Is need of external oil cooler overblown

[ruturaj001]

I have seen numerous videos saying the car needs an external oil cooler. I am not saying everyone is wrong.

My understanding is, which can certainly be wrong

A good oil (5w30 oil with HTHS of 3.5+) should be able to protect well till 250-270F and a 0w40 beyond that till about 300F. I assume people see even higher temperatures than this and decide to get external oil cooler or few at lower temperatures. Then it seems to create it's own issue like pressure drop (I assume due to added space for oil) and it becomes a new problem where something like accusump is needed. And the whole system gets too complicated. Am I missing something

1. Are pressure drops are bad even on stock setup? Are there any numbers you could share?
2. Is there platform specific issue where oil can not protect engine like it does on European cars for similar temperatures (again probably related to oil pressure)

Just trying to figure out why people start recommending oil cooler at 250°F. Again not saying they are wrong but what am I missing. Feel free to say I am wrong with reasoning if I am.

[EndlessAzure]

This thread is often referenced
https://www.ft86club.com/forums/showthread.php?t=91820

Like you said, concern is not about oil breakdown. Rather, it's about proper pressure, which is an indicator of pumping effectiveness and oil flow.

Pressure curves and data (both as a function of time over a lap and map versus temperature) are out there and especially concentrated in this forum. [ Google: oil pressure site:ft86club.com ]

In the end, it's whatever condition you decide you're comfortable running the engine. Usually the breakover for people's comfort level hits around 260F. In practice, it's not hard at all to reach those kinds of oil temperatures on the track. It's usually not a concern for street driven cars, but it's still easy to raise temperatures to that level on a spirited high-rev drive on a curvy road

Subaru thinks that 73psi (500 kPa) at 6k RPM is nominal for 176F (80C) oil temp; that works out to about 13psi per 1k RPM

[DarkPira7e]

As said be Endless, pressure is what gets scary, there's just a correlation between temp and pressure that can necessitate a cooler

[ZDan]

Yes, hotter oil is thinner, that's why it is appropriate to run run 30- or 40-weight to have appropriate viscosity/thickness for higher oil temps seen while tracking. 5w30 at 275F is about the same viscosity as 0w20 at 250F. No big deal, oil temp "issue" is pretty overblown IMO...

[ruturaj001]

Thanks everyone. I understand high temperatures mean lower viscosity which results in lower pressure.

Oil cooler also reduces pressure at all temperature ranges. At 260°F the oil viscosity is 7.8 and 8.4 approximately for Pennzoil euro L 5w30 and Mobil1 FS 0w40, assuming oil cooler kept temperature at 212°F the viscosity would have been be 12.5 ans 13.8 instead. My question would be which is lower

Oil pressure at 260 without external oil cooler
Oil pressure at 212 with external oil cooler

I understand at say 300°F as highest temperature without oil cooler, it would be better to have oil cooler and lower temperature. And at low temperature it would be worse to have oil cooler, pressure wise. What's the tipping point? 260°F? If so why?

Sorry about lots of questions, just trying to understand and thanks everyone for reply.

[ruturaj001]

Not factoring in the drop on turns because it exists regardless of oil cooler.

[ZDan]

Originally Posted by ruturaj001

Thanks everyone. I understand high temperatures mean lower viscosity which results in lower pressure.

"lower" pressure isn't necessarily a problem, you only need pressure sufficient to keep the bearings fed. In the "working zone", hydrodynamic wedge is what supports the crank in the main bearings and the rods in the crank. HTHS is probably a better number to look at for oils to see how well they do there. Fixation on oil pressure and thinking "more is always better" is IMO somewhat misguided.

Oil cooler also reduces pressure at all temperature ranges. At 260°F the oil viscosity is 7.8 and 8.4 approximately for Pennzoil euro L 5w30 and Mobil1 FS 0w40, assuming oil cooler kept temperature at 212°F the viscosity would have been be 12.5 ans 13.8 instead. My question would be which is lower

Oil pressure at 260 without external oil cooler
Oil pressure at 212 with external oil cooler

You might need an oil cooler as big as your radiator to keep oil temps to 212F. Most seem to knock max temps down from ~275F to ~250F under track usage.

Attaching pic of graph showing the *same* oil pressure running 5w30 without an oil cooler at ~275F and with an oil cooler at ~250F, from this thread: https://www.ft86club.com/forums/showthread.php?t=91820

I understand at say 300°F as highest temperature without oil cooler, it would be better to have oil cooler and lower temperature. And at low temperature it would be worse to have oil cooler, pressure wise. What's the tipping point? 260°F? If so why?

Sorry about lots of questions, just trying to understand and thanks everyone for reply.

In my experience so far, these cars, last-gen and current-gen, are fine without running an oil cooler for track usage. Oil temp for me always climbs to 270-275F over a handful of laps and stabilizes.

If you're strictly worried about pressure, run 40-weight synthetic, it will give you higher pressure at 275F than 0w20 at probably 230F.

Me, I usually run 5w30 Redline (HTHS 3.7) at the track, though I have also done track events with Subaru 0w20....

[ruturaj001]

Originally Posted by ZDan

"lower" pressure isn't necessarily a problem, you only need pressure sufficient to keep the bearings fed. In the "working zone", hydrodynamic wedge is what supports the crank in the main bearings and the rods in the crank. HTHS is probably a better number to look at for oils to see how well they do there. Fixation on oil pressure and thinking "more is always better" is IMO somewhat misguided.


You might need an oil cooler as big as your radiator to keep oil temps to 212F. Most seem to knock max temps down from ~275F to ~250F under track usage.

Attaching pic of graph showing the *same* oil pressure running 5w30 without an oil cooler at ~275F and with an oil cooler at ~250F, from this thread: https://www.ft86club.com/forums/showthread.php?t=91820



In my experience so far, these cars, last-gen and current-gen, are fine without running an oil cooler for track usage. Oil temp for me always climbs to 270-275F over a handful of laps and stabilizes.

If you're strictly worried about pressure, run 40-weight synthetic, it will give you higher pressure at 275F than 0w20 at probably 230F.

Me, I usually run 5w30 Redline (HTHS 3.7) at the track, though I have also done track events with Subaru 0w20....

Thanks, I am looking at HTHS as well and sticking to >= 3.5.

Just for pressure argument sake, I looked at 300v 5w30 viscosity numbers and from that chart 240 is where pressure seems to be comfortably at what OP wanted (10psi/1000RPM), at 240F 300v should be about 8.11 cSt. Mobil1 FS 0W40 would have to be at 260F, and Pennzoil Euro L 5W30 would have to be at 250F for same viscosity. Both oils I have been interested in.

212F with oil cooler was a hypothetical best case scenario. By using same standards as above, with oil cooler temperatures would need to stay below 210F which seems is unlikely from your comment. So defeating the purpose of getting an oil cooler as oil cooler won't be able to compensate drop it caused.

[blsfrs]

Larger coolers do not necessarily produce a large pressure drop:

Setrab Pro Line Series 1 coolers measure 8 1/4" long (6 7/16" not including mounting tabs) x 1 7/8" thick. The female M22x1.5 ports are 4.8" center-to-center. This 72 row size measures 22 1/8" tall (not including the hex on the port fittings). This is the largest Series 1 cooler available. It is recommended for use on engines making up to 600 hp. Expect a pressure drop of 1 psi or less with this cooler.

@Ultramaroon has this one with a manual flow adjustment. I went with a series 1 Setrab 34 row cooler with the thermostatic sandwich. More and shorter rows results in less pressure drop.

I respect what @ZDan says about not needing a cooler with quality higher viscosity oils but I'm not yet brave enough to go coolerless.

[autoracer86]

230F-240F shouldn't be difficult to achieve with a good cooler on a NA car. Seeing as you have a 2nd gen the other thing you need to worry about is pressure drops due to G load at least that is what youtube says.

If it was me I would log the pressure you're seeing then post it here for some feedback. Maybe everything is fine and there is no need for any mods

[new2subaru]

I run a Jackson racing dual cooler NA and my oil temps are 230ish steady.

I use Mobil 1 0W-40

[blsfrs]

Originally Posted by new2subaru

I run a Jackson racing dual cooler NA and my oil temps are 230ish steady.

I use Mobil 1 0W-40

At that temperature, what does your oil pressure run?

[new2subaru]

Originally Posted by blsfrs

At that temperature, what does your oil pressure run?

No clue. Enough to keep the engine together lol I have about 40 track days on this car now.

ETA I would have plucked the info regarding the cooler and oil temps and pressures from this forum. I don't recall if there was any pressure drop at all.

[blsfrs]

Originally Posted by new2subaru

No clue. Enough to keep the engine together lol I have about 40 track days on this car now.

ETA I would have plucked the info regarding the cooler and oil temps and pressures from this forum. I don't recall if there was any pressure drop at all.

It seems some of the JR Dual rads have more pressure drop than others.

Just curious, have you done an oil analysis?