High oil temps question regarding the Racing Beat 200F recommendation
 

Is it the actual temperature itself that damages the rotors/irons/bearings engine/warps stuff? Or is it the breakdown of the oil that is the real concern?

If a synthetic oil is utilized such as Redline, Mobile 1 etc, what exactly is the downside to high oil temperatures so long as its within the recommended threashold for said oils?

Reason I ask,

RB recommends 200F. However, my engines have regularly seen over 220F. I've seen it even creep up to 230F on the last dyno session when running high RPM for long periods. Water temps are always under 200F.

Traditional oil breaks down at 240f-250f so its obvious why we'd aim for temps under this value. But with an oil that can sustain 300F in racing environments whats the risk of pushing beyond 250F on the track if water temps and IAT are in check?

My buddy says their shop runs the corvette racecars up to 300F regularly with no issues, they start cool down laps around 285F on redline synthetic.

Funny thing - I theorized about this on another forum too. I spent a couple years working in the R&D department of a bearing manufacturer (bigger than our bearings by far) and the temp requirements for rotaries on the face of it make no sense.

What I'm pretty sure the issue is the bearings themselves. See, babbitt starts getting softer in the 300F range (it varies but around there) and past that gets into real risk of melting or failing from oil pressure pushing it out of the way. Well, yeah the oil is cooler than that, but the rotor, subjected to combustion heat, has the bearing press fit into it. So the way I'm figuring, the oil has to be cool enough and have enough flow (via pressure, because on the face of it our oil pressure requirements don't make sense either) to keep the bearing cooled off.

The other thing is that with all the coolers in the system, the "traditional" rotary oil temperature location is right before the oil goes into the block, and the normal location from most other stuff I've seen is in the oil pan, before the coolers. So not quite equivalent there either.

Rotaries rely on oil for cooling more than piston engines, and as noted most people take oil temp before it goes into the engine.

Zach, what oil are you running on your beast?

If it's not Idemitsu 20w50 you're doing it wrong ;)

Cooler oil makes for a much happier engine. An old racer pointed out that hot rotors reflect the heat into the air during the intake cycle which hurts VE. I have noticed that when oil temperatures get over 180F in the oil pan, performance starts to noticably degrade, and this is in an N/A application. In a turbo application, you're just asking for detonation with hot oil.

This is kinda why there is no point to using synthetics in a rotary. You don't gain anything from the temperature resistance benefits because the engine itself doesn't like high oil temps.

I am somewhat surprised that more people don't put thermal coatings on the rotor faces.

How does higher temps affect springs?
Side seals and corners in particular? I imagine they would flatten over prolonged high oil temp.

we asked Jim about this (RIP! he was an extremely nice guy), and he said something about Delta T, and then something about margins. the way i understood it, is that the hotter the oil going in is, the less heat it can remove from the engine.

i'm not sure it has much to do with the oil, although its possible.

you also have to keep in mind that his back ground is road racing, so he needed something that could handle full throttle for up to 24 hours. so a street car could be less strict, as its only going to see WOT for those 12 seconds or less

That actually sounds like the same sort of thing I was theorizing (he says, patting himself on the back) which is reassuring to hear. It would be interesting to try to analyze the effects on power that peejay was talking about - more impetus to work on my engine dyno, I guess.

Oil temps in endurance racing in general can get up to 270 F without any problems specifically mentioned by the Corvette team. I've personally seen my stock 6-port get up to 230-240 fairly regularly as measured at the oil filter so the oil itself can take the heat. I was running Castrol GTX 10w-40. This didn't concern me since I knew I was at stock power levels (except for RB true dual full exhaust) and naturally aspirated. However, now that I have a full bridge 4-port and the car is moving to full time track car duty, I will be installing a second oil cooler in parallel since obviously more power = more heat rejection. Turbo cars are a whole other story that I honestly don't have a lot of experience with yet so I don't even want to speculate what safe oil temps would be. But I'm assuming water and/or meth injection is the best way to hedge your bet if you don't want to invest in more oil cooling.

Cool discussion guys

So, on this engine, I'm measuring the oil temp directly out of the front of the engine, before it passes through the coolers. I'm seeing around 185-195 cruising on interstate, and up to 220-230 slow moving traffic. If I'm stopped for more than 15 mins in stop / go, it will hit 240 (max I've seen).

Now, under load, it pops up much quicker. If we are doing high rpm stuff, just cruising through gears (haven't gone WOT or boost yet), but it will sit around 210-215F.


So where do you guys recommend measuring temp for interpretation. I'm pretty certain there would be a huge drop in temp post cooler, before it goes into the engine. Should I move the sensor?

Just installed 2x oil cooler fans to see if it helps.

I just don't see these engines running much under 220f on a racetrack it seems nearly impossible unless you have some huge cooling hardware

It seems so mixed opinions. Talked with some other big engine builders/racer with this engine who have seen up to 265F and doesn't seemed too concerned. He says he just changes the oil if there's been some decent time over 250.

FWIW water temps have yet to creep over 205F

Definitely would prefer to know the temp of the oil going into the engine. I have read no more than 190-200 going into the engine and no more than 250 in the pan, on Mazda's tech tips.

Measuring at the oil pump outlet is giving you pan temperature plus the heat generated by the oil pump. I have no info on how much temperature is added by the Mazda pump, but up to half of the heat in the oil in an SBC comes from its oil pump...

Yeah I would think pan temperature would be more relevant than post pump. Pan temp and filter temp to see both sides of the equation would be a good start I would say. Very interesting info there about temp post pump Peejay. I would not have thought it would be that significant.

If I understand things correctly, I prefer to know the hottest temps coming out of the engine before it goes to the coolers. If the temps there are higher than I'd like, then I might also want to know the cool temps as the cooled oil goes back into the engine so I know the delta which would give me an idea whether the oil cooling system is sufficient.

I don't see why oil would be any different than monitoring water cooling temps.

mazzei,

about my experience with temps:

i have done a lot of tracking (on 2-rotor cars only, of course) and when measuring the oil temp from the oil filter pedestal (post-coolers) with two mocal coolers and nicely formed ducts i would see no more than 205*F on a 95*F ambient track day (hell-hot ambient temp) high rpm full throttle full boost mostly high RPM.
with a single stock cooler on my white car i would see 240*F on even a cool track day, and i would have to take a cool down lap every two laps. i have a personal limit of 240*F on this one, because as others have said, the rotors are filled with oil and they do a huge amount of the cooling along with the antifreeze/water... i think the different good-decent full synthetic oils start breaking down around 300*F, but rotaries are of course a little more sensitive by design, so i shut it down at 240*F. 250 might be OK for low boost or NA cars, but i think (total guess) oil isnt doing much "pulling away" of the heat from the combustion, so pre-ignition is more likely to happen.

i'm now measuring the oil temp in the oil pan (via 1/8npt tapped drain plug) with dual coolers and effective ducts, and i have yet to see over 190*F oil temps doing repeated 3rd and 4th gear pulls (over the course of ~5mi on the interstate).

i've actually had slight issues with the twin stock coolers OVERCOOLING, even though they have a 180*F thermostat bypass built into each cooler from the factory. cruising on the interstate on a cold day recently (~30*F ambient temp) the oil temp got down to 125*F.



about friends and others' (track veterans) setups:

my good friend (former roommate) has a c5 z06, and nearly all of the corvette guys track their cars and run the oil temp up to 300*F. it is crazy.



my input on your setup and temps:

if your oil is getting that hot at almost zero load, even in stop-and-go traffic, you have a cooling issue.

but i was just thinking; isn't your engine dry sump? how much oil is in the reservoir? that could make a huge difference...

My .02 based on my own experience is it is the result of high temps allowing metal to metal contact. I am not a professional by any means nor qualified so I apologize if I am using any terms incorrectly. If there is anything that I say is incorrect, please feel free to tell me.

Edit: All Temps Taken at the Oil Pan


There was a study that I read awhile ago regarding a test that was done between many different oil brands and weights. Showing Film Strength and Viscosity VS. Heat
Ironically Penzoil came out on top with the highest film strength based on I believe temps of 180* to 220* is what was measured. I am very loosely recalling this info as im having a hard time finding that page. (Will post link once I do, may have been a SAE paper)

Short version is that the oil that I use Castrol 20W-50 maintains 20w properties at operating temp of ~180*, once over 200-220* it drops to 11W or 12W. The same situation with 10W-30 puts the 10W to 5W or lower at higher temps. Obviously after learning that, I began to take oil temps very seriously. I experienced my first "failure" due to high oil temps shortly after where they reached over 250*. Luckily the only thing damaged was my turbo. The hot oil allowed contact on the trust collar/washer and wear to the journal bearings. This caused shaft play and resulted in my compressor wheel making contact with the compressor housing.

I track my car pretty heavily and using dual 19 Row Mishimoto Oil Coolers with a 180* thermostat and I still see temps creep past 220* peaking 240* on the track. This is on a short .5mile track running back to back high rpm. I have been running this engine for the past 2 years, and plan on opening it up in the next few weeks.

I am highly considering moving to dual 25 or 30 row coolers with puller fans.
I use my car for drifting which may not count as a "sport" or "track car" to some of you lol; but I am curious what some of you veteran track guys do for oil cooling when hot lapping or for endurance races. Is the 19 row just too small? This is all with ducting in mind as well.

I apologize if I was not entirely on topic but I did not want to start another thread on a similiar topic.


https://cimg0.ibsrv.net/gimg/www.rx7...aaf21a96c3.jpg

You don't have any puller fans on the back sides of the oil coolers? I bet that would completely fix your problems. I believe the sideways angle of attack and on average lower speed of drifting is not allowing enough flow through your oil coolers. Are you running the coolers in series or in parallel?

I am running my coolers in series. I took alot of time going back and forth between the two. My conclusion was that it seemed that each have their trade offs regarding pressure drops, cooling, etc.

I figured if all things equal; I.E Both ducted properly I should not have any issues. I am currently not running fans. However that it simply due to that fact of limited space behind the oil coolers. I have tried to mount one of the Setrab puller fans to the back however the headlight motor is in the way.

The only way to make it possible would be to increase the angle of the oil coolers bringing the outer side in more like this ( \ ----- / ) as opposed to running it like { _ ----- _ )
I am seeing more and more cars running 25 & 30 row coolers as opposed to these 19 rows.

Im considering replacing these with 2 larger cores and doing away with the headlight motors to allow space for a fan.

Great thread this has become. Thanks guys, I really like this discussion.


So more info on my setup.

The temps usually sit for a good while around 185-190f for a good while, if you're just idling. But after coolant temps creep up to 200F in traffic, the oil always leads it by about 20F moving up to 220f. And if you just sit there, no moving, or moving slowly, they continue to creep to around 230-235F. This is like a good 30 mins sitting in stop and go though. Remember, this car idles at 2300rpm, that likely makes a huge difference.

Now, if you're moving at 40mph+, temps usually will not exceed 210F. On the interstate running 60+mph, after 10 mins or so, temps will drop all the way down to 175-180F. You can take her up to 10k, 100x in a row and temps won't budge over 190F if you're moving 70mph.


So this tells me is mostly an airflow thing, which is why I've added the 2x fans. Hopefully this should do the trick. But ya know, with 2x extra rotors, everything is going to be a damn good bit hotter. Really really want to try e85. Has anyone made the switch and noticed a decrease in oil temps? I've got the flex sensor, but haven't ran the fuel yet!

The car is not dry sump. There's a wetsump pan, the internal pump is used for scavenging and the external pump is used to feed the engine. The internal pump feeds the oil coolers, out of the front cover as usual on fd3s. The external pump picks up from the cooler. The temp reading is literally right out of the front cover, so definitely could be 20+F elevated vs pedestal. I'm definitely going to change the position.


But anyhow, the car see's around 85psi at idle, around 125psi at 5k-7k, and drops slightly to around 120-115psi through out 7-10k to give you guys an idea of oil pressure. It was originally setup by the engine builder with only 90psi, but I shimmed the regulator and bumped up the external pump to help the bearings more at high rpm as recommended by another rotary expert in Miami.

Anyhow, so you guy's think pedestal temp would be best way to go eh?

I notice the same thing, when it gets over 220F the oil pressure comes down a tad bit

Do you know of a thicker oil at temp?

What about if we ran straight 50 weight oil or a 60 weight? 787b builder mentioned using a straight 50 weight, as it doesn't aerate as much at high rpm as the hot/cold weight stuff. However I don't know if bearings require special clearance for that?

For what it's worth, I don't know how accurate the IR gun is but:

When my oil temp gauge reads 200f, the IR gauge shows around 200F on the front cover fitting. But if I shine it on the fitting going into the pedestal, it reads about 180F. 20 degree's lower.

Not sure how accurate IR gun is at oil fittings, vs what is actually running through the fittings

If your at speed temps are under 200, i wouldn't worry about slow moving temps (unless that's the only kind of driving you do). Just make sure your water temps are in line (i.e. the radiator fans are coming on)

:icon_tup: Thanks Tom

My main concern is:

Drove the car to atlanta and back. Got stuck in roadwork traffic and temps were hitting 235-238F oil temp, and water at 205F. Maybe its not so bad to have high temps when youre just low rpm no load?

Good to hear though that guys are reaching 220-240f on racetrack no issue. That tells us the racing beat rule is a little exaggerated

I would be concerned with at speed temps (i.e. with air flowing over the coolers) over 230. That's about where I blew my cooling seals. Idling or at low speed you are not getting any air through the coolers but you are low load and the radiator with fans picks up more of the heat transfer

If you are doing a lot of stop and go driving you could attach oil cooler fans, but I think that mode of transport is better suited for a Prius than a 26B 😉

And to clarify I'm talking about temps going into the engine, not at the sump

I've done thermal development at the OEM level on piston engines. Usually Stock ECUs don't start cutting power until 270F/130C in the sump, and usually full limp mode by 140C which is around 285F. These are on engines with piston oil squirters, just like a rotary. They rely on the knock control system to pull timing at these temperatures, if the spark maps don't already pull enough timing.

What we would do to determine the need for an oil cooler is run it on the engine dyno continuously at a point representing governed max vehicle speed, or most severe towing condition. If it could hit that speed and load continuously without exceeding 130C oil we would cost save the cooler for that vehicle application. So like your family sedan doesn't get it, but the rugged SUV does.

The 270F/130C number comes from the material properties of aluminum. It's sort of a well known rule of thumb, you see engineering consultants recommending this.