Just because 275-300 is maybe ok doesn't mean it is ideal. Your oil WILL start breaking down at those temperatures. How about running that known-good synthetic 30- or 40- weight, with a simple air to oil cooler at 200-230 temps for maximum reliability?

Oil doesn't necessarily breaks down at those temperatures. It depends on the oil, people have had good results in UOA after 5k miles and hitting 300 few times on M1 FS 0W-40. Sure I want maximum reliability but I don't think oil cooler means maximum reliability.

pretty wild to think that some of these people run their engines above 230+

I had oil analysis done with 4400 miles and 6 track days (with ~270F oil temps) on the oil (at 7200 total miles after first oil change at 2800 street miles). This was with Subaru 0w20 synthetic. TBN "plenty strong" after that. Per Blackstone: "TBN stands for Total Base Number and measures the amount of active additive present in the oil. It’s a good test if you want to run your oil longer than you normally do."

cSt at 100C is a bit thin though. FWIW I asked for 5w30 and Subie service desk guy said "no prob", but after I got this report I went back and looked at the invoice and it listed 0w20, in retrospect not surprising the techs put in the oil Subaru dictates...

Not as wild as running at oil pressure of 46psi or lower at 6500 rpm at 230. 46 psi is with air to oil cooler, the coolant-oil cooler has even bigger pressure drop. I don't think engine is built for pressure drops, at least quality euro spec or full saps oils are made for high temperatures (as high as 300F on non racing oil).

:lol:

IMO the reliability of an aftermarket oil cooler is *way* more suspect than the reliability of running synthetic oils up to 275F *calculated*, 255F sump temp.

A quality conventional motor oil will tolerate oil sump temperatures up to 250 degrees, but starts breaking down over 275 degrees.
A full-synthetic oil will withstand sump temperatures in excess of 300 degrees
https://www.motortrend.com/how-to/en...0260%20degrees.

What is the reliability concern with an air to oil cooler? You seem to be taking a this OR that position, when a this AND that position may be best.

I'm sure you read this from that article "The traditional approach is to try to hold oil temperatures between 230 and 260 degrees".

That was in context of conventional oil. Synthetic was in next paragraph and racing oils seems to hold to 350+ from the article.

Do a search and you will find that plenty of people have had problems with leaks. Other issue is that oil is slower to get to operating temp. That "Savagegeese" guy became annoyed with his initial FT86 because he (wrongly IMO) thought he *had* to have an oil cooler, installed one, removed it in the winter because oil didn't get hot enough, and then it leaked when re-installed.

Here is the context:
https://www.motortrend.com/how-to/en...0260%20degrees.

"A quality conventional motor oil will tolerate oil sump temperatures up to 250 degrees, but starts breaking down over 275 degrees. The traditional approach is to try to hold oil temperatures between 230 and 260 degrees."

They're talking about non-synthetic, and they're talking about oil temperature in the pan.

Regarding synthetic:
"A full-synthetic oil will withstand sump temperatures in excess of 300 degrees, and for hardcore professional racing, some oval-track race teams are experimenting with ultra-thin, specially formulated, race-only synthetics operating at 350 degrees or even higher."

So you'd recommend that I uninstall my oil cooler (HKS) for track driving, as long as oil temps don't exceed 300*F?

If it's working fine and not leaking, and there are no vulnerable lines running under the car, and you don't drive it in the colder months, nah, I wouldn't necessarily recommend removing it if it's not hurting anything and the oil temp always gets up to ~190F reasonably quickly.

Do you track the car? Personally, if I turbo'd mine, I'd first see what the oil temps did at the track without a cooler first, and if they stabilized comfortably below 300F then I probably wouldn't bother with one. Above 285F I'd definitely go to 40 or 50 weight though.

Might be best to evaluate using pressure sensor. Then consider pressure at different temperature and RPM with and without an oil cooler, and if it actually reaches 300F.

Heavily track the car (drifting), but also summer street car, using M1 0W-40. HKS is thermostat, so gets up to temp quickly, and I usually peak around 240*F (measured at sandwich plate) although I have seen higher. Pre-turbo I was getting up to 250F, so I just did cooler at the same time as turbo.

That's where I'm sorta coming from. Its not hard to ensure an oil cooler isn't leaking or having vulnerable lines. So with that said...seems oil temps of 220-240 are highly preferred (although not necessary) compared to 280-300F.