Fan ON or OFF on track?

I redesigned my cooling system for this year. 

& I've been messing around with electric fan turn on temperatures. 

I'm curious if it would be better to have my electric fan not turn on at all above certain speed like 100mph+

Some people say have the fan off. others say even with 100mph air flow to the front of the car, the fan turning on can still flow more air than having it turned off.

I'm trying to lower of engine temps on track.

Pic is my new radiator shroud and flap combo.

I've run many race cars with no fan at all.  As long as you make sure all the air that comes through the grill has to exit through the radiator you shouldn't need one.  If you ever have to sit with the car running(hard to start hot?), that is when a fan come in handy.

I don't have one on my SpecE46 right now. Running the car on an 85F day the water temp never went above 209F and oil never went above 216F. I have a fan to hang on the car but I don't see needing it while on track at all.

In reply to jgrewe :

I do a lot of Autocross & street driving along side track days. so unfortunately I have to run some sort of fan/Shroud combo. Currently hitting around 220F engine 270F Oil after a 20min secession at 85-90F ambient.

Do you know if guys Running fans still have them on at track speeds? Seems to be A lot of mixed opinions 

Not your car, but I run a Fiat X19 in Lemons, while on track/at speed fan off is fine. Slow yellow and rolling through the paddock or sitting on put lane, fan on is needed. I figure that once you're above the speed your fan normally pushes air at it's basically a wash.

You'll reach equilibrium with your thermostat either way with a properly sized rad, so the increased alternator draw for a possibly slight cooling effect isn't worth it for me

Test it and see, I can't think of any real negative's to running it at speed other than the draw on the electrical system (which will be less than at a stop with the air being forced through it). Maybe it helps, maybe it doesn't make a difference but you really wont know until you try.

I replaced the power sucking clutched mechanical fan on my E28 last year with a pair of similar spal fans mounted direct on the radiator with no extra shrouding which some would claim is not a good setup. However I have the fans on a pwm controller from a random Ford controlled by my ECU with a table based on engine temp and vehicle speed. As the temps warm up, the fans come on and continue to speed up, as vehicle speed goes up the fan speed comes down but if engine temps still rise the fans can speed up to compensate. I'm a firm believer that mechanical, clutched fans have to be able to move so much air because they are controlled so poorly, they're tied to engine speed and are slow to react to temp swings. I used to come off the track even with a cool down lap and have the car want to puke a bit coolant when I hit pit lane, now I can come straight off a hot track (or red flag) and don't have to worry as the fans are ahead of the problem keeping things where they need to be.

Road raced an E30 BMW for several years. Never had the fan turned on unless I was sitting on grid. 

I run the fan on my lemon all the time. 2.5 hour stints at full throttle and it never turns off. I doubt I need it, but it's hard to reach the switch belted in so it stays on just in case of a red flag or the like.

Only way to know is with testing. Run it both ways, and see what the temps look like. If you don't do that, you are just guessing.

I've needed to turn it on at 100mph and it made a difference.

With those temps, I would make sure the oil cooler is getting air through it. Or install one if there isn't one,lol. If you have one and it is in front of the radiator, the air could be hitting the face of it and going around instead of through. It needs to be as close to the radiator as possible or at least have a shroud that extends forward of its face to make it difficult for the air to go around.

The problem with not running the fan is that it's still blocking air flow.  So if the fan is on the car, I don't think there is any reason to turn it off.

As stated above, make sure that air is getting to the radiator with proper (sealed) ducting.  Also make sure it has a clear path OUT of the radiator.

I don't think I saw this here, but nothing is free. Even an electric fan takes power to run, and that is horsepower that you don't have pushing you down the straight. My fan runs constantly because I apparently broke something and now it's unhappy. I wish I had that 1 hp that they are zapping from me back. If you can make your fan automatic, I'd do that.

Also, I don't want to be responsible for remembering to turn them on, so if they were on a switch, they would probably just be on all the time. Better lose that 1 hp than bake the engine like a doofus because I forgot the fan.

I've found that it's more about sealing off all of the areas between the grill opening and radiator more than running a fan. If you make sure that all of the air coming in the opening is going thru the radiator and not bleeding around, under, over it, you'll be amazed just how much better it cools at speed. I've spent days building/bending/riveting aluminum pieces to close off every bit of space in the nose of a car to improve cooling.

Fan on until it's proven not to be needed. Fans can still help up to and above highway speeds. The point where the fans no longer help is typically in the ballpark of 60-90mph for a production car, so a car needing them at 100mph is totally plausible. Looking at the stock ECU settings for a Toyobaru, it looks like it's set to turn off the fans above 84MPH.

I would still have a fan whether or not I use it.  Having a fan is better than doing headgaskets because you didn't have a fan.

Typical high performance aftermarket fans are rated at somewhere in the range of 1000-2000 cubic feet per minute.

If you assume a 1 square foot opening in the radiator grill on the front of the car, then at 30 mph you get (30/60)*5280*1 or 2640 cubic feet per minute of air going through that opening.  If you make sure that all of that air goes through the radiator rather than leaking out around the edges, then you have exceeded the performance of that fan.

Having the fan turned on at 60 mph is probably not going to help much, but it's probably not going to hurt much either.  What will hurt is having a third of the radiator surface blocked off with shrouding like in the picture.  I assume the little black things are vents, but you're still losing a ton of the possible surface area with the aluminum around them.

In reply to wvumtnbkr :

I could be wrong but the air would spin the fan as it's not locked in place. On my F500 you could visibly see the fan spinning when off.

Regardless I'm thinking leaving the fan on can't hurt.

In reply to Tom1200 :

Agreed.  But the air spinning the fan is taking energy out of the air.  That demonstrates it IS a blockage.

I don't truly think it's enough to be an issue unless the system is that close to the edge.

When we removed our fan (and fan shroud) from our champcar, we lost so much temp that we had to actually tape up part of the inlet to the radiator due to over cooling.  Granted, this was with a gargantuan radiator paired to a 180hp engine...

Now, if only there was a simple, reliable, inexpensive and easy way to turn that fan on and off when it was needed. Someday we will have that technology I suppose. Until then I guess we have to live with a switch on the dash and a meatbag behind the wheel with more on his mind than monitoring a gauge to control it.

Every time a car comes in with a manual switch on the dash I want to pull out a dymo and label it "Head Gasket"

In reply to Trent :

It's true, having a switch where the driver can force the fan off at all times is a very dangerous thing, it's very easy to forget. The only legitimate reason to even have such an option is for offroad vehicles where you need to force the fan off to avoid the risk of damaging it in deep wading. My Samurai has a 3-position on/off/auto switch for that reason and I've still forgot it a couple times, one time before a steep hill climb where I then had to manage how hard I ran the engine on the way up to keep it from overheating as the fan then had to fight a hot engine that needed to be worked hard.

A 20 amp fan at 12 volts is 240 watts, or like .3hp. I'm not good enough to detect .3hp loss, so I leave mine on as cheap insurance.

Shrouding wise, I've found that for a car that used to have a clutch fan, it sometimes works better to mount an e-fan into the original clutch fan shroud instead of using a common flat shroud.  It gets the fan further from the radiator which makes the fan work better, but it's also less restrictive at higher speeds, as the air doesn't have to make any tight turns to get from the radiator to an opening in the shroud to exit (regardless of whether it's going out through a flap or the fan).  The thin shrouds are very sub-optimal and in my mind, only for applications that can't fit a deeper shroud. 

Another point of concern is pressure buildup in the engine bay.  Some cars have trouble getting enough air out of the engine bay at higher speeds.  My Jeep was a good example of this.  Up to 50 mph or so, you couldn't get it hot.  But above that, the faster you went, the worse the cooling problems got if you were working it hard.  The simple answer to it was that most of those Jeeps came with clutch fans, but mine had an e-fan.  The clutch fan driven by the engine at 2000+ RPM could push plenty of air against the pressure buildup so they cooled fine.  The e-fan was more sensitive to output restriction (pressure) so it didn't really matter if the fan was there at all at higher speeds and natural airflow was insufficient.  Adding additional hood venting to relieve the pressure helped noticeably. 

In reply to Trent :

My Datsun 1200 race car has the original four blade nylon fan; it eats little power and it also eliminates the needs to wire anything up.  

Thanks for the chuckle Trent.  As I'm reading this I kept thinking that the main concern is fluid temp, right?  

If my car doesn't break at this weekend's autocross, I'll schedule a Track day and test the fan ON and OFF.

Might try to make a Oil cooler shroud like another post said as well. I think my oil cooler is about 3/4in away from the radiator.

My new shroud/Fan combo works crazy well compared to the LS1 fans set up I had before. (5lbs less too) The flaps 1/2 open at 35mph so I'll have to see at higher speeds if they fully open.