Why Rotella 5-40 for turbo Subaru?

[bluemanchu]

Hello all!
I've been lurking for a while and finally found a question i couldn't answer by searching.

I constantly see Rotella 5w40 highly recommended for turbo subarus, but have never seen a real reason for it. Mostly people say that Subarus like this oil, that it smooths out the engine, or that the engine sounded much better. Which, to me, seems a bit subjective. So what i'm asking is why do subies like a 40wt oil for DD with a cSt at 100 of 14.56 (VOA on this site) when after reading this (http://tinyurl.com/oil-stuff) the author, who i see is also on this board

, states that "automotive designers usually call for their engines to run at 212 F oil and water temperature with an oil thickness of 10"


I guess its really just a curiosity thing b/c someones engine surely would have overheated by now if it was too thick, but is there any real reason for it or is it just a trial and error thing?

thx much

 

[JimPghPA]

The temperature that the oil is exposed to when it goes through the turbo to lube it when up to temperature and also the ability of the oil to flow at the high RPM's of a trubo when cold probably are some of the main reasons that any oil for any turbo engine woule be chosen, along with how it performs for the rest of the engine.

 

[bluesubie]

Most Energy Conserving oils don't hold up that well in a hard driven turbo in a lot of driving conditions. RTS has higher levels of Anti-Wear additives, is cheap, and is API SM rated. 40 grades are also allowed according to the manual.

-Dennis

 

[Johnny]

Wow! You have been a member for two and a half years and this was your first post.

 

[sxg6]

I think most of it is in their heads. Rotella 5w-40 is a very good oil, but if you were to swap out their rotella with conventional 5w-30, I bet 9/10 wouldn't notice. I see it frequently on a few subaru forums when people talk about oil. I use "_____" oil and my car loves it! Ok.. how exactly does your car love it? Right now I'm running Mobil Clean 5000 10w-30, and I like it because it has reduced my oil consumption.

 

[Thermo1223]

It is not in my head...

All of the 5w30's I ran made the engine feel really harsh when pushed. RTS...it is smoooth as butter.

Car loves it because car runs better on it, simple truth.

 

[bluemanchu]

Thanks for the welcome! Yeah I do tend to read a ton and not post much unless i can't find an answer.

 

[mechtech2]

People don't primarily use this oil because of smoothness or feel.
They use it in turbo'd engines because it makes sense with the high heat encountered [some area are VERY high heat].

 

[Thermo1223]

Originally Posted By: mechtech2
People don't primarily use this oil because of smoothness or feel.
They use it in turbo'd engines because it makes sense with the high heat encountered [some area are VERY high heat].


Well that is a given...

Many syns out there to choose from but the T6 seems to be a winner in Subarus.

 

[Eddie]

Woder id it would be a better oil than PP 5w30 in my Mazda CX7 turbo?

 

[bluesubie]

Originally Posted By: sxg6
I think most of it is in their heads. Rotella 5w-40 is a very good oil, but if you were to swap out their rotella with conventional 5w-30, I bet 9/10 wouldn't notice. I see it frequently on a few subaru forums when people talk about oil. I use "_____" oil and my car loves it! Ok.. how exactly does your car love it? Right now I'm running Mobil Clean 5000 10w-30, and I like it because it has reduced my oil consumption.

Um, the "I use ____ and my car loves it" is said a lot on here as well.

Just compare uoa's on Energy Conserving oils in Subaru turbo's vs. uoa's on RTS, GC, etc. The 8k uoa on RTS in a modded STI was impressive. No way would I run Clean 5000 in my turbo.

-Dennis

 

[sxg6]

I agree, people here say that a lot as well. And just to clarify a few things.. I have a non turbo legacy, that's why I run just regular conventional. I agree that turbo subies are tough on oil, and it is a good idea to run a stout oil if possible. I guess what I take issue with is when people justify using an oil because it feels smoother, or the engine sounds quieter. If you were to run a uoa on the oil that makes your car "noisy", vs the oil that makes your car "quiet", I'd bet a lot of $$ that the wear numbers are very similar.

 

[oggb]

I would think it's more of an HTHS issue. 0/5/10W-30 oils tend to have fairly low HTHS ratings vs. things like Rotella T6 and Mobil 1 TDT.

Makes sense to me anyhow. The higher the HTHS the better for something that's turbocharged and will see high load more often than your run of the mill passenger car.

Also, somewhere it was remarked that Subaru EJ20T and EJ255/257 engines have somewhat narrow bearings for the amount of power they produced due to the compact design of the engine. I'll have to look around and see if I can find that.

 

[Gary Allan]

Why Rotella 5-40 for turbo Subaru?

Cheap and mostly bulletproof for the application. If they're (they being Subaru) going to sweat 3500 (or was it 3000?) mile OCI's ...you might as well hit it with a sledge hammer and relax. Cheap and effective.

Of course, if you're of a more cultured persuasion; having ..shall we say, distinctive tastes, then perhaps uncorking something like M1 0w-40 might be in order ..but with those pesky short OCI's ....well, let your conscience be your guide. How can you put a price on proper lubrication

?

 

[gathermewool]

Implying that M1 0W-40 is better than T6 made me smile; thanks for the humor

The new "required" interval for all turbo Subies is their severe service interval - 3750 miles. This, from what I've read, is based on turbo-feed-line screens )(only found in some not all turbo Subies) clogging and restricting flow, leading to turbo failures. This may not be the entirety of the reason, but it's what popped up when I searched a while back.

Also, IMO, the change was due to those in non-WRX turbos running bulk oil to the normal service interval of 7500 miles, and never checking the screen.

I could be wrong, but if a UOA shows the oil has life left, then I don't believe this is an issue. I run T6 out to 7500 miles (including a lot of highway) in my 08 STI, FWIW

 

[bluemanchu]

Thanks for all the info guys. I read up on HTHS, thanks for pointing me in that direction. So a 40wt wouldn't cause too much pressure if someone was just driving normally with a few autox here and there?

You are correct about the OCI and the turbo oils inlet screen. However they stopped using them in the 06 models. I've done 4-5 06/07 WRX turbo upgrades and none had screens in them. So i have no idea why they haven't changed the lengthened the interval. Oddly enough they did change the current model's coolant change interval to 11 yrs or 137,500 miles from 30,000 miles.