Is need of external oil cooler overblown

[ZDan]

Originally Posted by blsfrs

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?

You can have oil at 270F *and* oil pressure in the 40s or even 50s if you go to a high enough viscosity.
Look at the chart I posted above. 0w20 at ~275F is ~5.5 psi/krpm (+/-), while 5w30 at same temp is ~7.5 psi/krpm (+/-). Implying that at 6k rpm, 275F, 0w20 is ~33psi and 5w30 is ~45psi. So *without* an oil cooler, 5w30 is running about +12psi higher oil pressure vs 0w20 in the medium/higher rpm range. I.e., going up in viscosity is *very* effective at increasing oil pressure, if that is the metric you are most concerned about.

Meanwhile, the same 5w30 running -25F cooler at 250F, is at about the *same* 7.5 psi/krpm, so still ~45psi at 6000rpm, *zero* increase in oil pressure for the same 5w30 oil running -25F cooler with an oil cooler.

So if oil pressure is what you're deciding to be obsessive over, going up in viscosity is a much more effective way to ensure higher pressures than going with an oil cooler.

Originally Posted by blsfrs

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

All I'm saying is that if you are interested in "higher oil pressure", running higher viscosity oil is definitely for sure going to provide that. While running an oil cooler even with significantly lower oil temps, might not give you as much increase in oil pressure. Benefit of cooler oil is to some degree going to be offset by pressure drop due to the cooler. In this case, pretty much no increase in oil pressure despite significantly cooler oil.

To be taken with a grain of salt of course, but for sure that is what this data suggests.

If I was as worried as you about oil pressure vs. temp, I'd be running 0w40 all track season instead of 5w30.

But it seems to me the most critical thing is that oil is being supplied at all and not necessarily whether that oil is at 275F or 235F. IMO, RTV cloggage and pressure loss due to cornering g's and perhaps basic Subie flat-4 oil passages and tolerances are a thousand times more important.

Oil pressure in the 30s at 275F isn't what kills these engines. Oil pressure in the teens and single-digits due to other issues is. IMO...

[Tokay444]

I run 0w40 year round, in Canadian winters, and on track in Atlanta in the summer. 260,000 trouble free kms.

[autoracer86]

Based on the way Toyota "backs" their warranty for track usage I am not sure I would trust what the engineers deem safe applies to track usage LOL.


Also I recall the Toyota specing 10PSI per 1000 RPM for oil pressure which you're not hitting on track once the temps come up. Do you NEED that much oil pressure heck if I know

[x808drifter]

Originally Posted by autoracer86

Based on the way Toyota "backs" their warranty for track usage I am not sure I would trust what the engineers deem safe applies to track usage LOL.


Also I recall the Toyota specing 10PSI per 1000 RPM for oil pressure which you're not hitting on track once the temps come up. Do you NEED that much oil pressure heck if I know

Then you're misremembering.
That has been a rule of thumb for decades.

[autoracer86]

Originally Posted by x808drifter

Then you're misremembering.
That has been a rule of thumb for decades.

Maybe the 10psi thing is more a generic rule that applies to many cars. So you could be right there.

All I could find from the manual is this. Might not be much help as the temps are so low but mid to low 30s is way off 73psi.

But again I have no clue how bad 30psi is for the motor. Personally for me at this stage and the type of track day format I am running. I just keep an eye on oil temp and pressure and pull off when I feel I need to.

I have no real reason to push an extra few laps when I can just come in and go back out. I could also just do a cool down lap if I like. The session goes well beyond 20 mins.

[ZDan]

Originally Posted by autoracer86

Maybe the 10psi thing is more a generic rule that applies to many cars. So you could be right there.

All I could find from the manual is this. Might not be much help as the temps are so low but mid to low 30s is way off 73psi.

The spec you quote is not meant to imply that you *have* to have 73psi at 6000rpm, it only means that at the specified 176F oil temp the oil pressure should be 73psi at 6000 and if it's lower than that *at that oil temp* it means something might be up...

Are you seeing mid to low 30s at 6000rpm? What viscosity oil are you running?

Ultimately you only need enough oil pressure to keep the bearings fed. Hydrodynamic wedge is what really carries the loads. Could be that 30psi is sufficient. Any case, if you want to see higher pressures at track temps, maybe consider going to higher viscosity.

[autoracer86]

Originally Posted by ZDan

The spec you quote is not meant to imply that you *have* to have 73psi at 6000rpm, it only means that at the specified 176F oil temp the oil pressure should be 73psi at 6000 and if it's lower than that *at that oil temp* it means something might be up...

Are you seeing mid to low 30s at 6000rpm? What viscosity oil are you running?

Ultimately you only need enough oil pressure to keep the bearings fed. Hydrodynamic wedge is what really carries the loads. Could be that 30psi is sufficient. Any case, if you want to see higher pressures at track temps, maybe consider going to higher viscosity.

That makes sense about the specs. Thanks

Yes higher viscosity oil or lower the oil temps. Without doing a deep dive on my data he is what I shared in my build thread from my last track day.

5w-30 for oil weight. Seems like a good happy medium for street and track. UOA has been very good as well for me so I don't see myself changing.

Again keeping temps under 260F is easy enough for me with the OEM cooler but if I was struggling to keep temps down and it caused a pressure drop I would get a better cooler before changing the viscosity. That is just what I preferer. To each their own.

Max Coolant Temp: 194F/90C
Max Oil Temp: 237.2F/114C
Oil Pressure: 34.9PSI - 60.2PSI AVG 52.0
Seeing around 55psi at 7k

[Ultramaroon]

The spec is a single datum point good for a couple reasons. As Dan says, it specifies a reference point for pressure as a function of both temp, and engine speed. I also interpret it as a suggested minimum (normal?) operating temperature. Falls in line with most oil cooler thermostats at 180F.

[NoHaveMSG]

Originally Posted by autoracer86

That makes sense about the specs. Thanks

Yes higher viscosity oil or lower the oil temps. Without doing a deep dive on my data he is what I shared in my build thread from my last track day.

5w-30 for oil weight. Seems like a good happy medium for street and track. UOA has been very good as well for me so I don't see myself changing.

Again keeping temps under 260F is easy enough for me with the OEM cooler but if I was struggling to keep temps down and it caused a pressure drop I would get a better cooler before changing the viscosity. That is just what I preferer. To each their own.

Max Coolant Temp: 194F/90C
Max Oil Temp: 237.2F/114C
Oil Pressure: 34.9PSI - 60.2PSI AVG 52.0
Seeing around 55psi at 7k

For reference, those are about the same number I see with 0-20 Motul 300V though my pressure seems to peak about 5800-6k and drop off a bit after.

[blsfrs]

Originally Posted by Ultramaroon

The spec is a single datum point good for a couple reasons. As Dan says, it specifies a reference point for pressure as a function of both temp, and engine speed. I also interpret it as a suggested minimum (normal?) operating temperature. Falls in line with most oil cooler thermostats at 180F.

Running around town, my oil temp stays around 200*. Some articles say the oil has to get to 212* to boil off moisture in the oil. I'm guessing fuel and other contaminants boil off at lower temperature? How often should we try to get the oil temperature to 212*?

[Ultramaroon]

Originally Posted by blsfrs

Running around town, my oil temp stays around 200*. Some articles say the oil has to get to 212* to boil off moisture in the oil. I'm guessing fuel and other contaminants boil off at lower temperature? How often should we try to get the oil temperature to 212*?

It doesn't need to ever. Just like how your bathroom mirror dries off after taking a shower. The internal environment of the engine is already at a high enough temperature and the crankcase atmosphere is at slightly below ambient pressure. What should be avoided is operation for short periods where the engine never reaches normal operating temp. My oil temp gauge never shows higher than the water temp.

[new2subaru]

Oil pressure gauge is on the Xmas list. I'm curious now.

Been running the JRDOC for years, 40ish track says and no issues.

I run Mobil 0W-40 oil. My coolant temps are around 200ish and oil 235. I can stay out as long as I can handle it and it doesn't change. Seems to be working so far. I also change the oil every 2 outings. Overkill, I know. It's cheap compared to any other consumable and I'm under the car anyways doing a check.

In my mind heat causes wear and keeping things a bit cooler should help. I'm not saying that you have to have a cooler but that's just my thought process.

Knock on wood, another 12-15 tracks days next year.

[autoracer86]

235f oil temp on track is pretty good I would say. Shouldn’t run into pressure issues at that temp.

[new2subaru]

Originally Posted by autoracer86

235f oil temp on track is pretty good I would say. Shouldn’t run into pressure issues at that temp.

I would think so seeing as it hasn't gone BOOM. Great little car