I saw a post somewhere that someone "solved" their pressure drop issue by over-filling their oil by 1 quart for track use. Presumably they drained off the over-fill for the street.

I'm curious as to your thoughts on that idea? (and anyone else who'd like to chime in, feel free)

Last month at VIR, I was running Mobil 10w30, I was seeing oil psi in the mid 50's in the 230*-240* range. Closer to 250*, pressure was dropping to the 40's.

So, I'm seeing a rough trend of a 10psi drop per 10* temperature increase. If the trend continues, at 260* the psi is in the 30's. At 270* the redline pressure could be in the 20's, etc. Combine that with loss of pressure in right hand turns and you could have a problem.

I would like to not need a cooler but my gut is saying something different. I'm open to any solid data that says my gut is wrong.

Saw that as well, but IMO inconclusive. FWIW I've been running +1/2-quart overfilled this season as a hedge, but... @BRZ900 added half a quart beyond full and it made little/no difference to the pressure drops they were getting during right-handers. Also, a couple of rounds of baffle designs didn't help either. Accusump appears to be the only proven solution.

Assuming 55psi at 235F, and 48psi at 248F. 12.7% drop in pressure with +13F indicated oil temp, call it 10% per 10F.

Pressure will not drop off linearly with temperature. It'll be more like 10%/10F. At that rate, I calculate ~40psi at 275F (55psi @ 235F * 0.9^3 = 40psi). This isn't going to be exactly right either, but a lot closer than assuming linear decrease in pressure.

I researched this pretty heavily when I bought my '17. Looking at failures I was kind of amazed at how many engine failures were cars with oil coolers. Near as I could tell there was *zero* correlation between failures and whether the car had an oil cooler or not.

This info, combined with tracking the car and seeing oil temp always stabilize just below 275F and never continuing to rise, and knowledge that good synthetic oils are good for over 300F *sump* temps, I decided I didn't need one.

Anyway here's some data (link to thread: https://www.ft86club.com/forums/showthread.php?t=91820 ) to show how much pressure you get going from 20wt to 30wt with no cooler at ~275F (blue and yellow) , and then what happens with a cooler at 250F (green). Note that pressure is about *the same* with 30wt oil either without the cooler at 275F, or *with* oil cooler at 250F. I.e. the pressure drop due to this cooler totally offsets whatever pressure gain there should have been due to the oil running thicker at lower temp.

Answering the thread title, yes, "need" for an oil cooler for these cars is massively overstated/overblown. I'd go beyond that even and say that they more often cause problems than solve any. My 0.02!

I am with you on this @blsfrs. Running a cooler and keeping the oil pressure high just makes sense. Only a few people on this forum say not to run a cooler....

The best you can do is get your own data and do what gives you piece of mind. Which from what I can tell you're already doing.

What works for some people doesn't work for others. Like you I got myself an oil pressure setup and so far at cooler temps it seems fine. If I see pressure under say 45/40 at higher temps I am going to get a proper cooler(running a oem setup at the moment)

Anyway do you :thumbsup:

It is no prob to simply run higher-viscosity oil if you're worried about oil pressure drop due to temp.

That said, we do have evidence (see above post) that an oil cooler itself can have enough pressure drop that there is zero benefit as far as "higher pressure". Hotter 5w30 oil at 275F without an oil cooler is at about the same pressure as 5w30 oil at 250F with an oil cooler.

My advice: don't bother with an oil cooler, these cars at stock power output just don't need them, and they add failure points. Engines *have been lost* due to leaky plumbing of aftermarket oil coolers! Also you are adding a fire risk. It's just not worth it when oil temps are *well* within reasonable range for good synthetic.

Thank you for the links.

I guess it gets down to one's comfort level.

At redline, am I comfortable at 270* and oil psi in the 30's? Or, do I want to risk the down sides of a cooler and maintain 230* and 50 psi?

Or do you want to run appropriate weight oil for the type of driving you’re doing?

This is what I'm comfortable with for oil pressure:
Oil Temp: 176*F
Idle Pressure: 7.3psi or more
6000 rpm: 73psi or more

I assume that the Subaru engineers are aware that oil pressure drops as temps rise, and have spec'd the oil system appropriately.

We know a good synthetic oil can withstand higher then 300*F sump temperatures. Oil pressure is not what prevents metal on metal contact in bearings, oil shear performs that job.

Personally, I overfill .5-1 qt and maintain oil temps below about 270. However, the 270 limit is mostly because if oil temps are getting that hot, there are a million other parts on the car that are also getting very very hot, and I'm trying to protect the entire car, ESPECIALLY the components whose temperature I do not know.

I'd stop trying to fix a problem that doesn't exist.

THIS

Can you clarify a couple of things?

Did you mean 276*? What oil are you running?

And, at that temperature you have 73 psi at 6k rpm? Where is your sensor reading and is it reading correctly?

From what you guys say, high temp and lower pressure will work, but is it optimal?

Those are the factory service manual specifications, so it is 176*F.

I don't know what "optimal" oil temperature and pressure is. I only know what the factory engineers designed for mixed with 20 years of motorsports experience of what "works". That's all I need to stay on track with a reliable machine.

1. I'm pretty sure that temperature is not so good for oil or the engine.
2. I'm pretty sure that I don't want to keep changing my oil for rare track events.
3. I'm pretty sure that we don't have a scientific data sample.
4. I'm pretty sure that on a 100+ degree day at the track, especially with e85, the car can use every bit of cooling it can get. Those on asphalt temps are going to be even higher. With an oil cooler, even on 5-30, I'm not worried because I can get the heat out.

Does the JDM car have a different oiling system than the USDM model?