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Old 24-07-2013, 09:58   #1
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Oil Spec Question

Hi

In purchasing oil for my Yanmar 4LH the only spec I could get locally is 15w40. Am I right in assuming that this is somewhere between 20w40 and 10w30? These are the grades shown in my engine manual as suitable.

For use in temperate conditions.

Thanks.
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Old 24-07-2013, 10:12   #2
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Re: Oil Spec Question

Motor oil - Wikipedia, the free encyclopedia
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Old 24-07-2013, 10:20   #3
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Re: Oil Spec Question

15w40 is the same viscosity when hot as the 20w40, but should provide better cold starts as it is slightly thinner when cold. Should be ideally suited to your engine. Oil technology has advanced, that is all.

I usually use Shell Rotella T although plenty of people seem to like the Chevron Delo line too.

What brand did you buy?
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Old 24-07-2013, 10:53   #4
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Re: Oil Spec Question

Basically the numbers give an idea of viscosity at different temperatures. The 'W' stands for 'weight'. A 15W40 oil will have the viscosity of monograde 15W oil when cold and the viscosity of monograde 40W oil when hot. If your engine manufacturer recommends 10W40 or 20W40 - presumably for cold and hot climates respectively - then 15W40 will work fine.

The most important number is the top one as this determines the viscosity of the oil when your engine is up to temperature. A viscous oil will form a good protective film over engine parts but it won't penetrate very well. Conversely a thinner (lower weight) oil will penetrate well but won't form as good a protective coating over parts.
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Old 24-07-2013, 15:58   #5
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Re: Oil Spec Question

thanks
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Old 24-07-2013, 16:28   #6
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Quote:
Originally Posted by DefinitelyMe View Post
Basically the numbers give an idea of viscosity at different temperatures. The 'W' stands for 'weight .
Actually stands for " Winter"
It indicates "winter" or cold start viscosity
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Old 24-07-2013, 17:27   #7
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Re: Oil Spec Question

Some engines ask for grade 'not less than X'. I think this applies esp when turbo present. Also, not all engines are supposed to use synthetic oil.

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Old 08-08-2013, 13:39   #8
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Re: Oil Spec Question

Also, check the SAE rating on the oil. This is specified as CA/SA rating, with S ratings for spark (gasoline) engines and C rating for compression (diesel) engines. Anything lower than CD is obsolete. The newer and fancier the engine (turbos, etc.) are more picky about the ratings and require better than CD. The last Ursa oil I bought was CJ-4, I think.
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Old 08-08-2013, 15:09   #9
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Re: Oil Spec Question

Can one be too good?

I mean, if I have a very old diesel engine, can I hurt it anyhow using an ultra modern HQ oil in it?

barnakiel
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Old 08-08-2013, 15:16   #10
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Re: Oil Spec Question

If you perform oil and oil filter changes using the "latest HQ oil" and do so at the recommended intervals (usually 100 hour or annual) you will not harm any motor - no matter how old it is.

Charles
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Old 08-08-2013, 15:27   #11
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Re: Oil Spec Question

Quote:
Originally Posted by barnakiel View Post
Can one be too good?

I mean, if I have a very old diesel engine, can I hurt it anyhow using an ultra modern HQ oil in it?

barnakiel
Yes, you can hurt it!

Read this:

Oil for yacht engines

The author is a sailor and former petroleum engineer.

Basically, "high" grade motor oils designed for hot running, high RPM, high specific output car engines can be very destructive to cold-running, low-speed yacht engines.

It's a real problem because Yanmar engines are designed for CD grade oil, which is no longer available in most places. I have been using Yanmar's own overpriced oil, in order to avoid this problem.

"Over-Specification.

Yacht auxiliary engines generally run for short periods, at lower temperatures than any other duty, and typically in the lower half of their rev range. From a lubricant point of view this is a very undemanding duty, accounting for their low API requirement. Combustion temperatures never reach levels at which a high-performance lubricant can be effective, so the overall chemistry in this area is not neutral but alkaline (basic). There is a great deal of evidence to show that use of an oil with a TBN that is too high for the duty can lead to several problems, particularly high wear rates of cylinder bores. The effect of high TBN engine oils in accelerating wear rates is well known. Burning high TBN oils may generate excessive deposits on the piston crown. As the piston tilts when moving up and down these deposits become compressed and will form a very hard and abrasive layer, causing excessive wear, mainly in the bore."


From the Vyv Cox article linked above. Emphasis added.
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Old 08-08-2013, 16:10   #12
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Re: Oil Spec Question

(corrected)

OK. I get the picture.

OK. I read the article now. I understand. Many thanks!

I have learned something today.

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Old 08-08-2013, 17:00   #13
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Re: Oil Spec Question

The article is poorly referenced - in fact there are no references to support the suggestion that higher API numbered oils lead to accelerated bore wear.

The article does make one thing clear: The concerns Cox expresses seem to be confined to synthetics (possibly synthetic blends the article does not say) not to plain vanilla oil.

So yes - avoid synthetics in order to maintain acceptable bore wear rate.

Just remember - no matter the oil API rating - there are other very effective ways to ruin ring to bore sealing.

Charles
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