Ducman82

SITREP:

Moved to LA. Traffic sucks. i have no oil cooler. thinking it needs one now.
i have one of carls radiators but no oil cooler option. So my options are... (i think)

New radiator with internal cooler

New radiator with internal cooler AND later style air to air cooler in front.

Stand alone radiator with fan in fender well. thinking this one http://www.carshopinc.com/product_in...FQmSfgodh1kAFw


what if any other options are out there? what have you guys done?

huskeric

There was a post on here not too long ago about adding an RX7 oil cooler. While it was specifically aimed at racing, this would also work great in stop-and-go traffic and the high heat in Vegas.

This oil cooler option - or another variety - would be less expensive than another radiator.

Let me see if I can locate the other post...

-- located --

https://rennlist.com/forums/928-foru...track-car.html

rick

Alan

Air/oil is not good on its own for crawling in traffic (OK for racing) - how could it be? - there is no airflow - this isn't assisted by the rad fans. The stock late model air/oil doesn't work well at all at slow speed with hot ambients (esp. after a high speed run).

Jake you need some kind of fan cooled solution for this - either a new radiator with side tanks or a separate dedicated fan cooled version like you showed. Air/Oil is probably good in series (before) the side tank for a rad side tank config (reduces max thermal load @ speed).

However the one you showed would probably work just fine on its own. You'd need the fan controlled by switched power and a thermal switch on the oil cooler itself. Funneling air to it for at speed conditions would be good. Should be a lot cheaper & easier than a new rad.

Alan

Adamant1971

The early rx-7 oil coolers are some of the largest factory oil coolers. Avoid the 84/85 coolers as they like to crack at the fitting boss. Go with an FC turbo II cooler. Mazdatrix in California sells them. Not cheap, but one hell of a oil cooler. And mount in front of the rad so it gets cooler air.

I had been thinking of doing this, have had many FB's.

toofast928

Jake fist thing is to record the temperter of the sump oil.

Make or purchase a oil drain plug tapped for 1/8 and insert the probe. For street use you may not need a cooler.
I have a oil cooler in front of the radiator and thinking of moving it behind the radiator, and a smaller unit. On a 80f day, the oil temps hang around 170-180 and it take 5 miles of driving to get there. I never measured in stop n go traffic, maybe this season. I'm using 20w-50w Royal Purple.

In 30f temps the oil barley got to 150f. I had to drain a-lot of milk shake out of the catch can.

My concern is the oil takes too long to get to a temperature, (I don't have a factory radiator oil cooler). The factory block thermostat allows oil flow when closed Porsche wanted to get the oil to temperature soon a possible.

x98boardwell

I didn't realize these cars run very hot.. is this a common issue with cooling? I haven't owned mine long enough and live in the central valley of CA (similar to vegas but a few degrees cooler).

Does anyone have pictures of their solutions or an RX-7 mounted cooler? There doesn't seem to be much room up there with all the other radiators already taking up space... at least in my 91 S4.

Interested to see what others have done and how big of a problem this really is... or not unless stuck in 100+ temperatures at idle.

Bryan

ptuomov

I think this is the best option. It is not very cost effective, however, if you have to get a new radiator as well.

One alternative to end-tank cooler is this sort of heat exchanger:https://www.google.com/search?q=water+to+oil+cooler Radiator water hose is cut and then the heat exchanger is inserted in the middle.

Before doing a whole lot of expensive custom work, it probably makes sense to get accurate measurements of the oil temperature and the water temperature.

Ducman82

good idea guys. i think what i will do is fab in an oil temp sensor. my Mega squirt has engine temp already, and i can make it monitor oil temp. drain plug adapter/temp sensor the best?

Alan

Agree its a good idea to actually monitor oil temp before you make any decisions.

I had very high oil temps (measured with new sensor tapped into sump - not the drain) before adding in rad side tank cooling after the air/oil. Huge difference, the oil behaviour (hot idle pressure) is much better with better cooling & less risk of rapid oil degradation & additive package breakdown.

The vacuum pump also seemed to help reduce oil temps - I can think of several possible explanations here.

You don't want to take oil cooling too far though I agree. The side tank solution moderates the temperature drop somewhat and the oil thermostat should avoid over aggressive use of the cooler loop.

In a stand alone you probably want some similar effect hence proposal for thermostatic control of the fan assist.

Alan

huskeric

I would agree the singular oil cooler may not be the 'best' solution, but anything that adds surface area to cooling - i.e. another cooler/radiator - will surely add a cooling effect. I can say from experience my 951 noted at least 20 degrees cooler while sitting at an idle, verified by an oil temp gauge. This may also be attributable to this being a turbo application. I was simply suggesting a cost effective means (perhaps $150) for areas to explore.

I also noted a similar effect when I upgraded my smaller Z51 oil cooler on my 2005 Corvette to a larger (perhaps 4X larger) Z06 oil cooler. In the case, just the larger surface area made a 15 degree difference at idle - and, after resting after a long run. just saying..

Yes, the preferred solution is another radiator with side tanks - last I checked, aftermarket radiators run around $800 and up. And also concur with needing a fan source to assist in the cooling.

Rob Edwards

Bryan, your '91 should already have the air-oil cooler mounted under the the radiator, fed by slots in the front spoiler. Agreed that it would be good to monitor actual oil temps , probably the easiest way is one of these modded WRX oil drain plugs and an electric gauge:

http://www.deerfieldprecision.com/ca...c75c0cfc534b28

If you find that oil temps get much above 230-240 when stuck in traffic when it's 100+ out, the cleanest solution is a 2-cooler radiator, and a set of hoses that loop engine to rad, rad to air oil cooler, cooler to engine.

hacker-pschorr

I agree with the post of adding a drain plug tapped for a temp sensor, and see what is really going on. You are just guessing at this point.

They don't and it's not a common issue. The cooling system in a 928 is very well designed and overkill for a street car.

If your 928 is running hot during normal street driving, something is wrong.

dr bob

There was a series of discussions on this a while back, with GB opining that he liked having the in-radiator cooler in the loop for situations where there was high recent load and currently no airflow. So hard romp on the freeway, then sitting at a traffic light at the bottom of the exit ramp. His thoughts were targeted towards the later S4 and GTS cars with the oil cooler than dangles exposed under the chin area. The combination of oil-to-air and oil-to-water coolers would have some cooling even whan the car is sitting still.

Quick comment to Rob's post above, I'd be tempted to put the oil-to-air exchanger first in the oil loop, then pass through the oil-to-water exchanger on the way back to the block. That would let the external cooler do as much as it can before sharing heat with the coolant. It would also allow the oil to heat up faster with heat shared from the coolant in colder weather.

Alan

Agreed on the preferred serial config: air/oil -> water/oil

The cooler loop doesn't circulate much oil (almost none) when cold due to the oil thermostat so it doesn't really assist oil warm up very much...

On the later cars the scenario is exactly as described - long high speed freeway run - then you hit rush hour city traffic and grind to a crawl - very common. Late model cars with only an air/oil cooler loose almost all oil cooling. Massive residual engine heat spikes the oil temperatures and pressures rapidly drop to warning levels. Many here have experienced this, the switch to air/oil only was just a mistake.

No fun to be stuck nose to tail in traffic with the "OIL PRESSURE INSUFFICIENT" warning.. I really don't recommend it.

Yes it likely only really exhibits badly in hot climates - but at 120F ambient in Phoenix its not hard at all to achieve (daily!) - Porsche didn't test the design margin on this well enough - more late model inattention to detail as the focus was shifting elsewhere is my guess.

Alan

Speedtoys

The setrab FB cooler you listed is pretty potent, used to cool fluids out of direct airflow in racing apps, a lot.

Comes with it's own fan, and more importantly, shroud too.