Transmission Coolers

[widebody911]

I've decided that I want/need a transmission cooler, but I don't want to tear down the tran$mi$$ion at thi$ time.

AutoMetrics has a cooler kit - anyone have experience with them or their design? Like most vendors, emails to the address on their web site go unanswered.

I don't think I'd mount mine in this location, but once you had the plumbing and pump in place, you could pretty much do whatever you pleased.

[Bill Verburg]

The objection I've always had to that design is the missing internal spray bar. I can not speak for Autometrics specificly, but in general in these types of devices only the external cooler part and pump is in place, this is good as it does cool the transmission fluid, but the other half of the proper design that the factory used on their high power/endurance designs is an internal spray bar which specifically sprays pressurized oil on to the gear clusters and at the ring/pinion, rather then the splash lubrication normally used in the 915.

Interesting note , splash lube in the 915 absorbs 7hp at max speed.

[cary]

I'm with Bill. This is one of those come big, or don't come at all projects.
If your spending quite a bit of time at the track. You need to have it done correctly. I'd go here and look at a couple examples.

www.rennsportsystems.com/~porsche/

[Jack Olsen]

I disagree that the cooler should only added in conjunction with a spray bar. Having both is better, obviously. But I can't see any harm coming from only lowering tranny temps.

I think using the drain hole for plumbing it is a little dangerous -- although I did it with my previous setup. It's very low; only the sway bar mounts are lower. You could shear it off and not know you're draining your tranny dry.

And although Steve Weiner (a guy who knows Porsches only about, oh, a thousand times better than I do) recommends putting the cooler under the decklid, this strikes me as not the best place for it. First off, you're going to be adding some heat to your engine when the pump is operating and the tranny is hot. And you're also creating a situation where the lines for the cooler need to flex regularly, as they're moved whenever the decklid is raised. Obviously, these are both fairly minor points, but I still think there's a better argument for putting the cooler in those big wide fenders, on your car, where you can duct in air if need be, for the 1% of the time that you'll actually need this thing.

If you were putting together a race car, I'd say you should definitely get the full sprayer setup. There's no good argument against it. But for occasional track use, I think there's a good economic argument for a simple pump and cooler.

[Bill Verburg]

Jack, I didn't say it had to be used with the spray bar, just that it was better and that I had not used one because I was holding out for the more thorough solution, do it right or not at all is my motto(spend more $$ is more like it). I am still searching for the right trans as a spare for when and if?

The factory ran their lines on the early RS and RSRs up the left side of the car to the drivers side fender well where you(Thom & Jack) guys have place your second oil cooler, so thats out(unless there is some room in front of or behind the existing coolers). The 84-86 just stuck the cooler out the side of the case relying on the air flow by the bottom and side of the trans case. The next most obvious spot is where Autometrics placed theirs, in the lid. Again I agree that its not the best but maybe as a compromise?

[cary]

I think you need air pushing thru the cooler to get it to work efficiently.
I agree with Jack, adding heat to the engine compartment is not a good thing.
But just hanging it out in stagnant air isn't going to cool very efficiently. All it is doing is becoming a heat sink. Not a cooler.

[Jack Olsen]

You're right, Bill. Both is better. We agree on that.

I have both my trans pump and cooler (a 951 oil cooler) in the front portion of the driver's side rear wheelwell. I like that it's not adding weight behind the rear axle line, and -- even without any ducting -- it did a good job on my 7:31 915. For a recent trip to Willow Springs, I zip-tied in a Home Depot aluminum ehxaust pipe for a clothes dryer. It's the opposite of elegance, but it kept tranny temps even more flat on a fairly hot day. To my mind, this is the best place for the pump and the cooler. (Then again, I just had to replace my transaxle, so take everything I say with the appropriate grain of salt. )

I'll be testing the new transaxle next weekend with the same pump and external cooler (but also with the sprayer bar). It will be cooler (probably 70s or 80s), but I'll let you all know about the temps. It's at Laguna, which involves a lot of winding the car out in third gear. If the scoop and duct arrangement continues to make a difference, I'll engineer something more discreet to bring the air up.

My "for testing purposes only" scoop:

[Bill Verburg]

Looks good!, keep us posted, where did you get the trans?

[Bill Verburg]

Here is another clean electric pump installation for trans fluid/cooler. They also installed the internal sparay bar. The owner reports that even in an Enduro(Watkins Glen) he does not turn it on. Car is a 3.2 liter F-trooper.

[TRE Cup]

Jack's current transmission has a set up that sucks the lube from the bottom of the case (not the drain plug) , sends it thru the Jabsco pump (like most shown here), thru a 944 Turbo engine oil cooler in the left quarter panel (in front of the l/r wheel) and back into the spray bar that hits the gear clusters and r/p. It has a thermal probe that actuates the pump when it is up to temp.

[Jack Olsen]

Yes. The "Home Depot cooler scoop" it should be noted, was my amateur engineering, not TRE Motorsports'. It got sheared clean off in an off-track adventure this weekend at Spring Mountain.

But the new tranny never got above 220F all day -- and that was only when I deliberately disabled the temp-activated pump.

[Bill Verburg]

Jack, Any detail pics of the setup. I'm particularly interested in the temp sensor part. I have acquired a 915/67 and am considering monitoring the temps.

[Clark Griswald]

Jack,

Looks like a nice setup. What temps did you see with the pump on? What was the air temp?

How hot where temps running in the heat of the summer?

[Jack Olsen]

I can't get more specific photos for a few days, since the car is getting some details taken care of at Dave's shop. The previous 7:31 tranny ran hotter, even with the pump on. Max I ever saw (without the pump) was 260 degrees, which is too hot, clearly. The pump got it closer to 220, but I wonder if any components of the earlier box's design made it more susceptible to heat. One clear possibility is that the old box had a ZF limited slip unit, whereas the new one is the torque-sensing type (by Guard Transmission).

The old setup scavenged through the drain plug and re-filled through the fill hole. The new one is better plumbed, with the spray bar and its own holes. I think there's even a special port for the temp sender, now. The temp-sensitive switch is just a J.C. Whitney model, which has a manual adjustment dial on it for where it triggers. The sender is simply strapped to the bell housing. I have an override switch in the cockpit.

I'll post some picutres as soon as I can.