Oil cooler
 

Is a oil cooler required ?maybe a stupid question but im gonna ask anyways.

I would certainly advise you to keep an oil cooler on it, rotarys run hot so anything to keep the temps down. but if your in a pinch and its your only car and dont have one, you could do it. most cars dont even have them. but if you do delete it make sure to block off the feed and return.

Your oil cooler is one of the most important parts on a rotary engine car it cools the rotas and keeps oil temp down and water temp lower .Without it your motor would not last long

Yes it is a requirement you have at least one. It's not a suggestion or reccomdation you have one, it's a requirement. It would be cool to see how the temps react without it though.

Everything related to reliability starts with cooling. And IIRC a professional builder once said that about 25% of the cooling on a rotary is done by the oil. Anything you can do to improve that...clean the cooler, straighten fins, add a second, is good. You certainly wouldn’t want to remove it.

Let me try to turn this into a more useful thread (if the mods will permit) rather than starting a new one.

Q: My oil temps are too high; where should I start trouble shooting?

Details:
I just took delivery of a '99 RB (single oil cooler) and noticed that my oil temps get a little too hot for my liking.

Normal operating oil temps are about 90*C (194*F) and when I head up a fairly steep hill for about 10 mins, mostly in 2nd gear but not past 3200rpm, the temps easily get up to 115*C (240*F). The first time I drove it up hill I had the AC on, and I broke 120*C (250 deg F) before realizing it was too hot and turning on the heater instead.
OTOH when I coast downhill with engine drag, I'll only get to 85*C (185*F).

Ambient temp is about 30-35C (high 80s to mid 90s)

The oem dash water temp shows "fine", and the aftermarket gauge that the car came with is broken (am trying to fix it...) so I can't get a good water temp reading.

It looks like my oil pan has a broad dent in it, but not too deep/serious.

Oil pressure generally looks fine, though a little low at idle.

I have the factory fog light option, which is blocking part of the side vent (that feeds air to the oil cooler.)

Any ideas?

Thanks in advance!!

Never monitored oil temps so I can’t say accurately what is hot and what is not. Maybe others can chime in. Regardless you really need to work that coolant temp gauge. Do NOT rely on that Factory temp gauge. It really only tells you when the car is warmed up. By the time it moves to tell you it’s hot, it’s almost always too late.
If the fog lights are in the stock location (edit: on an S6) they don’t affect air flow to the oil cooler(s).
Do you have the Factory under-tray/belly pan in place?

Thanks @Sgtblue - yes, I am aware of the inaccuracy of the stock temp gauge - it's legendary! Today's to-do list is getting the temp gauge back up and working.

This is a 1999 car ("Kouki" or "FD generation 5" or whatever), with the oil coolers in the side vents, and the fog light is also right there, blocking air flow... but I'm not sure this would really be that big of an issue.

AFAI can tell, all the factory plastics are in place... the car was mostly stock when I got it.

I couldn't get the wiring for my temp gauge to work last weekend, so I will be installing a new temp gauge this coming weekend (which also better fits my aesthetic.)

So I've been looking at my oil temps more closely.
Normal operating oil temps are actually more like 95*C (203*F)!
But when I head up a fairly steep hill for about 10 mins, mostly in 2nd and 3rd gear but not revving past 3000rpm, the temps easily get up to 115*C (240*F) or even 120C (248*F)!!!

This is with a warm ambient - around 85-90*F.

When operating temps get to 100C (212*F), even if I pop the hood and prop it open, the temps don't really come down, even after 5-10 mins of idling. Is this normal??

Oil temps are generally OK in the 240F range, although they are high for relatively normal driving that you have mentioned. Coolant temps would be too high at 240F.

You could likely use a set of twin oil coolers to bring them back down to a lower level. The factory single oil coolers are notoriously undersized for any sort of spirited driving.

I saw a drastic drop in oil temps when I upgraded to dual oil coolers (R1), and then again, another drastic drop in oil temps with aftermarket 25-row oil coolers.

Thanks, @Copeland !

Though I know how famous the FDs are for running hot, I just can't believe that 240*F would be "normal"...
I have gone ahead and ordered a pair of 19 row units (I'm worried about ground clearance lol), but am worried that this is just a crutch/bandaid for a more serious problem.

I guess the right question is, "what would cause an FD to structurally/systematically run abnormally hot oil temps?"

Any help would be appreciated!!

It may only abnormal if we're comparing it to a piston engine. Thinking out loud, the stock FD has not one, but two turbochargers. Also oil is sprayed on the "back side" of the rotor for cooling just like it's piston's counterpart. But the rotary's combustion surface area is pretty large for the displacement, and those combustion events occur at a greater frequency.

Agreed. There's also a smaller surface area, which means slower heat dissipation. And 6 ignitions per rotation of the dorito! (2 sparks)

Sorry, I was unclear.

I meant, given the already hotter than normal oil temps, what might cause my car specifically to be running even hotter than other comparable FDs?

I’m not convinced you are running hotter than a comparable FD with a single cooler. Once you’re able to monitor coolant temp that should give an idea of where you’re at overall.

I think the oil temperatures you are seeing are normal for a single oil cooler FD. The problem is that most people are just unaware that the oil temps get that high with the single oil coolers, otherwise they'd be upgrading much faster!

Oil temps and coolant temps are related fairly well; So if oil temps are high, coolant temps will follow and vice versa.


For example on my FD over the years (good condition cooling system, no leaks, 50/50 coolant):

1. (13B stock port, twin turbo) Stock radiator, single oil cooler. 240F+ coolant temps in summer (95F on average) with A/C off and mild spirited driving. Upgraded radiator immediately. (Note: Factory dash coolant temp gauge still did not move from normal position.)
2. (13B stock port, twin turbo) Koyo N-flo radiator, single oil cooler. 230F coolant temps in summer with A/C on and mild spirited driving. Lower temperatures with A/C off by about 15F.
3. (13B stock port, twin turbo) Koyo N-flo radiator, dual factory oil coolers. 195-210F coolant temps in summer with A/C and mild spirited driving.
4. (13B street port, single turbo) Koyo N-flo radiator, dual factory oil coolers. 190F coolant temps in summer with A/C and mild spirited driving.
5. (13B street port, single turbo) Koyo N-flo radiator v-mounted, dual factory oil coolers. No difference with v-mount from above.
6. (13B semi-pport, single turbo) Koyo N-flo radiator v-mounted, dual factory oil coolers. No difference from above.
7. (13B semi-pport, single turbo) Koyo N-flo radiator v-mounted, dual 25-row oil coolers. 176-180F coolant temps (thermostat minimum) with A/C and mild spirited driving.

I have omitted oil temps as I did not always log them along side coolant temperatures. You can still see the relationship between the two.

In addition to twice the capacity to cool you get about 15% more oil capacity with the stock ‘R’ dual coolers.

WOW.
See, here, THIS is a valuable resource!
Thanks for sharing, @Copeland!!
What kind of IC were you running on those? Same throughout? (Not that it would necessarily change the operating temps, I'm just curious about the physical setup of the radiator vis-a-vis the I/C.)

On my 180sx (SR20DET) oil temps would track coolant temps, but would just be about 5 to 10*C higher. I would have expected similar on a 13b, anyway.

It's great to get an idea what kind of difference to expect from the dual oil coolers and an uprated radiator.
Most interesting to me is the lack of difference in mounting the V-mount!

Thanks again!!

My intercooler has changed several times but I never ran anything in front of the radiator, so it wouldn't have affected coolant or oil temps.

My intercoolers have changed as such:
Stock intercooler > Upgraded similar to stock size SMIC > M2 Large SMIC > HKS v-mounted intercooler > Custom A2W intercooler

I'm sure that coolant and oil temperatures will always have a relationship together but they'll vary entirely based on how adequate the cooling solution is for each.

Currently my oil temps float around 160F on the highway with a 180F thermostat and my coolant temps rarely go above 180F on a 180F thermostat. I'd expect an inverse relationship with factory oil coolers.

How was your radiator set up with the HKS? We're the fans sitting too low? Was there any feasible way to alter the radiator position so the fans wouldn't hang so low?
Thanks!

Also, I have seen this "M2" come up from time to time.
Is there a website or can you tell me more about this brand? It seems like they make quality pieces... Thanks!

M2 has been out of business for about 15 years. It’s a good SMIC, possibly the benchmark, just be sure to buy the duct with it. And IIRC M2 large will require battery relocation...or at least reduction.

HKS v-mount information here:
https://www.rx7club.com/3rd-generati...sions-1120967/

Sgtblue is right, you'll have to search the forums to get information for M2.

Someone back in 2003 is saying that M2 closed in 95...!!! Wow. I didn't realize their stuff was that old...
https://www.rx7club.com/showthread.p...1&page=1&pp=15

Great reading.