Electric fan musings

Now that I've resolved the Saab burned valve issue, I can turn my attention to getting my 2002 out of the garage and on the road. As usual, the winter left me with time to think about things I want to change. One of those is the radiator fan - I want to go from the  (non-clutched) mechanical fan to an electric. This was inspired by the episode of Engine Masters that tested power losses from various types of fans; needless to say, the electric was the winner by a wide margin, especially at higher RPM. Since the 2002 is a 4-speed and makes its power above 4k RPM, I'm sure the fan is costing me precious horses.

What does the hive like for this sort of thing? Do I just grab something cheapish off of Amazon and call it done? Is there some particular brand that's more reliable but won't break the bank?  I'll wire in a relay and a sensor (there's already a bung in the radiator, which is from an E21 320i), and maybe a manual override switch, so I just need to figure out what what fan to use. The mechanical fan is 360mm (just over 14") diameter IIRC, so I'm guessing I should be looking in that range for an electric. It's easier to mount as a puller, but are there advantages to setting it up as a pusher?

In reply to 02Pilot :

Any reason why you don't want to go with a preassembled kit? Ireland Engineering has a 14" kit and it's pretty reasonable.

https://www.iemotorsport.com/product/electric-fan-kit-w-fan-12-14/

In reply to MTechnically (Forum Supporter) :

I've already got the sensor, relay, and wiring, so it would be redundant. That and the fan looks to be identical to the ones that are ~$30 on Amazon. I don't mind paying for a kit when it saves me time and/or effort, but in this case I don't think it does.

Puller is more efficient/effective (especially with a shroud) by a good margin.

I've used Spal fans for a long time and never had a failure (and this is on a rally car where the fan sees plenty of mud, rocks, dirt, ice, whatever).  The rally car (due to engine swap not leaving much room for fan) now has a pusher fan (flex-a-lite Syclone) which has done well also. 

All my cars with electric fans have them thermostatically-switched and ALSO an override switch (that one time the thermoswitch failed and I didn't know....)

In reply to irish44j (Forum Supporter) :

Yeah, I want an override switch just in case. Not sure about building a shroud, but I am working on some ducting in front of the radiator, and this car has never had a problem with engine heat due to the E21 radiator and a well-maintained cooling system - I think a 14" fan by itself should be sufficient.

Honestly the biggest difference I have seen is how the fan is mounted. Straight to the radiator is marginal and depends on the overall capacity of the system. A proper shroud to activate the WHOLE radiator surface makes an exponential difference. If you can fab your own it opens up a lot of options. If you can’t, get a fan and shroud combo. I technically can, but found a derale kit that did it chePer than I could and have been happy with the results

My opinion:

I dislike the sound of aftermarket/slim line fans. They have a howl that gets on my nerves. If I have room I will try to adapt either the 2 speed late 80's VW golf fan or a mid 90's civic single speed unit. They also move considerably more CFM than a spal or Flex-a-lite.  

But sometimes space constraints require a slim fan. The Napa I use carries flex-a-lite, I have also used Spal and no name Amazon/ebay cheapies. They all seem to function about the same so I don't actually have a preference. 

A good shroud will increase the efficiency a large amount. 

But if you can zip a fan right to the core and stay cool in traffic in the summer then sweet! That is the easy button

Do you have room for the E36 fan from the 4 cylinder cars? The 318ti I had used a wonderful electric puller fan instead of a mechanical like the I6

Spal was the name when I was in the BMW world. I put one in my E36 and it was.... okay. I mounted it on the radiator and left the stock shroud. Wired it to the temp switch in the radiator and added a manual switch. I was never really happy with the setup. With my admittedly bad configuration it never was as effective as the mechanical fan. Stopped in a drive through on a hot day it would start heating up. There might have been a problem with the car too, I was done with it and got rid of it before I could find out the root problem. 

I also highly recommend a manual switch. I used it more often than not. 

If the thermo switch is working right and the fan has enough capacity to actually cool the engine, an override shouldn't be needed... Most factory aux cooling fan switches have a temperature that is too high to work effectively as the primary fan, so in some cases it might be a case of the wrong switch.

Two speed fans are definitely the way to go. On my E30, I use a Volvo 740 fan bolted to a custom shroud; it's quite quiet on low and moves a lot of air.

Fan shroud also makes a massive difference in flow through the radiator. Pullers are more effective than pushers. Use the biggest fan you can - they achieve higher tip speed at lower RPM and are generally quieter, move a significantly more air, and have better capability vs. radiator core restriction.

Published airflow numbers, especially for cheap fans, can be pretty misleading because testing may not be done for equal pressure drop/restriction.

Electric fans rarely have the airflow of a good engine driven fan, so challenging applications with limited ram air (towing in particular) may be better off keeping the mechanical fan.

Use the fan with the biggest motor and highest draw you can. That means you have the torque needed to pull air through your heat exchangers. Mount to a fully sealed shroud that is at least an inch away from the core. Add bypass flaps. 
 

A "slimline" fan on a close shroud is basically useless. 
 

I have heard the Taurus fans are a good junkyard source. 

In reply to Keith Tanner :

+1 for Taurus fans. 

Due to packaging issues i needed to install a pusher on my datsun.  I picked a Spal fan, largest diameter i could fit, and its loud... but effective.   

Being an older car, the dimensions of the radiator are quite a bit different than most newer stuff, and all the junkyards around here disappeared decades ago, so there's not much chance to go wandering about looking for something that will fit. New OE fans seem quite pricey, more than I plan to spend on this, and I'm not sure what I would be able to squeeze in there in any case. I think what I'll have to do is measure the space carefully, get the biggest generic slimline I can fit, and build a good shroud for it. If it doesn't work I'll just have to go back to stock.

One option I would consider if it weren't for the price would be the clutch fan from the early E30 318i, which should be a bolt-on setup, but at $250+ for the water pump, clutch, fan, and shroud it's not falling into the cheap upgrade category.

On my m50 swapped e30 I ran a parts store Hayden fan as a pusher for awhile until the fan motor seized up. Luckily the car was idling in the driveway when I realized it. I swapped it out for flex-a-lite and it seems to work well. It's just on a low temp factory style switch/relay with no backup override. I'm running no shroud with it attached directly to the radiator with those through core zipties and I'm amazed at how much air it moves and how fast it will cool off the core. I can't even imagine how much more efficient it would be as a puller and correctly designed shroud.

I went thru this exercise on my V8 Cougar a couple of summers back when I revised the cooling system starting with a new larger AL radiator and wanted to swap to electric fan/s.  The single mechanical 5 blade OEM fan w/o thermal clutch couldn’t provide enough airflow to keep the car cool when it was not moving.   A single 16” electric fan required a shallow shroud to clear the water pump so I ended up with an aftermarket dual 11” fan with thicker shroud which keeps car cool in all conditions.  Something to consider when changing to electric fan is the amp draw and your alternator capacity 

I’ve seen many people using Contour/Mystique dual fan and shroud combo when depth  is a concern and Taurus and Mark VIII big single fans when depth isn’t a concern.  Generally these were purchased as new OEM style replacement not used fans.  Vintage Mustang guys who prefer to not change to electric fans recommend the big block variant mechanical fans with new thermal clutches.  

Looking at some of the OE-type fan-and-shroud assemblies that are out there (the Taurus unit may be too large to fit), there are some that look plausible (a couple of Honda units in particular), but I can't find dimensions listed anywhere. Most frustrating.

As far as the amp load, I've got an 80 amp alternator in there, which I think should be sufficient, as there aren't too many other things that require significant power on the car - I can shut down my auxiliary lights if needed.

Capitalize on someone else's R&D.  Taurus fans are great if you can engineer some way to make sure they pull through the core well.

The problem with some fans is in the engineering.  Take this one for example:

This is the ever-popular Flex-a-Lite Black Magic fan.  It pulls a bazillion CFM, and it is awful in most applications.  This was designed to cool up to 500 hp, but you have to think of the application.  It was designed for hot rods, buckets, and other eye candy that only ever cruises from the trailer to the show, or the occassional parade.  It needs the fan to do all the work, so it's all blade.  Put one of these in a 200-hp malaise-era Buick, and chances are it will overheat on the highway because (although it flows impressively) it also blocks a LOT of natural air flow.  The entire cooling system in that Buick was engineered around the fact that it gets a bazillion CFM of its own from driving at 60mph.  If you restrict that flow with something like the fan above, you may need to re-engineer something else in the system.

There is a lot more to an electric fan than just how many CFMs it flows under it's own power.  Just buying any old fan from Summit that says "cools up to X hp" is not the ticket.  Using someone else's R&D (like the taurus fan) is a winner.

In reply to Curtis73 (Forum Supporter) :

That's the problem - there isn't a lot of pre-existing R&D in my application. Basically, it's either stock or some sort of generic. If I could get dimensions on the Honda OE setups (or any other one, for that matter) and confirm one of them would fit, I think they'd probably work - we're only talking about a 2-liter engine that puts out maybe 150hp on a good day, with an upgraded radiator. The Taurus rig is just too large to fit, and it's probably overkill in any case.

In reply to 02Pilot :

Honest question- what's the worst that could happen from overkill tho? Those Taurus fans are like $15 at my local JY and OEM replacements are everywhere.

Use ebay, Amazon and Rock Auto and you should be able to locate dimensions.  I found them in the past when I was considering these fans for my car.  

OK, good news and bad news. The good news is I was able to find dimensions for some of these through Rock Auto (hadn't thought of checking there). Bad news is that none of them will fit. The core is 13" x 17.25", but the depth available is only about 2", so most OE stuff is out. I can either go to a pusher or two small (maybe 8") pullers. I think the latter option is probably better. I can even hook them up to different temperature switches and relays so I can have staged activation if I want to get really fancy, but I probably won't.

Strongly recommend against a pusher for the same reasons I listed above, only they'll be worse.  You're blocking flow before it can even enter the radiator.  Great for a 41 Vicky at the drive-in, bad for a DD.

I would look to whatever is similar to yours.  90s Civic comes to mind.  Small power, small radiator, small space.  I think  you have a million OEM options.  Just make a list of 4-banger economy cars: civic/accord, corolla/camry, kia or hyundai, Mazda 3... find one with a similar core size and buy the fan.  That's where you capitalize on someone else's R&D.

In reply to Curtis73 (Forum Supporter) :

If you can find me an OE puller fan setup with 2" depth, I'll be happy to buy it. Every OE thing I looked at, including 90s Civic, is 4"+.

Curtis73 (Forum Supporter) said:

Capitalize on someone else's R&D.  Taurus fans are great if you can engineer some way to make sure they pull through the core well.

The problem with some fans is in the engineering.  Take this one for example:

This is the ever-popular Flex-a-Lite Black Magic fan.  It pulls a bazillion CFM, and it is awful in most applications.  This was designed to cool up to 500 hp, but you have to think of the application.  It was designed for hot rods, buckets, and other eye candy that only ever cruises from the trailer to the show, or the occassional parade.  It needs the fan to do all the work, so it's all blade.  Put one of these in a 200-hp malaise-era Buick, and chances are it will overheat on the highway because (although it flows impressively) it also blocks a LOT of natural air flow.  The entire cooling system in that Buick was engineered around the fact that it gets a bazillion CFM of its own from driving at 60mph.  If you restrict that flow with something like the fan above, you may need to re-engineer something else in the system.

There is a lot more to an electric fan than just how many CFMs it flows under it's own power.  Just buying any old fan from Summit that says "cools up to X hp" is not the ticket.  Using someone else's R&D (like the taurus fan) is a winner.

There is a reason that the original VW rabbit had rubber covered flaps on the fan mount. When under way, the air flow through the radiator would simply lift the flaps and continue through to the engine compartment. When stopped, it would keep the fan from sucking air from the engine bay and bypassing the radiator. It was a simple and effective solution.

My Fiat 124 did not have enough room to fit the fan between the waterpump and the radiator, instead they installed an offset fan with no shrough at all. It seemed to work well too.