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Use 5w-30 instead of 0w-20?

104K views 56 replies 34 participants last post by  jogosub 
#1 ·
Turbocharged Foresters with the FB engine use 5w-30 oil. Do they have less problems with oil consumption? I'm thinking of switching from 0w-20 to 5w-30 to see if our 2013 2.5i would consume less oil. It doesn't use as much as some folks here but it seems to me that the heavier viscosity oil which is already being used in this engine would reduce consumption and I don't care about a slight loss of MPG.

Thought?
 
#2 ·
I've been having the same thought. My 2013 2.5 uses a little less than a quart during it's 7,500 mile OCI. The light will usually come on intermittently at about 5,000 miles indicating I am down a slightly over 1/2 qt. I know it's really nothing to worry about but it just bugs me after many years of driving cars with no noticeable oil consumption including my last 2 subies.
 
#4 ·
From Subaru Forester Owners Forum:

From what I understand this is just an issue with the 2.5i engine. I haven't seen anything on the 2.0 XT engine. Correct?

They seem to assume it is due to the different (2.0) XT engine. However, I believe the non-turbo 2.0 Imprezza has the oil consumption issue so it very well may be the 5W30 oil.
 
#6 ·
I think I would feel better using a Subaru recommended weight like the 5W30. It is Subaru recommended in the current US Forester Turbo along with the OB 2.5 in other parts of the world excluding the US. It sure makes it look like it has more to do with CAFE standards than anything else.
 
#17 ·
this has been the speculation the past as well, when specs for non-US markets were higher viscosities. Didn't know that has also been the case for the FB engines.

In Texas, my main concerns are 2 fold; if I use too-thin oil, am I gonna get more oil thru the PCV system when running at temp, and, if the oil is not 'heavy' enough, will it all drain from the bearing surfaces sitting in 105* heat all day - causing a brief dry-start when I go home from work?

More oil thru the PCV system will also lower effective octane of the fuel.
 
#8 ·
0w20 just is not going to be as stable over long-drain intervals. If your use of the vehicle is more strenuous, then I would expect the higher maint needs. If you are towing or stressing the engine over a long time, then a heavier oil might have some benefit. However, don't run to heavier oils, lighter oil lubricates better especially in modern engines with more exact tolerances... but just is not as sheer/burn-off stable. Keep in mind that as oil is "used" it will get thicker. 5w30 will end up closer to a 10w30 or heavier at the end of its life. You can use 5w30 but if your vehicle is still under warranty, then you might risk them denying a claim down the road. If it is out of warranty, feel free to use 15w40 diesel if you want. Oil generally is such of a non-issue now a days, it really does not matter for as long as it meets the API standard of the car's date. Even the SL oils are basically fine since they just have more Zn that can screw with O2 sensors over time.

I use as thin as oil as possible, even in my '99 OB. It gets mostly 5w20 with some 10wXX mixed in depending on the season. Winter gets straight 5w20 and the summer has a qt or so of 10w40 mixed in at the moment. With thinner oils, you exect a bit more "consumption" but that is not always a result from the engine burning oil due to an engineering issue. Keep in mind that some of the most notorious oil burners Toyota's "S" and even AZ engines are also know for being some of the longest lasting engines too.

My MR2 get 0w30 because it runs 3,750-4,000rpms on the interstate "fast" speed... and I only really drive it in the summer. I think Toyota has back-spec the 1ZZ-FE engine to 5w20 or less but it has not specifically been listed by Toyota in the models. New OB gets 0w20 and when 0w16 becomes available I will likely use that.
 
#9 ·
I'm thinking of switching from 0w-20 to 5w-30 to see if our 2013 2.5i
Check the owners manual. 5w-30 should be an option depending where you live. if so - run it. if it's a turbo engine - synthetic only. they have specific constraints driving those parameters that nonturbo engines don't have.

I always want it to and it never happens that oil viscosity and synthetic diff fluids help my fuel economy! So i wouldn't even worry about that, i'd be surprised to notice a difference.

Oil choice/viscosity is benign and is not where you'll find longevity, reliability, and add value to ownership.

If you're aiming for 400,000 miles or more then what you want a UOA on regular intervals to assess internal conditions and oil performance.
 
#10 ·

Pretty much every issue of Subaru Of Germany's 'Drive Magazin'
has a full page advert from MOTUL™ claiming that their 5W30 oil
is approved, by Subaru, for ALL Soobie gasoline and diesel engines.
(Not sure about model year 2015 -- they haven't been introduced
yet, in Germany.)

SUBARU empfiehlt MOTUL – der Schmierstoffproduzent hat
eigens für die Anforderungen von SUBARU das Motorenöl
„SUBARU by MOTUL 5W30“ für alle SUBARU Fahrzeuge
mit Benzin- und Dieselmotoren entwickelt.


Safari browser translation:
SUBARU recommends MOTUL - the lubricant producer
specifically for the requirements of SUBARU engine oil
"SUBARU by MOTUL 5W30" for all SUBARU vehicles
developed with petrol and diesel engines.


BTW, Sobaru of Germany also recommends a 15,000 km (9320 mi) OCI.


...OTOH, SOA dictates US warranty terms -- not Subaru of Germany,

Looby

 
#11 ·
My independent mechanic, a nationally known car guy who probably knows as much about engines as anyone, tells me that the exact weight of synthetic oil makes no difference. Synthetic is so good that as long as the weight is reasonable for the climate there's no practical difference.

I asked him why manufacturers such as Subaru specify such specific weights and he shrugged his shoulders. Same response I got from him when I asked why Subaru recommended brake fluid replacement at 30K. He knows from long experience that's not necessary.

As for oil consumption, he said don't worry about it unless it's really extreme. Much better to add oil between changes than to let dealership techs of questionable skill tear apart your engine.
 
#13 ·
I asked the local Subie dealer about using 5W30 oil instead of 0W30 - he said I would likely get an oil light indication from the higher pressure required to push the somewhat thicker 5W30 oil through the system.
 
#15 ·
2014 manual says you can temporarily use heavier oil to top off, but it recommends changing back to spec when you can.

The 3.6 (which already uses heavier oil) can go even heavier. I might try that next summer and see if it decreases my consumption. I go through about 1 quart in 2-2.5k miles.
 

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#18 ·
I asked the local Subie dealer about using 5W30 oil instead of 0W20 - he said I would likely get an oil light indication from the higher pressure required to push the somewhat thicker 5W30 oil through the system.
My goodness, what a dumb statement. Don't go back to that subaru dealer. First, I think that the oil flow in the engine is laminar. At laminar flow, the pressure at the pump is proportional to viscosity assuming the flow is constant. Therefore, the pressure at the pump would 50x higher at cold start up, such as 32 degF, then at operating temperature which is around 212 degF, as can be understood from the following data. How many people get an oil high pressure light at cold start up? Of course, the flow isn't constant because it's a cyntrifigal pump whose characteristics degrade with viscosity, but the point is that the pressure at the pump is very much higher at start up then at operating temperature.

At operating temp, the viscosity of the 0w20 oil is about 6 cst. [cst = centistocks which is just centipoise divided by the density]. At 120 degf, where the low temp light extinguishes, the viscosity is about 30 cst. At cold start up, at 32 degF, the viscosity is 300++ cst.

If you used 0w30 oil, the viscosity at operating temp [212 degF, would be about 50% higher then 0w20 or about 9 cst. Because the flow is viscous [I assumed], the flow would therefore be 1/3 less then for 0w20. But if the engine is OK with a viscosity of 30 cst at 120 degF, as implied in the manual, then obviously, a viscosity of 9 cst would be no problem. If as viscosity of 30 cst was a problem , then the manual would say not to drive at 70 mph until X minutes after the light extinguishes.

Assuming that I haven't confused everybody up to this point, the only question is the viscosity at 120 degF where the low temp light extinguishes. So for 5w30 or 0w30, one would only have to drive slowly for another 30 sec after the light extinguishes, before putting the accelerator to the floor to make sure that they were below 30 cst viscosity. Of course, that assumes that one trusts that the low level light is set correctly to allow full speed without damage to the engine.
 
#34 ·
My goodness, what a dumb statement. Don't go back to that subaru dealer. First, I think that the oil flow in the engine is laminar. At laminar flow, ...... would only have to drive slowly for another 30 sec after the light extinguishes, before putting the accelerator to the floor to make sure that they were below 30 cst viscosity. Of course, that assumes that one trusts that the low level light is set correctly to allow full speed without damage to the engine.
Thank you for injecting some sanity into an oil thread.

Motorcyclists are even more OCD about oil. They completely obsess about it to the point that it is a common joke in motorcycle forums about "another oil thread".

A motorcycle-oriented magazine similar to Consumer Reports did a series of studies about performance of oils a while back, comparing viscosity change, base package depletion, and anti-wear additive packages and depletion.

IMO, the gist of the research was:
1. ALL oils suffer from a rapid and significant shear viscosity change within the first thousand miles. So a 20-50 oil quickly becomes a 10-40 oil, then becomes a 5-30 oil somewhat less quickly, then .... ALL OILS THIN PRETTY QUICKLY.

2. Base package depletion is largely a measure of length of drive. Lots of short trips will deplete this much more quickly than highway miles (duh).

Most motorcyclists choose to use a slightly thicker oil because economy is less important than protection.

So it appears (IMO) that the specification of thinner oils is all about fuel economy.

My $0.02. YMMV. etc.
 
#19 ·
Axiom: Mechanics are Luddites :)

The problem is piston ring tension and not 0w20 oil. I will use at least a 10w30 that does not shear ("Resource Conserving" oils shear to 20 oil in a few hundred miles and the VII polymer shear breakdown is a precursor of sludge)...Or I will stick with proper Mobil 1 0w40 for long-drain and shear stability and proper oil film thickness. I am interested to know what is required in Germany for the 2015 Outback, as well...But Europe is moving to Euro6 standards so they are also under pressure to prioritize fuel economy/emissions over engine protection.
 
#21 ·
Axiom: Mechanics are Luddites :)

The problem is piston ring tension and not 0w20 oil. I will use at least a 10w30 that does not shear ("Resource Conserving" oils shear to 20 oil in a few hundred miles and the VII polymer shear breakdown is a precursor of sludge)...Or I will stick with proper Mobil 1 0w40 for long-drain and shear stability and proper oil film thickness. I am interested to know what is required in Germany for the 2015 Outback, as well...But Europe is moving to Euro6 standards so they are also under pressure to prioritize fuel economy/emissions over engine protection.

No decent current synthetic oil has any appreciable VII in the mix. Base stocks for good grade III oils have a wide enough VI that 0w/40 is easily achieved without the addition of VII. 0w/20 does not contain any VII, and neither does any name brand 0w/30 or 0w/40. So, a name brand synthetic oil will not shear appreciably in the length of a mandated 7500 OCI.

Plenty of oil analysis confirms that VII shearing in Subaru engines is not an issue........The oil comes out maintaining the full viscosity that it went in with.
 
#22 ·
So much debate about the oil - I have the 3.6 engine and according to Subaru I should use conventional oil with a 7500 mile 7.5 month change schedule (after 3000 miles 3 month change) - Same if I use synthetic oil. BUT the dealer says 6 month 6000 mile change schedule after 3000 mile change.
another can of worms opened ..... :rolleyes:
 
#23 ·
Actually your situation is clear cut. The manufacturer underwrites the warranty, not the dealer. So do what the manufacturer says, and ignore the dealer.

No point in spending extra for synthetic until the warranty runs out. Once that happens, you can switch and change it out half as often to save money.

Back to the discussion at hand...

If the US market is the only place Subaru is pushing 0w-20 for these engines, I'd be even more encouraged to try 5w-30 to see if it reduced consumption.
 
#24 ·
If this independent mechanic doesn't know why brakefluid must be periodically changed, then one should question the validity of his statement(s) on engine oil.
He knows, of course. 30K is just way too early, except for the dealers' income, based on his decades of experience. He just hasn't seen problems with brake fluid at these mileages, on Subarus or other makes.
 
#25 ·
It is a 15 minute job, using $5-7 worth of materials. It is wise to do it earlier rather than later, especially in a damp climate. If you do it yourself, that is........A dealer will charge an outrageous fee. I would be curious what your independent guy charges for this.
 
#27 ·
Brake fluid is still the same age-old base, being hygroscopic (and not just based on mileage). You may not feel degradation, but 36mos/36K bleed/flush is old school.
The brake/fluid is an open/non-hermetic system, it will trap air (through the lines) and promote corrosion. Moisture has air, bleeding expels the air/corrosion.
What is you mechanic’s rational other than ‘unnecessary’?
 
#40 ·
I will point out that for you turbo folks - This is why you want to use an oil that doesn't shear down, because your turbo will do a similar think as the gearboxes to you oil weight. And why you need to change your oil more frequently...
 
#41 ·
5w30 in FB25 Engine 2014 Outback

Hello,
I just like many of you have spent too much time researching the 0w20 oil use and the "Perils" of using 5w30 oil in the new motors and have this to throw in the ring;
I have been using a 5w30 full synthetic in my 2014 Outback FB25 motor and without getting any oil wars, it is safe for me to say the car has been running just fine. I think it seems smoother and more refined but that is just my personal take. I was surprised in doing my research that I kept reading how 5w30 thins down to a 20 weight in short order. If you look at the many Blackstone oil analysis reports that have been posted there doesn't seem to be the viscosity thinning that seems to be brought up so often. Maybe it's just the ones I read or maybe it's just not as bad as one would think.
I have worked with engines for over 35 years and have rebuilt dozens all that lived long happy lives. I sold filters from Fram, Baldwin, Luber Finer, and Air Refiner. I haved been to factories and have seen the different processes and I feel comfortable in saying the factory filter (Blue) despite not as robust looking inside as the metal end cartridges will certainly get the job done and Subaru knows why it wants the higher bypass setting. If you can, try and stick with that setup until some nice high capacity filter arrives complete with synthetic media.
As for the oil, I know it has been talked to death so in that case I went with what I have learned over the years and a few phone calls to my old colleagues .

Good luck everyone, Subaru does make a pretty rugged car.. Enjoy it!
 
#42 ·
"I feel that...." - "I believe that...." - "I heard that...."

The scientific method and chemistry/physics degree need not apply...That is the extent of motor oil discussion at Bob Is The Oil Guy...LOL! Many of the posters over there are downright stupid.

I am still waiting on the Outback oil specs out of Germany....
 
#44 ·
I am still waiting on the Outback oil specs out of Germany....
Not official corporate specs, but MOTUL's ad runs in every
issue of the German edition of Subaru's Drive Magazin.
It claims that Subaru recommends their 5W30 for use in
all Subaru engines -- gasoline or diesel.

Google translation: (see page 43 of above link)
"Subaru recommends MOTUL-- the lubricant producer
specifically for the requirements of SUBARU engine oil
"SUBARU by MOTUL 5W30" for all SUBARU vehicles
developed with petrol and diesel engines."


AFAIK, 2015 OB hasn't yet been introduced in Germany.

...the web knows all.

Looby
 
#43 ·
I KNOW that my car used a Qt and a 1/2 twice between changes w/ Mobil1 Extended protection full syn. I changed to Castrol Extended protection full syn and the next 2 changes used less then 1/2 qt 2010 2.5 5w30 in both cases and approx 5-6k between changes.

So brand seemed to make a big difference, as far as use of oil between changes.

I check the level weekly and top off if 1/4 qt low always.
 
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