Manual recommends 5W30 year-round in Impreza

Lighter oil may also drain from parts faster exposing more metal-metal surfaces, allow more blow-by, and suffer breakdown at high temps.

many models here in the states that say use a light weight oil, recommend a heavier weight when sold overseas.

I think the CAFE rules are the primary driving force behind the stateside switch to lighter oils - there is a small but measurable increase in gas mileage. Still, it may only mean you get 250K miles instead of 300K miles of engine life - who knows?

Carl

1 Lucky Texan

Edward Hayes wrote:

My WRX manual says that 30, 40, 10W-50, 20W-40, or 20W-50 can be used for extremely hot climates or for towing. I'm not sure where to find 10W-50 or 20W-40 though. I haven't seen a manufacturer recommend 10W-40 for normal use in a while, like in the Subaru manual. Mostly I've had dealers say to use 10W-40 if the car starts using oil.

Also - don't EP additives cling to metal and protect during startup?

I've heard that lighter multi-weight oils can get to places heavier oils can't. Still - the engine is probably tolerant of a wide range of oil weights.

Primary reason is CAFE rules for gas mileage...

Older Subies had a recommendation on 5W-30 to avoid prolonged highway driving when using 5W-30, and recommended 10W-30 for warmer conditions (judging by my '90 owners' manual.) I think they were telling us the same thing Castrol used to post on their website: lighter oils are better for fuel economy, but don't protect as well as heavier oils under heavy use. That bit of info disappeared from Castrol's site several years ago--I don't know if it became obsolete, or politically incorrect?????

OTOH, a buddy bought a Ford Super Duty p/u with the V-10 a couple of years ago and has been running 5W-30 (Mobil 1) since break-in and he spends a lot of time in the desert, while we've been running 5W-30 in the g/f's Honda Civic since new (we live in a rather warm area of SoCal) and neither vehicle has shown any ill effects. But they don't have the

345k miles my Subie does, so it waits to be seen what the long term effects will be.

Rick C

Mobil 1 is a very different kind of oil, and their 5W-30 might be better under a load than a conventional 20W-50.

BTW - out of curiosity, is Ford now recommending their 5W-20 for use in their trucks? I've seen Mobil 1 0W-20 on a store shelves - the bottle says its an acceptable substitute for 5W-20.

Agreed on the fact it has some advantages over dino oil at the SAME viscosity level. Not sure on whether you can compare widely different viscosities between synthetic and dino oils, though.

I've heard that, too, but haven't asked anyone with a new Ford.

Personally, I think one's looking at shorter engine life in a truck (if it's used as a truck!) with that light a grade, but I'm guessing the engineers just might know more than I about the engine THEY designed! (Sorry, I'm not as smart as all the barstool engineers who know SO MUCH more than the guys who do it for a living...) Wonder if this might be a precursive move toward manufacturers advocating synthetics in "regular" cars/trucks (as opposed to Mobil 1 factory filled Vettes, Porsches, etc,) here in the US?

Rick

I've heard that, and while it's true heavier oils don't flow as well as lighter ones when cold, once the oil's up to operating temps, I doubt this idea holds much water. Ever drain hot straight 40 wt or even 50 wt oil from a car or motorcycle engine (back when these were recommended grades?) The stuff's pretty thin compared to when it's cold and I don't think it would have problems flowing thru a hot engine.

But, newer engines do have tighter tolerances, and in some cases, smaller oil galleries, so I might be off base. I'm sure part of the problem would be dependent on operating conditions: the guys in "cold country" face a whole different set of problems than we "desert rats" do! "Cold" to me is 40 deg F, while a guy in Buffalo, NY, right now is probably praying for the temps to get that "high!"

Rick

I believe the original Mobil 1 was a 5W-20 weight, and they were claiming that a thinner synthetic could protect better than the typical 10W-40 that people were using at the time.

Honda went to 5W-20 in the late 90's, even though some of their engines weren't redesigned. 0W-20 is the factory fill in their hybrids. They also mandated a switch to their proprietary manual transmission fluid (again - probably without a major redesign). My guess is that motor oil has advanced far enough that 5W-20 can properly protect an engine.

As for Ford - I was just curious if they were recommending this stuff across their entire offerings, i.e. - "You mean I'm supposed to put 5W-20 in my F-350?"

The theories I've heard aren't just about mass flow of oil. I heard some pseudo-scientific discussion about thinner multi-weight oils being able to temporarily "shear" and re-expand - enough to get into and lubricate modern rings better. I don't know - I just use 5W-30 year-round in the San Francisco Bay Area.

I'd like to know what European (and Japanese, or Aussie for that matter) owners' manuals have in them for oil recomendations - anyone monitoring this group? preferably in engines or car models avaible here in the states too - just to see if the viscosities are the same. I've read

20w-50 is quite often the weight of choice.

Carl

1 Lucky Texan

y_p_w wrote:

From what I've gathered sometimes scanning their newsgroups, some of the expensive German manufacturers (like BMW or Mercedes) have recommended 20W-50 oil even for their US divisions. I recall when Porsche switched to Mobil 1 as their factory fill, they said that any weight available in the US (0W-30, 5W-30, 10W-30, 15W-50) was acceptable, but that 5W-40 was used from the factory. The previous BMW M5/Z8 engine was only supposed to use Castrol RS 10W-60. These German cars now come with computers that calculate when a change is recommended based on driving conditions, and reports are that owners are getting at least 10K miles before they say to change.

The other thing we'd have to note is that the minimum API SL and GF-3 standards are likely way lower than the ACEA standards that are required in Europe. I also remember hearing how much "regular" motor oil costs in Europe, and it occurred to me that their standards likely required semi-synthetic or perhaps the latest generation (I think it's called hydrocracked) motor oil.

Here's a page that describes the Mercedes system in the M-Class:

BTW - Mobil is labelling Mobil 1 5W-40 as a "European Car Formula", as it's what Mercedes and Porsches use out of the factory.