Oil, why not follow owner's manual recommendation?

I am reading a 2010 Subaru owner's manual, it shows a chart of recommended engine oil viscosities for a given ambient temperature range. For cars operating in temps above -5 degrees Fahrenheit it recommends using 10w-30, 10w-40, or 10w-50 oils.

About 90% of US drivers fall into this category,

99.9% of the time.

Why is it that so many people decide not to follow this recommendations and pour oils of 5w-30, or

5w-40 viscosities?

The manual shows a second chart where 5w-30, and 5w-40 are shown along the entire temperature spectrum, from less than -20 to above 100 degrees F. Meaning these oils are also permissable, but they are not a perfect match!

I do not understand the logic behind the use of these thinner oils. Do people no longer care about their engines, and prefer a thinner oil for better fuel efficiency alone. Why then stop at 5w-30, and not pour 0w-30, or 0w-20, or even thinner (0w-10 will soon be available).

Basia

Reply to
abjjkst
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This is a 2010 Subaru Legacy owner's manual.

Basia

Reply to
abjjkst

The damage from 10w oil that does not flow on a rare day when your claimed 10% of the population in snowbelt drives their cars at -5F will outstrip the wear protection vs 5w during warmer times.

FWIW mazda specifies 5w-20 for rx-8 and I would not be surprised if some morons ruined their wenkels with 10w-40. I suppose they would've been better with 0w-20 you seem to have so much disdain for.

If I were in snowbelt or were a california skler type I'd stay away from 10w semisynthetic on a late model car in snowbelt Sept through May. If you live in redneck states or run straight synthetic indeed 10w could work just fine.

I run 75w-80 in the rear diff of my ancient RWD beater. And that (dino) gear oil looks a lot like motor oil viscosity wise :^)

My car mechanic was delighted to pump this fluid: e-a-s-y

Reply to
AD

My '94 Honda Accord Owner's Manual recommends 5W-30 oil, regardless of the season.

Reply to
Cameo

OK that makes sens as a precaution, in autumn, winter time, ...but why pour this thin stuff year round in places like Florida, Texas, California.

Are people that desperate for a miniscule gain in fuel economy?

I live in the Sierras, in Reno, Nevada and since new have always used nothing but synthetic 15w-50 in my 2000 Impreza, ...other cars also get thicker oil

15w-40, or 10w-40.

We have occasional cold spells here, too. The engine in the Impreza is supertight, almost like new despite

80k miles. It gets good protection at higher rpms. I drive in mountains frequently. I cannot imagine putting anything thiner tan 10w-30 here no matter what. 5w-30, 5w-40, this stuff is basically for arctic conditions. Why do people insist on it? I cannot make much sense of it (Wankels aside).

Basia

Reply to
abjjkst

Honda is supposedly working on new oil viscosity recommendation of 0w-10 !!!

Their chief chemist says the new upcoming engines are, or will be designed to handle such. No word on longevity/durability. I think they presume the public will believe it to be unaffected (?).

But how?

With such thin oil almost every start will be a cold start!

How else?

One of the reasons to use a somewhat thicker oil is to have it cling better to internals and prevent cold starts. This 0w-10 stuff is bound to drain into the pan entirely in about an hour or so depending on ambient temperature. A 10w-30 oil in 100 degree plus weather drains nearly completely into the pan in just several hours, resulting in a complete cold start!

I would never put anything thinner than 10w-30 in my Subies engine, despite the fact that as horizontal engines they don't drain oil completely into the pan.

Basia

Reply to
abjjkst

.

I forgot to add, depending on how frequently you drive you want an oil that cover the internals until you start the engine next time.

If it is a daily driver, and in cool weather, a 5w-30 might do the job, i.e. not drain into the pan entirely in 12 hours or so. If the car is driven only a few days a week, a 10w-30, or 15w-40 is better. During hot weather a 20w-50 is much better. If the car is driven ocassionally, say once or twice a month, its a good idea to use a straight 30. It'll cling to parts for a long time preventing rust and a complet cold start even after days.

A complete cold start is when the engine gets worn most.

Basia

Reply to
abjjkst

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I think tighter clearances demand lower viscosities. Perhaps with CAD, modern alloys and modern machining, they can achieve design parameters that work better with lower viscosities.

Reply to
1 Lucky Texan

I don't understand what your point is about using a thinner oil if the manual states 5w is fine for -20 to +100F. You just answered your own question. Personally, there's no way I'm having a 10w oil in when it is anywhere below 20F. I can certainly hear the difference on start-up For your question about 0w-30 or 0w-20, the manual does not state to use it, so....why would you? Moot point

Reply to
John

You shouldn't. In FL run 10w-30 year-round, here in MA, we go 5w-30 for Dec-Mar and 10w-30 Apr-Nov BTW, our Honda Odyssey calls for 0w-20 YEAR ROUND!

Reply to
John

The specified clearances have not changed any significant amount in the last 30 years.

Reply to
clare

I have ALWAYS used a minimum of base 10w oils in all my cars here in Ontario Canada. My current vehicle uses 10W40 Synthetic - but everything else I've ever owned used 10W40 standard oil in cold weather and 20W50 in summer.

Reply to
clare

But the 0W20 is synthetic, which behaves differently.

Reply to
clare

You are very logical, but the manual shows two charts, one specifies three viscosity grades which are progressively thicker and aligned with rising temperatures, and looks something like this:

-5F ----->10w-30, 10w-40, 10w-50

...the other shows only two thinner grades along the entire temperature spectrum, and looks like this:

-20F 100F

Why two different recommendations?

Both 5w-40, and 10w-50 cannot protect exactly the same way. One must be better/worse in some aspects than the other.

What is the point of recommending two different grades for same operating conditions?????

To stir up confusion?

Or is it perhaps because manufacturers are being pushed into recommending fuel conserving oil grades, but cannot easily abandon the idea that slightly thicker oils protect the machinery far better?

I suspect that is exactly the case!

Basia

Reply to
abjjkst

They may be a bit tighter nowadays, but not by very much. The Subie 2.5L engine specifications I think are the same for more than a decade.

But, once you accept the arguments for thinner oil, and start using a ultra-thin oil that does little or nothing to prevent cold starts (because it drains into the pan too fast),

...the logic changes into one favoring progressively thinner oils, as these flow better and the pump can push them faster to were the oil needs to be.

Basia

Reply to
abjjkst

They may be a bit tighter nowadays, but not by very much. The Subie 2.5L engine specifications I think are the same for more than a decade.

But, once you accept the arguments for thinner oil (better cooling, fuel efficiency) and start using a ultra-thin oil that does little or nothing to prevent cold starts (because it drains into the pan too fast),

...the logic changes into one favoring progressively thinner oils, as these flow better and the pump can push them faster to were the oil needs to be.

Basia

Reply to
abjjkst

Asside from tight tolerances, I thought the idea of a thinner oil, especially at colder temps, was to get the flow moving more freely vs. the thicker weight possibly not flowing as quickly and thus causing limited oil starvation on startup.

Reply to
John

The "theory" is that thin oil pumps faster, so the "dry start" doesn't last as long. Personally, I'm not sure I buy it. I still like an oil with a bit of body to it.

Reply to
clare

Although it may be less of an issue for our boxer engines, the greater use of anti-drainback valves in oil filters may figure into this discussion as well. At least, I think that's a somewhat recent development/becoming more common. anyone?

Reply to
1 Lucky Texan

I occasionally read rumors of owner's manuals in other countries, without CAFE-type regulations, recommending higher vis. oil for the same engines sold in the States where the 5w-w'ever range is recommended. Any way to confirm this?

Reply to
1 Lucky Texan

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