oil cooler fittings / dual oil coolers??
 

Question One:

How much should the banjo fittings on an oil cooler be torqued down? My oil cooler was leaking around the fitting so I swapped it out with another one. Got it so the leak was essentially gone. It's been a few days and I have had no problems...until now. I just looked underneath my car after I noticed a interesting "oil on hot metal surface" smell and, lo and behold, it's leaking again. What is the deal? Did I not torque the fittings down enough?

Question Two:

What's this I've been hearing about running two oil coolers in tandem? I have heard a few rotary fools mentioning this...not on this forum though. Is it legit? Can you do it and is there any good thing about it?

first, are you sure it is the fitting that is leaking? the oil coolers can develop cracks on the corners of the cooler where the fittings sit and can be misleading.

second, i don't know why they use dual oil coolers, seems like overkill to me. the coolers do not flow 100% of the time anyways. there may be some benefit to keeping your oil cooler than normal but there is also drawbacks, unless like i said they are doing some serious power output and need the added cooling to keep the oil from overheating. none of which should be of concern unless you are doing some serious mods for power output.

I think that my first oil cooler had a cracked weld. That's why I snagged another one. But i'm still not sure why it's leaking. I'll see about getting it pressure tested...

did you replace the copper washers with new ones? also check the banjo bolt for any burrs or something that could cause it to seat improperly and lastly check the seat at the oil cooler. be sure to install new copper sealing rings if you haven't.

I replaced the copper washers. I have an extra set of banjo bolts if I need em. Thanks forr the info man....I appreciate it!

-Nader

np and good luck, i think that is all we can suggest unless it is your cooler line causing it not the cooler or fitting, i know the cooler lines tend to leak a little before they 'pop'. :)

Oil temps can get really high on 7's, much higher than the water temps, buy adding another oil cooler, you can drastically reduce the oil temps and thus reduce the chance of oil viscosity breakdown and engine failure.

Its more noticed on turbo cars where the oil is run through the turbo to both lube the bearings and cool the turbo. Stock RX-7's also have coolant run through the turbo to aid in lkeeping it from melting down. Turbo Cars will thus see higher oil temps than non torubo's

Some third gens came with dual oil coolers for this exact reason ( I think the R1's)

I have another cooler lying around, I may be running duals myself in the spring.

40-50 ft-lb as per the FSM.

The FC has probably the best oil cooler ever fitted as stock. Even the FD R1's two small oil coolers are regarded as inferior. High-powered turbo'd FC's rarely have oil temp problems unless they're on the track where full load is used for much longer.

Unless you actually have a measured oil temp problem (that isn't caused by defective equipment), don't waste your time and money on a second oil cooler.

running 2 oil coolers solved my problem with overheating oil....it was overheating on highway, not even close to race conditions.....

both serial and parallel setup works

I think its a fantastic idea... I moved my oil cooler to the front and it kinda sits above my Spearco 27x8x4/FMIC.. I have a Bomex bumper with the slit in front, so I carved out the support bumper so air would make it past that and the oil cooler sits right behind that. works really good and the radiator gets better flow too. just an idea. anyone else?

Careful who your calling a rotary fool as some of our names differ from site to site.

I wouldn't do a serial setup, the pressure drops are to extreme to the point it will either open the bypass inside the oil coolers which results in no oil cooling, or have half the oil blowing out the relief in the front cover which jsut heats the oil and foams it..... I currently have a pressure guages either side of the oil cooler since I removed the internal temp and pressure bypass, there is nearly a 60 psi drop across the oil cooler, and yes mine is clean...Shimming the rear oil pressure regulator does nothing to solve pressure drop in the oil coolers, you can shim the front, but at the risk of either shearing the shaft on the oil pump, breaking a gear inside the oil pump, or blowing out the front cover o-ring, since you would have to have nearly 195 psi pre oil cooler to maintain 75 psi at the engine...I have a engine here apart that has a broken oil pump gear, the front regulator was seized in the front cover, it originally looked like a front cover o ring falure , but it wasn't.. I agree with NZ, one oil cooler is enough, I relocated mine and ducted it , it actually sits on top of my front mount intercooler... I was unsure of what oil pressure I would end up with changing to 10 an lines, and a non bypass cooler, but with my other oil pressure control modifications, my oil pressure is now 75 psi at idle and 100 psi from 1800 rpm up, and is adjustable up to 145 psi but I am gonna play with the pressure to see how it affects rotor cooling, and oil life...
I don't think its worth playing with the adapters to the metric fittings, another place for a leak and another crush washer to rely on...
I just welded AN fittings directly to the oil cooler and had done with it...

Yeah, but that's because you blocked all the airflow to the original oil cooler. ;)

Max, I almost allways agree with you, but not on this one. I can say this because I have mine in series, and they work great, They do need lots of air flow to work though. Nader, You know I have two coolers, come over if you like, and we can copy my system for you. My set up is one mounted at the top of the radiator, and one at the bottom. My oil temps are ~155-160 while cruising, and ~200 after 1/2 hour on the track. This is with a oil, and water cooled TO4S putting down ~300 to the wheels. It is a great, and a simple mod, you do need to account for any blockage of the radiator, by managing the incoming air, or you will habve problems. I will evntually do a write up, as the benefits are huge. The mod dropped my original oil temps ~40 degrees at the track. It is not however as simple as just installing a second cooler. Regards, Carl.

So you are willing to live with 120 psi pressure drop across the coolers, trust me, series is a mistake, on other coolers like the twin Greddy's and Feed kits, they have alot less pressure drop across the coolers, you have more oil going back into your pan, then you do through your coolers via the bypass, I 'll lay a bet your oil pressure at the engine, is no where near mine.....Max

Just gonna add a few more tidbits here...
Once you increase the pressure drop via dual serial coolers, most likely the front cover bypass is open pretty much all the time in various percentages dependent on engine rpm, once that bypass is open, that oil is doing nil for engine cooling, its not going to pickup any rotor heat at all, in fact its just giving up heat to the oil pan and front cover, if you measure your oil temps at the pan, they are not an accurate measurement, as alot of that oil has not seen the hot parts in the engine with the bypass open.. I have shimmed my front cover bypass and I can see it open now at about 170 psi, stock was around 155.. so lets say with 150 psi you feed the coolers, the coolers have a bypass in them of 50 psi, I know they have around 60 psi of pressure drop across them with 40 weight oils at operating temp , which leads me to beleive for the most part the stock oil pressure thermal bypass is bypassing oil alot of the time around the oil cooler, and most of its effect is just from the thermal mass, once the oil gets Uber hot though the oil pressure drop across the coolers probably drops to below 50 psi and they start doing some real cooling... So at this point, serial coolers with cool oil due to low internal cooling and internal releif bypassing, is most likely going straight through the oil cooler bypass to maintain oil pressure, with no travel through the actual cooler at all...basically its doing a loop through the lines to the motor... Now if you plug the internal bypass, yes you start to get cooling, probably very good cooling, at the expense of flow rate, you double your pressure drop, half your volume, but double your heat transfer rate.. The problem again, most oil is just going pump---->front cover----> pan over and over again...Limited rotor cooling on 300 hp motor might live, but probably not for long on anything more than that, or for any amount of time..
Parrallel would drop the oil cooler velocity internally, and give more heat transfer area, thus increasing cooling while halfing the pressure drop across the stock coolers as the flow rate per oil cooler becomes less... But if you take the stock one, and stop the internal bleeding and get it in the airstream, its alot less plumbing, wieght, and leaks to worry about....Max

Running them is series just makes no sense. It will always result in greater pressure drop and lower flow compared to the original set-up, while running them in parallel will result in less pressure drop and higher flow. As mentioned above the lower velocity through parallel coolers also increases heat transfer. Series may be easier but it certainly not better.

I was thinking of trying the dual coolers the way higgi has his because we have the same fmic and fc2000 kit. And yes it does run to hot on the highway. This is my main concern because I have designed my turbo setup to run down cars from a rolling speed. Not much of a race if I can't run highway plus speeds for long. So I got to get something done.

I am running them in series, with 75-80psi oil pressure regulator i see atleast 30psi at idle (warmed up) and atleast 75 psi above 3000 rpm (warmed up)

My oil temps on highway were hitting 100+ C without boosting. Now i see around 60-70C on highway without boosting and 80C max even when boosting hard. On small drift track, which is almost constant 2nd gear in 5000-8000 rpm range and barely any hardly any flow from front, i am able to get close to 100 C after while, but haven`t got it over yet.

Do what you want, series works fine, and is easier to plumb. No one said it was better, just said it is proven on a serious race car to get the job done as well as anyone posting ANY other oil cooling set-up... Carl

I am measuring temp, and presure at the filter with Autometer mechanical gauges, pressure at full boost/WOT is ~70-80psi, temps after 30 minutes of hardcore road racing ~200, 155 cruising, got a better working system?

Yes I do, I make more oil pressure at idle then you guys do at WOT.....:)...Max

ok....

Obviously theres a major difference of opinion on the matter. Carl, I will call you and swing by your house to check out your setup at some point within the next week if you're home for the holidays. In the mean time, I'll ask Alan at OPAK Racing if I can get a hold of him and I'll also ask Mike at Michael's Mazda Performance.

Thank you all for the mass amounts of information on the oil cooler setup. I'm gonn ahave to read through the posts a few times to soak everything in! :)