of the radiator with a nice fiberglass shroud.
Joe

The shroud would cover the whole radiator, just the bottom 1 1/2" would be below the core. The fan is something I pickup at a swapmeet, and just doesn't pull much air.

I was afraid the shroud would be to close and slow the air flow. I am going ahead with it, if it overheats then, off to the trash bin with it.

Joe

I added an electric fan out front at the top, makes up for my same situation with the engine fan down low. I do not have a shroud at all and this set up works fine.

Actually I do have a factory shroud off of a two ton, but again it's made to line up with the stock fan location.

How close should the fan be to the radiator? Joe, you say 1" is too far back and needs to be closer to the radiator? My fan is about 2.5 inches away from the radiator, although with a shroud

factory with the 235 is 1/2 - 3/4" max ... 55-57 with the [shorter] V8 they moved the rad back to maintain that clearance - 58/9 with the V8 they supplied a shroud

Bill

1" from the core doesn't bother me, its just a cheap fan with little blades thats causing the problem. At speed, the temp is stead as a rock, its at idle thats not cooling all that well. Even doing nothing, the truck will run all day, any day of the week, I just like to see it stay at thermostat temp and not creap up. I might look in to moving the engine/trans back just a bit (1/4") then I can put the bigger fan back on a the problem will go away.

Joe

I have had some comments on how close to the radiator the fan is, but the truth of the matter is that factory specs call for it to be 1/2" to 3/4" from the radiator. It does make a little tight to change a fan belt, but it can be done.
Mine has a 16" electric fan up high on the front outside of the radiator, also, along with the engine fan and under almost all conditions, I can keep it cool, either driving slow or at idle. I'm just always looking at a better way to do it!

The fan can be 3 feet from the radiator, if all the air from the rad goes through the shroud.

Very true if sealed up tight.

But how close to the radiator is ideal for a shroud? 1" 2" 3" ???

I'm off to the store for a sheet of aluminum or steel, depends on the thickness and price!

Joe

"sealed up tight" isn't the issue - any distance from the rad is fine for the fan, and the shroud doesn't have to close off the whole rad, but you need to have the opening that the fan sits in a fairly snug fit, with the blades centered in the hole [front to back] - like this - you just want to force the fan to pull air straight from the front

the reason your truck heats up idling is the fan is too far back, the fan is pulling air from the sides and just thrashing it about, not pulling it thru the rad - the reason the temp is OK at speed is cuz air movement takes the place of fan forced flow

here's a pic of the style I prefer [yeah, the rad needs attention ], came from some 60s/70s GM car, allows better air flow at speed and does the job perfectly idleing in summer - note the fan is 6-8" back but right at the shroud opening and the shroud is within 1/2" of the rad, per the Generals specs

Bill

While I'm sure everyone wants to retain some originality I am becoming more and more convince its OK to run an all electric fan...especially on modified like mine...V8 in an old truck. With my siutation the engine sits low anyway. I ran a flex fan and a "pusher" fan located in front of the radiator up at the top. I had a "switch" I could flip on when needed in heavy traffic but I still had some problems. So, in with the aluminum radiator, and while it is definitely better its still not quite where I want to be temp wise. SOOO, when I put the V8 in my panel my neighbor gave me a big "puller" fan that covers just about the entire radiator and it cooled his Blown 350 in his 59 pickup. I look at a LOT of cars and trucks at shows and talk to owners and how they like the electrics and I have had at least a 98% positive feedback.

So, its all electric on the PanelI'm working on and I just priced a big fan for the 37 pickup. Its not cheap, coming in at about $140 with my discount. But, I've decided its the way to go and will make the conversion on the 37 soon. It just makes good sense.

I know, each to his own, but this is just my experience/opinion.

electric would solve some problems, but I hate to hear them! I know they work good, just can't get myself to do it. I have my shroud all designed and ready to cut out. I will let you know how it does.

http://www.summitracing.com/parts/FLX-1017/?rtype=10

This is the main problem, blades to small to maove air at low idle speeds!

Kpe

Electric fans are OK, but:
1. they move less air than a good mechanical fan
2. if you have a generator, they drain the battery when idling
3. even some alternators are overloaded at idle, if the lights, stereo etc. are on
4. pusher fans are the worst - they obstruct the core
5. how do you get home when they die?
6. if they have a temperature probe but no switch, they run long after the engine shuts down, = dead battery
7. you still need the shroud to completely cover the core

The most efficient shroud shape is a funnel - the longer the better, to have a gradual taper for air to reach the blades.
The reason some fans are very close is simple: no room.

Also, don't go with 100% coolant, water cools better so minimal coolant may help.

not quite so panic, for our purposes [we're not building turbines] the reason all fans are close [or have shrouds] is so they draw air through the rad rather than from the area behind the rad - GM engineers weren't just randomly positioning things in there without good reason, you'll find every old GM vehicle has the fan spec'd within 1/2-3/4" of the rad, or they have a shroud [a fan shroud, not a rad shroud]

as I pointed out above, a shroud serves to force the fan to draw air from straight ahead, through the rad, otherwide it'll draw air from the sides, which is why the critical point is that the blades be pretty well centered in the shroud hole, not in front or behind it

a shroud need only enclose the fan blades, not the entire rad surface, and GM in fact made all shrouds that way early on when the layout resulted in the fan being further away than "dangerously close" - my 58 would have had a shroud similar to the one I scrounged from a wrecker to cure it's heating up at idle, even in cool weather it didn't do well without it, with it even the hottest summer days are not a problem

when the vehicle is at speed, air flow thru the rad happens regardless of the fan [at high speeds, in spite of it], when the fan functions is with the vehicle at rest, and under no load, it doesn't require every square inch of the rad to have air moving thru it to maintain the correct temp

Bill

Bill, that shroud would solve a lot cooling issues and wouldn't create more by blocking incoming air. I might redesign and try something like that. It should will be easer to get in place.

Joe

Joe, yes they are easier, I installed that one on mine, and the vendor one in my buddys panel truck - mine was much easier to deal with and actually works better, I suspect because the size of the sheave on his water pump isn't quite "right", whether that affects the speed of the fan or the speed of water flow .... GM really did engineer these designs

GM made shrouds that way because a full shroud at speed can impede movement-caused air flow because the fan isn't turning as fast as the air is coming thru, that's also why electric fans are thermostaticly controlled, they can freewheel when they're not powered because movement is doing the cooling

Bill

Thanks for all the ideas and suggestions, now I have to decide which way to go.

Joe

a shroud need only enclose the fan blades, not the entire rad surface, and GM in fact made all shrouds that way early on

There are 2 different terms for that.
It's called, in engineering terms, a "mistake". In accountant-speak, it's called "reduced cost".
It happens when they decide that making a single duct (i.e., a device to enhance the efficiency of a fan, rather than a shroud, which by definition restricts and focuses air-flow) to save money, and apply it to as many radiators and chassis as possible.

It works fine if the engine:
1. develops no power
2. can use a fan far too large
3. gas is 20¢ a gallon
4. has a grill opening the size of a barn

They sort of stopped making these about 40 years ago.
A full shroud (as currently found on everything) needs a smaller radiator, smaller fan, and smaller grill.

"a mistake"?? isn't engineering situation-specific and evolutionary? would the "smaller radiator, smaller fan, and smaller grill currently found on everything" work for an otherwise stock TF truck? why would you want to use a shroud that restricts air flow all of the time instead of a "duct" to enhance air flow under the conditions that's useful, without restricting it other times?

we are talking about 40+ year old vehicles [with the frontal area of a barn] and 40 year old technology and making them work dependably as designed

Bill

I can see both points, the duct will only cool whats in front of it, a shroud will cool the whole core, if the fan is capable of pulling enough air. In my case, the fan is the problem. A correctly sized fan will work with both a duct and shroud.

Joe

A simple tin shroud was enough to keep my truck from overheating when idling on a warm day with the water pump in the low position. I have since gone with the adapter plate to move the pump up higher and done away with it.

http://s176.photobucket.com/albums/w186/curt160/waterpump/?action=view&current=w.jpg

Joe, I'm not sure what is recommended or what CFM's are available in Electric fans but the biggest at the local flaps are 1500 cfms. So, what would a "correctly sized fan be"....anyone got any ideas or facts?
Has anyone info on how many CFM's a fan should pull to properly cool a 6 or 8 ?? ...speaking in "general terms" if there is such a thing!!

There I go, thinking again!

1500 cfm is enough to cool a 4cyl engine is a 200lb car, but not a v8. smallest i'd look at is 2500 cfm

Use a clutch fan! place fan half in and half out of shroud. (very, very important) The "tip flow" will be stopped if too far in and overall airflow will be greatly reduced. Too far out, you get side suction. no good either. Shroud inside diameter needs to be real close to fan outside diameter. You can be back as far as 2" from Rad. There is a dead zone in center/hub of fan, sometimes back a little will help this dead zone collect more air, But following what GM does now a days, distance wise, is a good idea. There are many reasons fans and shrouds are different on modern vehicles: inhanced cooling runners in engine, aluminum parts, cost, space, engine oil coolers, high speed water pumps and many have thermostat controlled electric fans. The full shroud did not do THAT much! For our old trucks, A GOOD MULTICORE RADIATOR and a properly located shroud is all you need. If it overheats after that, somethings wrong with pump, thermostat, timing, engine full of crud, or you live in Arizona.

No clutch fans here. I have 1 1/2" from front of pulley to radiator core. I would have a bigger fan if I had room. '37's are small and with a 250 in place of the 216, I have even less room (design flaw on my part when placing the engine and trans).

I am looking in to cutting the front sheet metal to move the radiator forward, or shorting the drive shaft and moving the engine back. Some how I have to come up with more space. The aluminum radiator has a thicker core, thats what cause all this.

As long as I don't idle through a parade, I will be fine. I was just curious about clearance and air flow threw and around a fan shroud.

Thanks for all the tips and ideas.

Joe