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Old 11-22-2010, 10:54 PM   #1 (permalink)
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Default Oil Change Interval...

Yes, I've already searched and read all about it. I know exactly what Subaru Inc. says, and when they said it.

So far I've changed my oil every 3,750 miles, as ordered. I use only Subaru filters. I just switched to synthetic.


Here's the question:

Assuming that I'm using quality synthetic, why NOT extend the oil change interval?

I understand the problem with the filter in the banjo bolt, which is why Subaru originally halved the oil change interval.
Most of us have now removed the filter, so this is now a non-issue, right?

I understand that changing the oil and filter frequently is good to do to get rid of contaminants and so that the filter doesn't fill with crud, but assuming that used oil analysis says that the oil is OK, then where's the problem?


I'm considering extending my oil change interval to 5,000 miles, doing a used oil analysis, and then extending it further if the analysis is good...

Thoughts?

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Old 11-22-2010, 11:27 PM   #2 (permalink)
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Turbos are much harder on the enigine oil. This is normal for a turbo, any turbo. You can extend it at your own risk.

Oil does many things. It removes dirt and holds it in suspension, it lubricates and cushins parts. and the biggy for a turbo, it cools parts. It cools the turbo bearings and the pistons. That is a lot of work for oil, so it needs to be changed more often. Turbos also consume more oil (see previous comment) and people don't check the levels.

All these reasons apply.
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Old 11-22-2010, 11:57 PM   #3 (permalink)
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also, shear stress. this is a microscopic effect on oil. motor oil has molecules in long chains. as long as those chains stay long, they hold their viscosity. but heat those molecules and rub them between two pieces of metal, and you're going to start tearing the molecules apart into smaller and smaller pieces. this is shearing.

the harder the oil has to work (like nipper said, lubricates, cushions, and cooling), the more the oil will experience shear stresses, and the faster it will break down and lose viscosity. a metal turbine that spins at 30,000 RPM (or whatever ridiculous speed they run at) is going to do this QUICK.
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Old 11-23-2010, 01:33 AM   #4 (permalink)
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Thanks, guys...

I check my oil frequently, so I'm not worried about the level running low.

I understand that turbos are harder on oil than NA engines, but I also know that a lot of cars with turbos use synthetic and have oil change intervals FAR longer than 3,750 miles.

I know, apples and oranges... but oil analysis would reveal a loss of viscosity or other breakdown, right?

Teach me, please,

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Old 11-23-2010, 02:24 AM   #5 (permalink)
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Quote:
Originally Posted by Bimmer View Post
Thanks, guys...

I check my oil frequently, so I'm not worried about the level running low.

I understand that turbos are harder on oil than NA engines, but I also know that a lot of cars with turbos use synthetic and have oil change intervals FAR longer than 3,750 miles.

I know, apples and oranges... but oil analysis would reveal a loss of viscosity or other breakdown, right?

Teach me, please,

Bimmer
yes, absolutely. A UOA will tell you exactly what viscosity the oil has broken down to. Blackstone labs will tell you if it's within reason or not as well.
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Old 11-23-2010, 08:11 AM   #6 (permalink)
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^+1

Everything mentioned here is a valid point, but a UOA will let you know how your oil is holding up.

There is one other thing to consider. There is another banjo bolt going to the AVCS system that can clog as well. The plus side is that if it clogs, you get a CEL and a loss of performance but no destruction. IMO the turbo subaru is not a harsher environment than every other turbo car. Other turbos use oil in the same way that Subaru does and none of them give such a short OCI. SOA originally required 7500 for all turbo cars or 3750 for extreme conditions such as hard driving in hot areas. It wasn't until the TSB on the banjo bolt that they classified all turbo cars as extreme conditions and changed the OCI.

Yet another issue which requires more frequent oil checking is fuel dilution. It will slowly thin out the oil which will in tern increase the fuel dilution and could lead to consumption. Subaru's are apparently more prone to this because of the tolerances that they allow in their engines. So especially for the first time you do this, just check every time you get gas or every couple of days. It sounds like you already do this though.
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Old 11-23-2010, 08:15 AM   #7 (permalink)
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Quote:
Originally Posted by Seabass View Post
IMO the turbo subaru is not a harsher environment than every other turbo car. Other turbos use oil in the same way that Subaru does and none of them give such a short OCI. SOA originally required 7500 for all turbo cars or 3750 for extreme conditions such as hard driving in hot areas. It wasn't until the TSB on the banjo bolt that they classified all turbo cars as extreme conditions and changed the OCI.
Yep, I was shocked to read about 3750 oil change intervals for the XT when I was Outback shopping.........thats ridiculous!
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Old 11-23-2010, 11:53 AM   #8 (permalink)
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Yes she's a high maintenance girl (premium fuel too)
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Old 11-23-2010, 12:20 PM   #9 (permalink)
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Two other thoughts:

1. Warranty: As a 2008 I bet you're still under your powertrain warranty. Don't mess with that. Don't give SOA anything to question re: turbo oil changes.

2. Didn't the oil change interval for 2011 turbo's just change to allow 7,500 mile changes under the right conditions and also require synthetic? Food for thought, but I don't think the wrangling would be worth it because of your 2008 requirements.

Re: oil shearing and oil use as mentioned above. I don't have a turbo but have done a lot of reading on NASIOC and Legacy GT boards and Forester boards. And here's what I see. A lot of people who buy turbo's in the WRX, Legacy and Forester crowd run the P*** out of their engines. I get the feeling WOT is is what the engine sees a lot of. Subaru knows this and so besides the banjo bot issue they wanted 3,750 oil changes on conventional oil. Now that they have switched to synthetic being required they allow the 7,500 changes. But they still want oil changes before and after a track day (which I think a lot of turbo's see anyway). This should tell you something.

So based on WOT percentage and a UOA you might could tailor your oil changes but only after your warranty has timed out.
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Old 11-23-2010, 03:21 PM   #10 (permalink)
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Quote:
Originally Posted by number 41 View Post
Two other thoughts:


2. Didn't the oil change interval for 2011 turbo's just change to allow 7,500 mile changes under the right conditions and also require synthetic? Food for thought, but I don't think the wrangling would be worth it because of your 2008 requirements.

.
No and yes. Starting 2011 it is recomended that all subies should be on synthetic and required for Turbo the oil change interval did not change.
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