Budget Oil Cooling - Myth Dispelled

[unclebilly]

My 77 with a pseudo 2.7RS engine has been running really hot at the track this year. After 5 - 10 laps depending on the track and the outside temps, it would be close to 250F.

I tried to fit a carerra cooler in between the bumper and the bulkhead but i couldn't make this setup work.



I bought an RX7 oil cooler for $50 and mounted it in my front airdam. I cut one of the bottom loops out of my trombone cooler and connecteed on to it with 7/8" tubing X 3/4" NPT connectors from Home Depot. I did not remove the thermostat from the rx7 cooler and did not modify the tanks or the banjo fittings on the rx7 cooler.





The cooler works just fine as it is, my temps sat half way betwen 175 and 210 all weekend (3 days of racing). There is a 30°F delta T across the cooler (see pics) and this is when I get back into the paddock so going hard, it would be more.







I guess the point of my post is that you don't need to drop $600 on a setrab cooler, you don't need to modify the rx7 cooler, and this can all be done for under $100 with custom made hoses and fittings.

[dentist90]

Cool is... cool!

[rouxroux]

Nice work! Always fun to do your own engineering.


(now add a cool collar and you'll have an icemaker)

[aston@ultrasw.c]

Nice work!

I love the $100 solution to a $1,000 Porsche problem.

So is it a Mazda OEM part, or an aftermarket part intended for an RX-7?

Also part numbers would be useful.

Not sure about using hardware store fittings on something as critical as oil system. For example Russell fittings from Summit Racing are not that expensive and were designed for this type of application.

[jpnovak]

Great idea with the compression fittings on the trombone cooler.

[mca]

Congrats. Wow, what a drastic change in temps. And it is a thrifty solution!

[JFairman]

They are the origonal oil coolers on older RX 7's.


They are well made but the oil line fittings are alot smaller inside diameter than Porsche uses.
I think the RX 7 thermostat inside the oil cooler should be removed or modified to stay open if you have the origonal Porsche external thermostat in the rr wheel well.

[DW SD]

I read a thread by Don E in the 930 section where he said the diameter of the oil line within the factory thermostat is just 7/16". Doesn't mean you can run 7/16" line and be OK, but it is worth noting.
I wonder how you can tell if the scavenge oil pump is loading up due to the increase in head (from restrictions)?

Great solution!

Doug

[Wyvern]

Would it work the same to install the RX part in place of the trombone?
& I can't find cool collars

[JFairman]

"I read a thread by Don E in the 930 section where he said the diameter of the oil line within the factory thermostat is just 7/16"

I read that too...
I think another opinion on that is needed.

Just because one guy on a message board that's already confused by his cars oil thermostat looks in there or dissassembles it and thinks what he can see is a 7/16" orifice or passageway the oil has to go through means little without more research and proof.
You need to know the flow rate and looking at it doesn't tell you that.

Like is that assumed 7/16" opening round, square, the height a round valve has lifted or moved off a seat or what?

All that said people have been putting RX7 oil coolers on 911's for around 35 years now so it's doable.

I don't know if a 930 scavenge pump moves more oil than a normally aspirated 911 oil pump. It's alot bigger so I think it probably does.

[juanbenae]

subscribed! rx7 units available new or ar a wrecker?

[Formerly Steve Wilkinson]

Wyvern, Cool Collars is a joke. It's an aftermarket finned aluminum heat sink that wraps around the oil filter, and everybody here makes fun of it, though the joke is gettin' old. Worked fine on my airplane (Lycoming engine) but the filter there is in the cooling-air blast, though I do indeed still have it on my 911.

The argument against putting it on a 911 filter is that it indeed sinks heat away from the filter, but then simply radiates it into the engine compartment, where it raises the heat of the air going into the fan some minuscule amount. Big deal, but it is probably true that it actually does no effective "cooling" on a 911, with its semi-sealed engine compartment.

[DW SD]

Originally Posted by JFairman

"I read a thread by Don E in the 930 section where he said the diameter of the oil line within the factory thermostat is just 7/16"

I read that too...
I think another opinion on that is needed.

Just because one guy on a message board that's already confused by his cars oil thermostat looks in there or dissassembles it and thinks what he can see is a 7/16" orifice or passageway the oil has to go through means little without more research and proof.
You need to know the flow rate and looking at it doesn't tell you that.

Like is that assumed 7/16" opening round, square, the height a round valve has lifted or moved off a seat or what?

All that said people have been putting RX7 oil coolers on 911's for around 35 years now so it's doable.

I don't know if a 930 scavenge pump moves more oil than a normally aspirated 911 oil pump. It's alot bigger so I think it probably does.

JF-
Good points. Until documented, it is worth not taking it for the gospel, but it is an interesting observation which would be easily confirmed.

Doug

[JFairman]

Hi Stephan, you should recognize this oil filter...
It's the system 1 oil filter you gave me a few months ago.

I have it mounted in the charcoal cannister bracket in the top of the right rear fender well. It's plumbed into the turbo scavenge line after the turbo scavenge pump with 7/16" ID fuel line so it is filtering the oil that comes out of my turbo on my '87 930 before it goes back to the oil tank.

It makes good use of that charcoal cannister bracket. I didn't have to drill any holes in the car to mount it this way and it works great.

thanks again!

Jim

[Formerly Steve Wilkinson]

Excellent! Delighted you could use it.

[JFairman]

You can't see it here but I glued a 1" wide strip of tapered rubber onto the inside surface of the the stainless steel strap with weatherstrip adhesive and also the base part to grip the filter in place better than it appears here.

It fits in the bracket pretty well.

[Wyvern]

Thanks "Formerly S W"

I did have Cool Collars on the rock crawlers and, they worked and, protected the filter.

Would you give a thumbs up or down on the Tank to Cooler units ?

(Dont I have some info to return to you ?)

Thanks for letting me hijack ... But I also was just under 250 deg on the way back from Monterey this weekend (ambient temp around 100) so looking for solutions and liked this one.

[Wyvern]

Like this one on Flea Bay ?

86 to 91 RX 7

[rnln]

Great news. I wanted the RX7 cooler but always affraid of the termostat thing and the small opening (volumn of oil flow) which people have been talking about.
Could I have some questions regarding your home depot fittings on the below pic?
- do you have to do any welding or soldering or just cup on the copper thrombone?
- What is thesmallest inside diameter opening of those adapters and your hoses fitting ends?
- So you install it right behind the airdam? How about behind the stock bumper. Will it fit in there without modification?
Thanks Billy.

Originally Posted by unclebilly

[Walt Fricke]

I am a fan of the RX-7 coolers. Have always gotten them used, though I think they can be purchased new for a reasonable figure. One attractive feature is that they (one common type of them, anyway - some are smaller) are a good fit for the standard center cooler cutout on aftermarket front spoilers or spoiler/bumpers. New removes the worry about nasty debris that might be in the cooler. Maybe RX-7s never blow up?

These coolers hold up well when untoward incidents happen on the track. I've had two mangled (hence the experience of prepping and installing three), but they never leaked. Were probably still functional despite twisting.

I, too, see no reason to retain the RX-7 thermostat. If you remove it, you can go in through the hole that is left with a tap (1/8"? pipe thread - I forget, but it is obvious) and tap the hole that goes between the inlet chamber and the outlet chamber. Then screw a brass or aluminum pipe plug in to block that passageway.

I've always had AN fittings welded on, thinking the stock holes too small. But maybe (as this experience seems to show) that was being too cautious. One thing this did allow me was to position them so they pointed exactly where needed. I use the spoiler that has brake duct openings, and getting by those means the stock holes are not really well positioned - at least one of them is not. But an angled fitting in the stock location ought to do the trick. And maybe with banjo fittings this isn't an issue at all. Best to trial fit things before doing any parts purchases (or welding) anyway.

I'll disassemble a factory thermostat I have sitting around to see if I can determine the area of the smallest orfice through which oil would have to travel to get to a front cooler. Pictures, too, maybe.

Is the flow capacity of a system restricted to the smallest orfice? Would that mean you were not getting more flow with larger lines, if there were a smaller choke point somewhere? Or is this like electrical resistance - you add the resistance of a short small section to the resistance of a long larger bit?

Clever work here, anyway.

Walt Fricke