M1 15w50 in a turbo subaru 2.5 liter - 3 season?

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Feb 6, 2008
Hi all,

I picked up 3 quarts of Rotella T 5w40 at Walmart today (enough for 2 oil changes and a little make-up oil).

Anyhoo, while I was there I saw M1 15w50 for $26. Not cheap, but only a few bucks more than Rotella's true cost.

I've read on here that their 15w50 is a fantastic oil and can be used widely with confidence.

I was wondering about using it in my 2008 Subaru Legacy GT during April-October (i.e. no lower than 40-45 degrees fahrenheit likely).

My main concerns with this engine are:

Premature turbo failures - I want an oil that can hold up in that turbo under less than ideal circumstances.

Lean running #2 cylinder - The stock ECU mapping lets one cylinder run leaner than preferred, and I want an oil that can take the resulting heat.

I'll be tuning this engine eventually (i.e. out of warranty probably), which will take care of the lean condition. But I'd prefer to maintain it to a T until I don't have to worry about voiding a warranty, and to prepare it for the later usage.

Thoughts on using this oil in this app in PA?
I wouldn't go THAT thick on a brand-new engine. M1 0W-40 is about as thick as I'd go - its a good, robust oils as well.

Does your Manual allow for the use of 50-weight oils? You say you're not going to tune it until its out of warranty, presumably to keep you warranty good - why risk the same thing with your oil choice?
The engine is allowed (and could be said to be encouraged) a 50 weight under "extreme" conditions.
How much horsepower is that turbo Lagacy making and are these engines know for turbo failure ?

Off topic: 15w50 Mobil 1 is $2.50 on closeout at Walmart
Excuse me, it says in the manual "Severe Driving Conditions", desert areas, high temperatures, , or heavy duty applications:

SAE 30, SAE 40, 10w50, 20w40, or 20w50 API SM or SL
Originally Posted By: LT4 Vette
How much horsepower is that turbo Lagacy making and are these engines know for turbo failure ?

Off topic: 15w50 Mobil 1 is $2.50 on closeout at Walmart

Not at this walmart....else I would've bought a few :)

The Legacy is making ~243 HP/241 torque (SAE) stock.

These particular turbos DO seem to be identifying themselves as having a good potential for turbo failure around 60-100k. There is a known issue involving a factory filter inside a banjo bolt that feeds the turbo. The filter is not a service item, and appears to become clogged on SOME cars, resulting in insufficient oil flow.

Obviously, a good idea is to check/replace the banjo bolt/filter at a certain interval.

Anyhoo, synthetics excel when A. running long intervals or B. things go wrong. I want to make sure I've got a lubricant that maintains it's integrity when I've got a cylinder running hot or a turbo getting insufficient flow.

Hoping to get input on M1 15w50 :)
Pickled - Well deserved razzing :)

My secret is that I'm using 3 quarts of Extra Virgin Olive Oil in my engine, and then I top it off Rotella T synthetic.

Runs SOOO quietly!
Turbo will last a life time on the olive oil regimen...no clogged arteries (mmm I mean U-bolt filters) for sure!
If the manual allows it, then 15W-50 M1 would be a great oil for a turbo - even though it is a 15W oil, it still has excellent cold-flow characteristics that I've read make it 'closer' to a 10W...
Frank should be along shortly to talk about that oil. Appears he's had a lot of experience with it in cars that don't spec it. Since the subie specs it I would use it with confidence.
Specs it for severe driving. The irony is that all Subaru turbo cars switched to the "severe driving" oil change schedule in, IIRC, 2007, which is 3750 miles.

I'm hoping that it's a good choice for this engine in a 3-season usage pattern.
I think if you were going to see premature turbo failure, you probably would have seen it already. Although I haven't been following the LGT's as closely, haven't the problems been with fairly low mileage?

There have been a couple of uoa's here with very high lead, IIRC, on cars that were supposedly not affected by the stop sale and the mileage was low.

I would also like to know what good insurance would be as well since my first turbo lasted only 65k miles. I ran GC for about four years or so and had a turbo seal problem. Excess oil was getting past the turbo and smoking like crazy on occasion. The head tech at my dealership said that I shouldn't need to go higher than an xW-30, but he was puzzled as to why I had a seal problem. I have all of my banjo bolts (turbo and AVCS) and everything looked fine. My dealer has only seen issues in them with "abused" cars. I ran GC, and now SSO, to 8k intervals with good uoa results. I'm still thinking Xw-40 diesel for my next oil.


From what I've read, I believe you're right about going for a tune though. No comment on the M1 15W-50. I don't want to go higher than an xW-40.

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Hey Dennis,


Here's a link to a thread where there are 79 blown turbos vs. 327 without. Most of the blown turbos happened between 40-80k.

On the Legacy GT, it's as I said. It's not related to the stop sale (bad main bearings, IIRC). As best can be determined it is related to the oil supply coming through a banjo bolt filter which can become clogged or suffocate sufficient flow.

Further, in Ex-US countries, the recommended viscosity for these engines is 5w40/10w40 and not 5w30.

From what I understand, the only way a UOA would show a pending turbo failure is to show elevated silver. But I tend to think the failures are catastrophic, and happen within a short period of time. I also don't know the tendency for silver to dissolve into the oil and therefore show up in a UOA.

I don't know. I just want no engine problems for as long as possible.

Originally Posted By: JoeFromPA

Here's a link to a thread where there are 79 blown turbos vs. 327 without. Most of the blown turbos happened between 40-80k.


Hadn't realized it was that bad on the LGT's in regards to the clogged screens. At quick glance I recognize a few of the screen names, including Opie (works at a dealer). Any idea what oil he's running?

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