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Old 25-01-2014, 17:10   #16
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Re: Oil For New Yanmar 3YM20's

Originally Posted by noelex 77 View Post
There is a good article here:

Oil for yacht engines

The most important thing is to change the oil regularly.
There is an argument that high performance oils (full synthetic) are not beneficial and may even be harmful for our yacht engines.
It is difficult to evaluate these claims, but a good quality mineral oil of the right grade, changed frequently seems the best option.
That link makes some seemingly contradictory arguments.

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.
My assumption is that the OP's new engines are for moving the boat, not as an auxiliary. The link does state that the latest diesel rated oils have a lower TBN because of ULSD which I have seen in my UOA. So he seems to be arguing that high TBN oils are bad, yet the newer rate oils do not have high TBN.

My truck engines have been turbo charged by my tractor is not. I would think the tractor engine runs more like a boat engine since I set the throttle and seldom change the RPMs, unlike the truck engine which has RPM all over the place.

One thing I have learned via UOA is to avoid "idling" since it leads to fuel in the oil. I have hit this on my truck engine when I had to travel a route with heavy stop and go traffic as well as my tractor engine where I was running the RPMs at a speed that worked well for the work I was doing. I would run the tractor at 1600ish RPM but after getting fuel in the oil, I kicked up the RPMs to 1800-2000 which solved the fuel in oil problem. The fuel percentage in the oil was never bad enough to hurt the engine, thankfully, but I sure did not want the fuel in the oil. My route with the truck changed so I avoided the extended idling.

Again, I run synthetic's because I run my oil longer than the manual states, for better cold weather starts, and better MPG. Not sure how relevant that would be for a boat engine.

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Old 25-01-2014, 17:32   #17
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Re: Oil For New Yanmar 3YM20's

Thanks for all the thoughtful replies...... I made the decision to use Rotella T 15W-40 because we are headed south as soon as this cat shakes down.

here's my builders log: F-44SC Catamaran

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Old 29-06-2015, 09:43   #18
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Re: Oil For New Yanmar 3YM20's

Hi - resurrecting this thread, as I have the same question. However, the service manual for the 3ym20 specifically states: "Never use API service category CG-4 or CH-4 oils".

The Rotella 15-40 says it is CH-4.

What gives? even the Yanmar oil 15-40 is 'in violation' of this??

supposedly it will create excessive wear on the lifters.

does any of that make sense?
Thanks for any info, David - Tampa
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Old 29-06-2015, 11:51   #19
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Re: Oil For New Yanmar 3YM20's

Over in another forum, someone said that Mack Boring said that:

Their response was that any oil with CF rating or better was OK to use with the 3YM30. Acording to the service person I talked to, the reason for the blurb about not using CG-4 or CH-4 was because Yanmar hadn't tested these type oils in their industrial engines a few years ago when they first came out with the CG-4,CH-4 ratings. They just inserted this caution in all their industrial manuals until they could test the oils with the ratings. According to the service person, the cautionary statement is obsolete now but hasn't been removed from their manuals .

Internet hearsay, but sounds about right

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