08 Subaru STI oil recommendation

[53x19]

Hi,

I have an 08 STI that is about to wrap up the break-in period. I’ll have a Cobb stage-1 tune on it after the break-in period (~+12% hp). I don’t plan on any other mods and want to use synthetic oil. I will be driving the car fairly hard with some autocross from time to time. I’d like some opinions on a few questions/assumptions I have:

The manual says 5w30 is recommended. It is the same oil my wife’s 2007 NA 170hp Integra uses. Considering the high output, I feel I should run a heavier weight. 5w-40 seems like it would be perfect for the hot (100+F) / cold (-10F) Denver weather. Am I off here?

Is there any harm in going with a non API-SM / ILSAC GF-4 spec oil? Will that damage my catalytic converter? None of the 5w-40 blends I’ve looked for meet those standards. I have found plenty of 5w30 and 10w-40 oils that meet the specs, but no 5w-40. Should I just alter between those weights with the seasons?


Thanks

 

[d00df00d]

I guarantee you the kind of 5w30 you'd use in your STI is a far cry from the kind your wife's Integra uses. Don't worry about them being similar just because they have the same weight.

You could go heavier and protection might increase in some cases, but so will heat and parasitic drag. Also, heavier weights just won't flow as well when cold; 5w-40 and 0w-40 are okay but still not as good as most xw-30s, and they always contain a lot of viscosity index improvers that can shear out, leaving your oil thinner and possibly forming deposits.

Non-API SM/ILSAC GF-4 oils will not damage your catalytic converter per se. The worst that will happen is that your catalytic converter might not last quite as long.

I'd recommend sticking with an xw-30 viscosity and just getting a really really good one. There should be no reason to switch weights with the seasons.

Here's my hit list:

- Motul X-Max 5w30 (best balance of everything, expensive)
- Motul 300V 5w30 (best performance, shortest OCI, most expensive)
- Castrol Syntec 0w30 European Formula (excellent performance, most widely available, cheapest)
- RLI BioSyn 0w30 (better than the X-Max and Syntec above, and made from renewable resources)
- AMSOIL Signature Series 0w30 (probably the best cold flow and OCI, very new so kind of a wild card)

 

[bluesubie]

Are you planning to stick with Subaru's new 3,750 mile OCI for turbos? 5W30 is preferred fuel fuel economy and higher viscosity oil is required for high temps and severe condtions.

Syntec 0W30 (GC) has shown good used oil analysis in STi's. It's a GF-3/SL oil if that's a concern for you.

-Dennis

 

[Titan]

It would be getting GC 0-30 or Pennzoil Platinum 5w30; if it were mine.

 

[53x19]

Originally Posted By: bluesubie
Are you planning to stick with Subaru's new 3,750 mile OCI for turbos? 5W30 is preferred fuel fuel economy and higher viscosity oil is required for high temps and severe condtions.

Syntec 0W30 (GC) has shown good used oil analysis in STi's. It's a GF-3/SL oil if that's a concern for you.

-Dennis


I do plan on following the 3,750 change interval.

 

[bluesubie]

In that case, I wouldn't spend too much money on oil if it were me. You can usually get GC for less than $5.00 on sale. Pennzoil Platinum is usually on sale a lot as well. Although the 5W40 is hard to find, but you could thicken up the 5W30 with 15W50. I've seen good used oil analysis on nasioc with xW30 and xW50 combinations. You can do a used oil analysis to determine viscosity, although some Subaru's will still show high wear metals the first 8-10k miles.

Heck, I'm not sure I would even run synthetic at 3,750 mile intervals. Rotella convetional 10W30 would be good if you can find it. Subaru of America and their new OCI.

Oh, and

.

-Dennis

 

[d00df00d]

Originally Posted By: bluesubie
In that case, I wouldn't spend too much money on oil if it were me.

...

Heck, I'm not sure I would even run synthetic at 3,750 mile intervals. Rotella convetional 10W30 would be good if you can find it. Subaru of America and their new OCI.

When the manufacturer recommends such a short OCI, it means that conditions in the engine are very harsh and/or they want to account for people using cheaper conventional oils that may not be up to the task.

Plus, it is after all a relatively small displacement/high specific output turbo engine that is about to receive an aftermarket tune.

To me, that says you definitely want to spend the money on a good synthetic oil...

 

[bluesubie]

Not really the manufacturer, but the U.S. headquarters. I think the "cheaper" oils comment is right on though. Plus a combination of owner oil neglect/abuse in these cars over the years, which Subaru even mentioned in a tech bulletin IIRC.

Subaru does allow a wide range of viscosities though. Subaru of America is only 2 mpg's over the CAFE minimum, which is probably why 5W30 is listed as "preferred for fuel economy".

-Dennis

 

[JSRT4]

If it was my car and I planned on keeping it for a long time, I'd run Mobil 1 0w-40, not overly viscous despite the 40 weight label, and it works well in turbo applications. I'd run it for 5,000 mile intervals minimum, not any shorter than that.

If you plan on sticking with an OCI less than 4k, then a less expensive 30 weight such as GC or PP is likely your best choice. Synthetic oil all the way, whatever you end up choosing.

The manufacturer of my 2.4L turbo engine recommends Mobil 1 0w-40 for 10,000 mile OCI's, I'll probably run it for 5,000-7,000 mile OCI's.

 

[53x19]

Originally Posted By: bluesubie
Not really the manufacturer, but the U.S. headquarters. I think the "cheaper" oils comment is right on though. Plus a combination of owner oil neglect/abuse in these cars over the years, which Subaru even mentioned in a tech bulletin IIRC.

Subaru does allow a wide range of viscosities though. Subaru of America is only 2 mpg's over the CAFE minimum, which is probably why 5W30 is listed as "preferred for fuel economy".

-Dennis


Insightful... I hadn't considered that.

 

[MGregoir]

Mobil 1 0W-40, changed at 3750 miles...safe better than sorry, and better than warranty.

 

[d00df00d]

Originally Posted By: bluesubie
Subaru does allow a wide range of viscosities though. Subaru of America is only 2 mpg's over the CAFE minimum, which is probably why 5W30 is listed as "preferred for fuel economy".

Ah, okay. Makes sense.

 

[SuperEd73]

I have an '02 WRX and 5w30 is the "preferred" oil for the 2.0 liter turbo as well. They also do list oil weights all the way up to 20W-50 for use in high temperature areas however. IIRC my warranty book lists the "severe" oil change mileage at 3,750 as well. There was no requirement for the EJ20 to follow the severe schedule at that time but I guess Subaru has learned a few things over the past few years.

Check around on the used oil analysis forum, there are a few used oil analysis on Subie turbo engines.