oil coolers and t-stats, do I really need 'em Options

[Trekkor]

I plan on putting that small SIX in next month.
I've been reading old threads on the subject.
Some name builders say no t-stat.
My SIX has the on motor cooler already.

I am considering the RX-7 cooler, but do not want to modify it. Are the inlets too small as is?

I plan on hitting the track on some level next year.
Is that the deciding factor?

Would it be best to just mount the cooler with t-stat and forget about it?

Tell me what you've done and...
(IMG:style_emoticons/default/thisthreadisworthlesswithoutpics.gif)

KT

[swood]

Good question. I was thinking about the same question (for a /4 though) earlier. I saw someone posted a picture of the flap over the #3 screwed down on the case. Making room for my Mallory tweaked the tin and the flap on that side is sticking a bit. Ithought I'd just put it in the full flow position. It's not like it's every really cold hear anyways for warm up...

[J P Stein]

My 2.4L T (140 or so hp) ran justfinethanx without an external cooler.
I hab no pics of no cooler. (IMG:style_emoticons/default/confused24.gif)

Mr. Anderson says 170 hp (or so) & it's time for an external cooler on a 6.
He would know......

[Trekkor]

So, maybe I get it in, dyno time, and then make the decision?

KT

[nebreitling]

my opinion ain't worth much, but if i were going to track the car, i'd go for the cooler as long as i was at it.

n

[Dr Evil]

I'm right on the cusp of 170 hp (or will be when the engine is together) and have heard yes and no for this range. But, for the engines smaller than the 2.7 I have heard way more no answers. Unless of course you have higher compression or something. Also, I was told to use either AN12 or AN16 lines, and the fittings on the RX7 cooler are banjo type stock so you would likely need to modify it to the AN. I have a grip of pictures for various ways of installing such things if you need.
HTH

[J P Stein]

What I *would* suggest at this point is using Aeroquip lines for the scavenge side return line. You can (and I did ) cut & paste at a latter date ....with minimal hassle...should you need to go to an external cooler.

[Martin Baker]

Trek, why would you not run a thermostat? Air/oil cooled engines should run at a constant temp like any other engine. Without you just shorten the life of the engine. Track=cooler, when its 80-90 degrees here in the summer, so too is you oil, before you even twist the key, so I don't see the need for these questions, I think you answered them when you set your parameters...I am sure others will think otherwise, but I know whats in my wallet.

[ArtechnikA]

you won't need a cooler on the street unless you have retained the 914/4 'ZD' 5th gear and insist on using it in the 55-65 mph region. there is more than one reason 914.6 came with the 'ZA' top gear.

you won't want it for AX - most of us have a hard enough time getting the oil as hot as we'd like, especially for the first run. this is one reason i was planning on building in an electric tank-heater for my car - i have attended a few AX's when the first runs were made in the low 40's...

but for sure you'll be glad you've got it on the track, especially if two are driving.

i would NOT use an unmodified RX-7 cooler -- and i'd look very carefully at the bottom line considering all costs (acquisition, ultrasonic cleaning, modification...) compaaring to an appropriate NEW FluiDyne or, if that's looking pricey, SerckSpeed from Earl's.

go read Anderson's section on oiling systems again, especially since you may not knw if your case has had the scavenge mod and/or what oil pump you are running... ask Bruce or Jerry in person what size lines you should use and they'll say AN-16 -- they kinda regret saying -12 in the book -- but a lot of guys use AN-12 with no problem. if your budget forces you to use -12 to the front, i'd at least use -16 on the run to the thermostat and back.

i would definitely use a thermostat. check out the oil systems sizing and specification chart in the Elephant Racing catalog (available as a PDF on their website) -- it's excellent (and there are pictures...) use either a '72 911 TStat or a Troutman.

in addition to the temperature regulation issues already covered in this thread, it takes a lot of work to pump cold oil at high pressure to the cooler and back (power loss) and hitting the cooler with high oil pressures is not good for it. for this reason - keep the Tstat at the back, with the engine, not up front, with the cooler.

JP's advice about plumbing the scavenge line is excellent.

[IronHillRestorations]

I agree with Bruce Anderson's 170hp recommendation, but maybe a little lower for a 914-6.

If you are right on the borderline, then plumb it so you could add one if your oil temps stay too high.

In CA, you probably do not need a thermostat for an external oil cooler, unless you are going to operate the car below 45*. If you plumb it on the pressure side, it has already passed through the internal thermostat in the engine. It wouldn't hurt to have one, but you probably don't need it in Napa. Also don't wind the engine above 4500rpms until it reaches operating temp.

On the last conversion I did (Don9146) we got a cooler with a fan from The Latest Rage (a VW part house) for fairly cheap.

[J P Stein]

If you plumb it on the pressure side, it has already passed through the internal thermostat in the engine. It wouldn't hurt to have one, but you probably don't need it in Napa. Also don't wind the engine above 4500rpms until it reaches operating temp.

I'm a bit confused on your reference to "pressure side" as it relates to an external cooler. Perhaps you could expand on this a bit.

As for keep it under 4500 rpms till up to operating temp....I wish I could. (IMG:style_emoticons/default/sad.gif)

[ArtechnikA]

I'm a bit confused on your reference to "pressure side" as it relates to an external cooler. Perhaps you could expand on this a bit.

As for keep it under 4500 rpms till up to operating temp....I wish I could. (IMG:style_emoticons/default/sad.gif)

the factory cooler is on the pressure side. Anderson talks a bit about this....

pressure-side coolers are LOTS more effective because they are cooling oil, rather than foam, like the scavenge coolers are.

you can use the 993 takeoff fitting or a purpose-built fitting. factory race cars almost always used a pressure-side filter there in place of the street in-shroud cooler, since thay all had huge front-mounted coolers.

as for regulating idle during warmup, you set the hand throttle, and go get a cup of coffee... :-)

[Trekkor]

Thanks for the advice.

Do I understand correctly that I can try it without the t-stat and cooler and add them if it runs too hot?

KT

[ArtechnikA]

Do I understand correctly that I can try it without the t-stat and cooler and add them if it runs too hot?

of course.

people add front oil coolers to 914.6's all the time.

what you -can- do, as JP observed, is prepare for it by using a scavenge return line that is built for this purpose. for instance, using the appropriate fittings on case and tank to let you use an AN-16 hose, probably with straight hose ends and a union connecting the two ends. i don't know exactly where that 'break' ought to be, but it seems like it would be as close to the tank as practical. (this was JP's idea, i'll let him elaborate...)

so you can gradually build in the infrastructure. decide how you'll get air to the cooler; decide how you'll get exhaust air away from the cooler (didn't we just have this discussion?) buy the cooler, mount it in, get the thermostat, mount it, measure how much hose you'll need (more than you think, once bend radii get into the picture, and those fittings always take up way more space than you think...) get the fittings, mount them up, measure the hose needed to connect. make up the hoses. then one day, you can cut over and plumb it in.

[Trekkor]

Nice...Good ideas. (IMG:style_emoticons/default/clap56.gif)

Pics to follow next month.

KT

[IronHillRestorations]

[QUOTE]I'm a bit confused on your reference to "pressure side" as it relates to an external cooler. Perhaps you could expand on this a bit.

Perhaps I'm not using the correct terms. I call the line that connects to the bottom of the tank (in the bottom of the fender well) and goes to the tube on the bottom of the oil cooler the suction side. And the side that comes out of the side of the crankcase the pressure side.

[ArtechnikA]

I call the line that connects to the bottom of the tank (in the bottom of the fender well) and goes to the tube on the bottom of the oil cooler the suction side. And the side that comes out of the side of the crankcase the pressure side.

aha.

i think we'd all agree on your use of the term 'suction side.' - that's the inlet to the pressure side of the oil pump and not a good place to plumb any kind of restriction.

what you've called 'the pressure side' tho is what most of us call the 'scavenge circuit' -- that's the output of the scavenge pump, and is the line most-often used to feed a thermostat/cooler (since it is hottest, and the scavenge circuit is less critical.)

scavenge oil, tho, is pretty foamy, which makes it less efficient to cool.

the factory on-engine cooler is in what's conventionally called 'the pressure circuit' - that's the circuit that runs from the inlet (the suction line) from the tank through the pressure (smaller) side of the oil pump, to the stock thermostat, and possibly through the on-engine cooler before going to the bearings.

since this oil has been de-aerated by its trip through the oil tank, cooling is much more efficient.

the factory race cars (and 993) put another filter there instead of an on-engine cooler. there are port plates available that bolt up in place of the stock cooler and let you run whatever additional pressure-side filtration and cooling you require. all 993 and factory race cars have BIG front mounted oil coolers, and the 993's incorporates at least one fan to cool the oil in traffic.