oil weight, oil pressure and oil coolers

[Sirbrillo]

I have a 2013 Scion FR-S which I drive mostly as a daily but I intend to use for auto-x and HPDE upon occasion. The car takes 0W-20 stock from the factory, and as they cars run hot (and I live in Houston) I use both amsoil 0W-20 and a 13 row custom setrab oil cooler (thermostatically controlled).

I'm installing an oil pressure gauge to get a sense of my pressures with the oil at full operating temps (212) prior to hitting the track. There has been some concern on the FRS Forum at very high RPMs (7,000+) that oil pressure with a cooler is not sufficient (some owners have seen pressure readings in the low 60 PSI range) under "racing" conditions (high oil temps 250+). As a result, several FRS drivers who track regularly have stepped up to 0W-30 to "raise" oil pressure in these conditions. There is some concern also that the oil coolers create an additional pressure drop exacerbating the issue.

I'm not clear if I really need to run a heavier weight oil to attend HPDE events based on my research on this forum (I've read through all the oil 101 posts).

How do I take my oil pressure readings at 212f at various RPMs and extrapolate if my pressure will be sufficient at higher oil temps (250f+)? From my research, a 30 weight oil shouldn't be materially more viscous at temps in excess of 250f. In addition, while running an cooler does provide a small loss in pressure, shouldn't it be made up by the fact that the oil is cooler and therefore thicker?

I appreciate thoughts and feedback on the situation. I'm waiting on some additional parts to come in prior to testing my oil pressures which I hope to have this week.

 

[d00df00d]

It's hard to extrapolate AFAIK. Testing should be the alpha and omega.

Theoretically, in a completely sealed and ideally rigid system, adding an oil cooler shouldn't cause a significant pressure drop all else equal. And of course, as you noted, all else is not equal because the oil cooler will reduce temps and thus increase viscosity.

Regarding viscosity differences between xw-20 and xw-30: what's crucial here is not kinematic viscosity, but HTHS viscosity. Most good 0w-30s have much higher HTHS viscosities than virtually any 0w-20 (I only know of one exception and it's relatively obscure).

Your car is supposed to be able to hit the track all day with the stock oil. An oil cooler should be all the safety margin you need. If your testing proves me wrong, please tell me ASAP.

 

[Sirbrillo]

I've been told that Subi recommends a heavier weight oil for track duty but I've yet to see definitive confirmation of that.

 

[Trav]

Toyota specs 5w30 as an alternative for the GT86 2.0 (4U-GSE 147kW) in Germany. The high speed conditions there are probably closer to what your engine is being subjected too.

I cant find any documentation from Toyota on track use i have doubts about "Your car is supposed to be able to hit the track all day with the stock oil.".
I would like to see documentation before i accepted that as fact because this is a Suburu boxer and they tend to like thicker oils when tracked.

 

[Sirbrillo]

I'm also open to suggestions for a accurate electronic oil pressure guage that is less than $100. The mechanical one i'm using is ok for testing but I don't want it mounted in the car.

 

[A_Harman]

An oil cooler will undboubtedly add restriction to an oil system, but whether the pressure drop is 0.5 psi (insignificant) or 5 psi (significant) is impossible to know without testing. As long as the oil pressure is staying in the low 60 psi range as you say other owners are reporting, the engine should be OK. 70+ psi oil pressures are not required to keep a film of oil in the engine bearings. In my experience with engines I have worked on, I don't care if oil pressure is 40 or 60 psi, as long as there is enough flow through the bearings to keep them cool during all operating conditions.

Don't be worried about oil temperatures above 212 F, 250+ F oil temperatures are perfectly fine for race applications. Once the oil temperature gets over 300F, it's time to worry.

Overall, I agree with your assumption that the the oil cooler will increase the viscosity of the oil going into the engine because of lower oil temperature. But I won't try to guess if it will cause a net increase in oil pressure due to the lower engine flow demand offsetting the inherent pressure drop in the cooler. There are just too many unkowns.

If you were taking a stock FR-S out to a track day, I would recommend putting in a 5w30 just to be safe. But since you have already put an oil cooler on the car, AMSoil 0w20 may be OK. The important thing is to monitor the oil temperature and remember the max temp that is reached in a lapping session. Then you can calculate the operational viscosity of the oil by using the following link:
http://widman.biz/English/Calculators/Operational.html
Why engage in guesswork when you can know?

 

[Sirbrillo]

In no way trying to engage in guess work, problem is that I won't really know how hot the the temps will be until I get the car out on the track with the cooler. As a relative novice, I'm not going to be balls out 10/10ths out there so I'm guessing based on the outside temps here in Nov and other FRS owners oil temps observations with a cooler that I'm going to have temps in the 240-250ish range by the end of the day.

I have no issue running a 0W-30, but didn't want to waste the oil I just replaced (amsoil 0W-20) in less than two months if there is a way I could know ahead of time that my current setup will work.

is there a reason you recommended 5w-30 over 0w-30?

 

[SteveSRT8]

^^^Fewer viscosity issues with less additives to depend on. 5w-30 is more stable.

You will need to know both oil pressure and oil temp simultaneously to see what's up. I have run many track days at 300 degrees temp on M1 0w-40 and had great UOA's. Good synthetic is not harmed by that temp automatically.

There must be some track rats running this car hard and reporting their exploits. I would check with them. Don't be too quick to add thicker oil until you're sure you need it.

 

[Sirbrillo]

Thanks I didn't realize 5w-30 was more stable than 0w-30.

 

[y_p_w]

Originally Posted By: Trav
Toyota specs 5w30 as an alternative for the GT86 2.0 (4U-GSE 147kW) in Germany. The high speed conditions there are probably closer to what your engine is being subjected too.

I cant find any documentation from Toyota on track use i have doubts about "Your car is supposed to be able to hit the track all day with the stock oil.".
I would like to see documentation before i accepted that as fact because this is a Suburu boxer and they tend to like thicker oils when tracked.


More than likely they would have warranty terms that state that track, racing, or competition use could negatively affect warranty coverage.

 

[Sirbrillo]

STi and TRD would still have formal recommendations for race teams on the correct oil weight irrespective of warranty issues.

 

[GutsyGecko]

Don't worry about it. 60 psi at 250F is a rediculous amount of oil flow. I have managed to get my oil to just shy of 300F, with a 50wt oil, turning 6000 rpm for minutes at a time. My engine still runs.

 

[Sirbrillo]

Originally Posted By: GutsyGecko
Don't worry about it. 60 psi at 250F is a rediculous amount of oil flow. I have managed to get my oil to just shy of 300F, with a 50wt oil, turning 6000 rpm for minutes at a time. My engine still runs.


The guy on our forums that prompted me to think about the issue was concerned that low 60's PSI at 7,200RPM violated the 10 psi per 1,000 rpm rule. The FR-S engine manual calls for ~73PSI at 6,000 RPM at 176 degrees f. Per his testing he was above 70psi until he hit ~7,000 rpm and then it started dropping down to ~62psi at redline (7,400rpm). He was running a fairly big intercooler (19 row vs. my 13). After rereading his post i don't think he was tracking the car at the time he tested his pressures which has me more concerned as viscosity would fall even lower as the oil heats up.

 

[GutsyGecko]

Sounds to me like you will be flying blind until you bite the bullet and install oil temp/pressure gauges first. Pressure being the most important. Either that, or just drop in a 0w-30 and sleep well at night. I'm not claiming to know more than the engineers, but I'm having a hard time seeing how an oil cooler is causing pressure to drop that much. I mean its apples to oranges, but my cooler is literally almost the size of a large radiator and I've successfully run thin 30wt, almost borderline 20wt, in an engine that specs 40wt minimum. The problem is that oil pressures are not linear with regards to heat. Also, I hope you chose a plate and fin style cooler, the tube coolers are not very durable, and would have me sweating bullets used for oil.

 

[SteveSRT8]

Originally Posted By: Sirbrillo
He was running a fairly big intercooler (19 row vs. my 13). After rereading his post i don't think he was tracking the car at the time he tested his pressures which has me more concerned as viscosity would fall even lower as the oil heats up.


Did you mean oil cooler? If you're running boost then all bets are off!

 

[Sirbrillo]

Originally Posted By: SteveSRT8
Originally Posted By: Sirbrillo
He was running a fairly big intercooler (19 row vs. my 13). After rereading his post i don't think he was tracking the car at the time he tested his pressures which has me more concerned as viscosity would fall even lower as the oil heats up.


Did you mean oil cooler? If you're running boost then all bets are off!
.

I meant oil cooler, apologies.

 

[Sirbrillo]

Originally Posted By: GutsyGecko
Sounds to me like you will be flying blind until you bite the bullet and install oil temp/pressure gauges first. Pressure being the most important. Either that, or just drop in a 0w-30 and sleep well at night. I'm not claiming to know more than the engineers, but I'm having a hard time seeing how an oil cooler is causing pressure to drop that much. I mean its apples to oranges, but my cooler is literally almost the size of a large radiator and I've successfully run thin 30wt, almost borderline 20wt, in an engine that specs 40wt minimum. The problem is that oil pressures are not linear with regards to heat. Also, I hope you chose a plate and fin style cooler, the tube coolers are not very durable, and would have me sweating bullets used for oil.


its a setrab 13 row oil cooler so it should be durable.