Rear decklid oil cooler?

[ibmiked]

I was considering purchasing a rear decklid oil cooler as a cost effective way of adding extra cooling capacity to my car. A search here brought up zero results (that I could find) of this type of system. Does anyone have any experience with how well these work? I'm not ready yet to add a front cooler, and with my 2.0L I think a rear cooler might just be all the 'insurance' I need.

Thanks for any input.

Mike

[304065]

Mike,

For oil coolers to work properly, they need to be in a high-pressure airstream. I always chuckle at the folks who put NACA ducts on the side of their cars- NACA ducts are intended to permit airflow but not screw up the boundary layer at high mach numbers. If you want high-pressure airflow, you need a big honkin clamshell kind of scoop. Maybe not even so big-- maybe a little scoop like the avionics cooling scoop on the side of a Cessna 172, only slightly bigger.

Airflow through the grille is prodigious, something like 1390 liters per second through the fan, that is 2800 CFM to you and me. If the engine compartment above the tin is sealed tightly, then the airflow should be an approximation of that.

But here's the rub: hanging a cooler in the cold air going into the fan is just going to heat the air up. Being less dense it does a worse job of cooling the fins and engine cooler, so you probably end up with higher temperatures than lower.

I know the Factory put the condenser for the a/c system there. I know they also put the intercooler there, probably the last thing a Turbocharged engine needs.

However, if you want better cooling, why not spin the fan faster? You may need a different engine cradle to accomodate the larger 134mm pulley, but for a man of your skillset this is minor. I've done all the math, don't worry about mach overspeed. The factory upped the fan speed on the Turbo-motor and you can too.

Why can't we make the engine cooler larger? Well you can see the oil inlet tube gets in the way.



Do you have a 70- fan shroud on the engine? The later shrouds had a channel to direct cooling air to the engine cooler, vs. the earlier ones that are just flat. With the horsepower going up the Factory did take measures to enhance cooling. Call Damon at Series900 and have him make you one.

Did you do the engine tin Mod?

[ibmiked]

John,

That is precisely the kind of considered response I was hoping for. Great idea. Will the alternator need any modifications to accommodate the additional constant higher RPM?

Thanks,
Mike

[ttweed]

...with my 2.0L I think a rear cooler might just be all the 'insurance' I need.

Why do you feel you need "insurance," Mike? Are you suffering from overheating problems? Is your 2.0L modified/hopped-up? The stock early engines don't make the kind of heat that the later, larger displacement engines do. My old '67S did hundreds of thousands of miles in all kinds of conditions (including desert and track driving) and never saw unacceptably high oil temps. Porsche didn't specify an auxiliary oil cooler for the 2.0 street cars because they didn't think they would need them in normal use. The engine mounted oil cooler should be sufficient if everything is working properly, IMHO.

TT

[Reza]

There was also an early attempt at a rear wheel well mounted oil cooler, I saw it somewhere.

[ibmiked]

John,

I have a '68 fan shroud and haven't done an engine tin mod, I'll look into that for certain. (EDIT): Actually now that I think of it, the shroud does have a riveted channel on the underside. Is it that of which you speak?

Tom,

I asked not because I'm having a problem, but merely because I'm looking for a bit of 'insurance' and saw the deck lid cooler come up for sale at a very reasonable price. I haven't got much 2.0L driving time under my belt, but my local group of hooligans are generally 3.0's and 3.2's, so I know I'll be pushing the car hard this summer to stay on the pace. I'd rather build in some excess cooling capacity now as opposed to confronting a potential problem mid-season.

Rez,

I saw Bob Tilton had a thread about that. Interesting to consider for the future...

Thanks for the food for thought guys.
Mike

[912-2.8]

Mike:
I'm converting a 912 to a 2.8 so I have a 'clean sheet' so to speak and have been looking at a rear cooler as well.

You need to poke around in the rally pictures. There are a few interesting ideas out there. Since I'm on my iPad I can't post them now. I'll try to tomorrow.

I've seen three schemes:
1. In the rear engine lid. Factory did this on the rally SCs, but as mentioned I'd rather not preheat the cooling air.
2. Cut away all or some of the rear crossbar where the latch mechanism is and add a cooler with a slot in the lid to feed it.
3. Rear fender trombone cooler. There is lots of junk here so the trombone seems smart.

I've personally wondered about a scoop on the rear fender much like the Alpine A110s typically have that ducts out under the turn signal. 912, so no oil tank there :-). I'd use a 993 cooler sideways so it doesnt fill with tire/road crap.

Finally, I've been wondering about using a Gurney lip on the very bottom of the engine lid rather than the standard duck tail position. This would allow use a long, thin cooler just below, and get the best leverage on the aero. I've never understood why the factory duck tail is so high up.

tadd

[hoffman912]

I asked not because I'm having a problem, but merely because I'm looking for a bit of 'insurance' and saw the deck lid cooler come up for sale at a very reasonable price. I haven't got much 2.0L driving time under my belt, but my local group of hooligans are generally 3.0's and 3.2's, so I know I'll be pushing the car hard this summer to stay on the pace. I'd rather build in some excess cooling capacity now as opposed to confronting a potential problem mid-season.
Mike

on my measly 1.7 four banger, i have to keep up with the same kind of crowd. I have an aluminum oil cooler in the stock position, and a full flow oil filter in the wheel well. The location of it makes it act as if it were a psudeo oil cooler. result? my temperatures rarely go above 1/4 in normal driving, when chasing everyone on mountain roads with my foot burried to keep momentum up its only about 1/3 (you have seen how hard i drive mine and keep up with you guys). and in the mojave on cross country trips, maybe 3/7 if that. i know its not apples to apples, but i would think applying a true rear fender mounted oil cooler could be all you need.

i would be hesitant to mount something to the lid.. kind of ugly and you preheat the air coming into the fan. I wouldnt modify the rear cross bar or anything else that is in view. If it were me, i would go with a rear fender mounted oil cooler. plenty of cooling, clean install, proven effective results that you dont have to rewrite the book on or re-engineer to make it work, and parts are probably readily available (maybe cheaper because of that?)

[adam912]

Harry, got any photos to post of how that full flow filter mounts on your car?

cheers
Adam912.Out.
'66 912, 485,000 miles, 2.2L T4 power!

[beh911]

Re: 2.0l cooling

Just echoing that I think you will be surprised at how cool your engine runs compared to larger displacement examples. The thermal stress on a 2.4+ is much much higher than a properly built and/or tuned 2.0.

My car has the S front cooler, but even then I only noticed it warm to the touch on a couple occasions last year. The cooler circuit opens ~180F. This was through the silly hot summer we had in ATL.