Oil Cooler Air Flow Question

[jameshtaylor]

My 2.7 has a front fender mounted Earls cooler (as big as I could get in) with bigger than stock -16 ilnes to and fro. There are no additional holes in the body to let air in to the cooler, so the oil cooling I get is mostly the result of the oil going fore and aft in lines exposed to the air, plus whatever heat is dissipated by the oil cooler itself.
Because I sometimes see warmer temps than I like, I've been considering adding a fan. I was skeptical that it would make any difference at track speeds (traffic isn't an issue for me) but some of you have said a fan should definitely get me 10-20°, which would be great.
The obvious place to locate a "pull" type fan is behind the cooler itself. But I have a serious clearance issue...a very thin 2" SPAL fan won't clear the tire. So I thought, why not mount the same "pull type" fan in front of the cooler. Since there is no air flow from the front of the car thru the cooler that the fan would be "fighting", I'm wondering why this wouldn't work. Any thoughts?

[MoparBoy72]

On my DD, I have a 5.2" SPAL fan on my trans cooler. It is a "pusher" and works fine.

[Greg D.]

Push or pull, I have a such a fan on a an upgraded cooler on my SC, and it makes very little difference on track. It does make a huge difference in traffic, but not on track. For the track, cutting the headlight bucket and removing said headlight is probably your best bet, short of the "only solution that really works" the bumper mounted cooler ;-) (or a pair of 993 coolers, but that is expensive)

[jameshtaylor]

Thanks to both of you. I have heard so many conflicting opinions about fans on track I guess I'll just try it and see for myself.
My "radiator" measures roughly 8 x 12 = 96 sq inches. A 10” fan will 'cover' 75 sq inches or about 3/4 of it. I figure that if I could get my 96 sq inch surface into clear air, at 1 mile/min it would get 96/144 x 5280 or 3520 cubic ft per minute of cooling. A 10” SPAL fan will supply 650 CFM to ¾ of the exposed area, so it should be 650 /3520 x ¾ or 14% as effective as clear air. What the effect of this cooling is on oil temps (if any) compared to the zero air circulation I now have, is a guess. But if running the radiator in clear air would drop oil temps from 250 to 200, as some have reported, maybe I could get 14% of this 50° reduction or 7°?

[davep]

Fans are much more likely to be effective in slow traffic than on a track. Take a look at the fan specs for air velocity, say in feet per minute. Calculate what that is in miles per hour. Basically any descent speed will exceed fan velocity at which point the fan becomes more of a liability than an asset. Worse, if the fan blade does keep up with the velocity of the air being rammed through it, it could damage the fan bearings.

[jameshtaylor]

Deja vu all over again. This is exactly the argument I made on another thread a couple of months back. But several people pointed out that there is virtually NO air movement under the fender without an open headlight bucket or some big air source and thus the fan would help. THere are people here who swear noticeable improvement from fan use at the track; I myself am a skeptic but it doesn't cost much to experiment.

[edmayo]

James, before you get too radical here your solution may be much simpler. As is often the case the Porsche engineers were not stupid, we just need to understand what they were doing and how they did it. My 72 S has the standard factory front cooler set up. On hot days, (over 90 ambient) if you're really flogging it on a race track DE event the oil temp might get as high as 220. Freeway driving at the usual 85-90 mph on 95 degree days it will maybe get as high as 195. Now granted you have a 2.7, which will make more heat than my 2.4, but I also suspect that when you installed your cooler you didn't use the louvered plate that is on factory installations. That plate is more than a stone guard, the air flow from tire rotation creates a low pressure behind the louvers that helps to improve the air flow through the horn grills. Now I realize your 74 doesn't have the horn grills, but if you were to cut a slight notch in the valence just below the bumper it would significantly improve air flow. (look at a late 80's 911 Carrera the underside of the bumper is even formed to help air flow)) You'll also notice that the louver panel is sealed against the underside of the fender, there is no place for the air to go but through the cooler. If you don't have that sealed, the air just simply goes around the cooler.(path of least resistance) I suspect that if you just had the complete factory cooler/louver set up without any fans, the temps would be well in range.

[Chuck Miller]

Ed,

I'm sure glad you shed some educted light on this issue...

I've retro fitted a '72 cooler and shield (w/ late lines and thermostat) to my '73S over 15 years ago with the very same results and temp readings as you....

I've also been around the under-front of my car while the tires/wheels have been 'spin balanced' and I'll tell'ya what... those front tires are pumping out SO much air it's hard to get your hand even close to'm...

Thanks for the experienced reply bud.......

Cheers and happy Holidays

[edmayo]

Thanks for the kind words Chuck, and Happy Holidays to you. Got my registry calendar the other day, you guys did great on that one, going to enjoy looking at it for the next year much more than the animal one from my insurance agent for last year!

[jameshtaylor]

Thanks to both of you. Let me clarify a couple of things. My cooler (with bigger than stock AN-16 lines fore and aft) works well, even in Ft Worth-like temps. In 100° ambient on a long ten mile hill I rarely see 215°. At the track in similar temps the car will get near 230°. It was a long dialogue with Steve Weiner about a year ago after a serious top end problem that convinced me that anything over about 210° (with the mag case) is to be avoided if possible. So I am searching for maybe 20° on the worst days I face.
I would think the notion of adding something at the bottom of my cooler to help force the air through it would be worth at least a couple of degrees, so I'll tackle that, and I'm intrigued with the idea that the tires pump a lot of air around the fender well. Clearly that at least gets rid of whatever heat is radiated by the cooler.
I also like the idea of a bit of airflow thru the front valence. It looks like I could easily get a 2" x 9" slot there, (just under the bumper to the left of the opening for the brake cooling duct) which should deliver about 19% of what the cooler would get in clear air, enough to make a difference I would think.
Wonder if anyone has a picture of such a vent? Cutting out the back of the headlight "box" is common enough but I don't think I've seen this done.