Oil Cooler(s) question

I'm in the process of putting a second cooler on my 3.6-liter equipped 73 911. I've got one cooler in the front passenger wheel well, and I'm putting a second one in the front driver's side wheel well.

I've always assumed that it would make the most sense to run the two coolers in series -- oil goes in the first cooler's inlet, then out from the first cooler through a line that leads to the second cooler's inlet, and then from the second cooler's outlet back to the engine. But someone recently suggested to me to run Y-fittings, to essentially split the oil flow and run half the oil to each cooler. This seems wrong to me, but I thought I'd solicit opinions on the board.

Opinions?

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Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net

[This message has been edited by JackOlsen (edited 01-16-2001).]

"3.6-liter equipped 73 911"

That sounds so nice!!

Jack,

What are the racers doing? It seems you should benefit from their experience.

Jack - I am planning to do the same with my SC using a multi-row heat sink type cooler followed by the Carrera type with a fan. What I have in mind is to run the coolers in series, but also run another stock thermostat assembly between them. That way the temp doesn't do wild ups and downs in colder weather. The multi-row unit does a fantastic job with the 3.0L, but I suspect it will be overburdened by the new motor.

[This message has been edited by RarlyL8 (edited 01-16-2001).]

Jack, I've never heard of anyone running a "Y" fitting before. That seems really funky. What you do have to worry about is the amount of oil, being able to bleed the air out, and any kind of pressure drop across the coolers. I have seen a couple of cars setup like you want to do yours with no problems. I have also seen some setup similiar but with another oil tank/pump setup under the front hood.(RSR's/CupCars etc) The size of your coolers makes a difference too. But, in the situations you use your vehicle, I think you'll be fine running it that way. Do you only have this problem when at the track? If so, an old racers trick is to remove the right front headlamp on track days.(and modifying the bucket) Some companies make a cover that fits in its place and has holes drilled in it so air will flow across the cooler better. Makes a big difference.(plus it looks better!!)
Marc

Marc (and others) -

I've considered the headlamp bucket trick, but have air currently coming in the horn grill, and also from a pretty big scoop underneath the spoiler.

The track is the only place I have any kind of a problem, but -- at Buttonwillow, in particular -- it's a serious problem. 15 minutes or so into a run, I'm pushing north of 240 degrees.

Series seems to make the most sense. I'm working on the assumption that the 3.6 has a pretty robust oil pump, and I'm running the oil first through a pretty free-flowing cooler (the Vertex one) and then through a Carrera cooler. Once it's all in place, I'll see how big a hit I take in oil pressure when the thermostat kicks in. If it's too much, I'll consider a second thermostat.

But I know other guys have done this successfully. I'm going to continue on the series path.

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Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net

The person that suggested running the coolers in parallel may have been thinking that the 2nd cooler would be more efficient compared to running in series. The second cooler in series would have a smaller temperature difference between the cooling air and the oil. With the parallel setup the oil temp going in would be the same at both coolers. The bigger the temp difference between the air and the oil, the more heat energy the cooler is going to reject to the air. I would also think the pressure drop across two coolers in parallel would be less then two in series. This would put less strain on your oil pump.

Hope this helps,

Pat

Jack,
Have you thought about just adding one bigger cooler? It seems to me if you are after surface arear for cooling a bigger cooler just might do it.
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Paul
78SC Targa

Just a dumb engineers opinion:

Efficiency of any coolers raise
a)with the temp difference and
b)the flow speed of the medium.

Therefore, a Y-fitting makes sense for a), but not for b). I don't think that you can judge correctly the influence a priori.

To get around the problem, I would also use a larger cooler or a higher air flow by using a better fan for example.

Jens

Jack,

I tend to prefer the series connection, because it is simpler, and because any kind of juction connector can add restriction and turbulence to the flow, and some are just horrendous!

Just one reminder, the 550 Spyder (and Carrera 2 in the 356 body) used a series cooler, and it had a scavenge pump much, much smaller than even the very first 911 ... and also made up to 200 hp DIN in some incarnations! And, I suspect the factory racing engineers had a free hand to do it the way they wanted, dictated only by testing and racing demands!

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Warren Hall
1973 911S Targa

Series it is.

I'll post pictures when it's all together. It will get its first test on the 27th, at Streets of Willow.

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Jack Olsen
1973 911 T (3.6) sunroof coupe
jackolsen@mediaone.net