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Old 16-01-2017, 06:08   #31
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

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Ahoy sailors,

Hopefully a simple question for those who know what this is all about. I am about to change oil for my 3GM30F Yanmar and was looking in what to use. I am not sure what all those numbers mean on oils

Is Rotella T6 5W-40 Full Synthetic Diesel good for it? I read in the forums that full synthetic might be an overkill for old engines but I don't mind an overkill as long as it doesn't hurt the engine.

I would rather go with a robust oil and pay a bit extra than have doubts.

Any recommendations?

P.S. If it matters at all, boat is in San Francisco Bay.
For more information on oil for yacht engines checkout this UK website.
Oil for yacht engines
Cheers
Cabo Jim
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Old 16-01-2017, 10:39   #32
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

The older Yanmars recommend straight 30W oil. I have used Shell Rotella T straight grade oil for over 20 years/2400 hours in my 3GM30F. If you change your engine oil every 100 hours, I would think the difference in using full synthetic vs regular oil might be a moot point. I will continue regular oil changes and straight grade non-synthetic oils. Good luck and safe sailing.
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Old 16-01-2017, 11:03   #33
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

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Originally Posted by rognvald View Post
The older Yanmars recommend straight 30W oil. I have used Shell Rotella T straight grade oil for over 20 years/2400 hours in my 3GM30F. If you change your engine oil every 100 hours, I would think the difference in using full synthetic vs regular oil might be a moot point. I will continue regular oil changes and straight grade non-synthetic oils. Good luck and safe sailing.
I would agree! I would like to hear from some one that does oil analysis. I doubt regularly change oil loses it lubricating properties it gets contaminated.
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Old 16-01-2017, 11:23   #34
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

Simple answer is - yes. Rotella T6 is magic oil. It's not cheap, but it will last longer and will give longer life to the engine. Unless engine is very old, worn out and needs repair. But that's another case, neither oil will help.
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Old 16-01-2017, 11:25   #35
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

Rotella. The best synthetics have the lowest scarring and wear factors; it is a no brainer choosing them.

I use Amsoil in two cars exclusively. One had 160k miles on it when I bought it, the second 129k. The former now has 200k miles on it, the latter 144k miles.

An engine, gas or diesel, would have to have a pile of crud build up to make it an issue.
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Old 16-01-2017, 13:54   #36
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

T6 is excellent oil, it will not hurt your engine.
Our little Non Turbo Diesels are very easy on oil, do not run hot etc.
Oil in our motors does not break down, it gets loaded with soot, that is why we change it.
I run T6 in all my vehicles, and used to run it in my boat, but have switched to straight 30 for ease of finding it and the T6 is just not needed, but it will certainly not do any harm even though there is at least one expert that says it will cause cylinder glazing
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Old 17-01-2017, 21:08   #37
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

In your climate, I'd stick with the recommended 15W 40. I now use John Deere Plus 50, in a 15W-40 grade, which enables extended change interval, because of the additive package therein. That way, if I'm in a remote area, or out at sea, I can run past the regular change interval without harm.
Synthetics may result in a bit of oil consumption, after switching, but the engines usually settle down after one change. It costs a lot more, but won't do any harm.
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Old 17-01-2017, 22:15   #38
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

Shell Rotella is a sort of benchmark of oils for diesels. I use Amsoil which is arguably a better oil (Amsoil invented the synthetic oil). But between Shell, Mobile, Royal Purple and Amsoil they are all good choices for gas or diesels.
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Old 22-01-2017, 09:54   #39
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

For what its worth. A mechanic friend of mine suggest using synthetic for long term storage. States it is less acidic and doesn't absorb moisture. But I have no experience with this. Just saying.
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Old 22-01-2017, 11:19   #40
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

Thanks to Jim Cabo for his earlier link. It was eye opening.

Oil for yacht engines

Especially this: "What needs to be remembered is that lubricant development keeps in step with power requirements in the automotive field. Oil temperature, stress and change intervals in modern diesel cars and trucks bear little resemblance to the equivalents of 20 years ago. Yacht engine operation, however, has not changed in the slightest."

I had always believed that the a higher "C" code was always better. But this goes on to say that the newest oil standards may not be a good match for long periods of running at mid-range RPM's at one throttle setting (like on many boats). Synthetics are especially problamatic in this usage profile.

My five year old Yanmar 4Jh4-HTE turbo specificies CD, CF, CF-4, or CI-4 oil (or higher, they say..) When my engine was designed for the 25 year old CD standard, oil was a very different thing. I can't find a widely available 15W-40 oil now that is lower than CJ-4.

When the engine was designed for the CD oil standard of 25 years ago the engineers had no way to guess what today's CK-4 standard would be. Does anyone (either Yanmar or the oil manufacturer) fully test older marine engines in realistic operating situations to see if the claim oil backward compatibility is accurate for these new oils?

I doubt it.
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Old 22-01-2017, 11:45   #41
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

So, how to heat it up, or just wait till it gets dropped innthe water?

Sophia:
If you are trying to pump the old oil out thru the dipstick oil, you won't have much success at cold temps. If you have access to shore power, put a small wattage (60W) incandescent light bulb (a trouble light, bulb in a cage) low in the engine compartment overnight to warm the block & oil. Otherwise, wait until spring. Best to change oil in the fall before winter storage.
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Old 22-01-2017, 13:23   #42
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

Curious Carl....how are synthetics problematic for older design diesels or diesels that run at low loads for long periods of time.

The web site suggests HIGH TBN concentrations in oil.....what is considered high....also the Shell engineer "agrees" some ingredients cause premature wear,,,,,,did they elaborate?

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Old 22-01-2017, 14:09   #43
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

Find it hard to fathom how a "modern" synthetic oil could cause premature wear in an older motor.

The way oil "insulates" metal to metal surfaces under load - film strength, viscosity, flow rate at wider ranges of specified temperatures, keeps particles in suspension have all improved.

Filtration technologies have improved.

The detergents in oils that remove (and then prevent) sludge, carbon and varnish build up really should not be an issue unless the oil and filter are not changed at proper interval.

So unless there is something in these oils that actually attacks the metals they come in contact with it does not sound logical.

An engine usually run at certain rpm ranges for long periods should be even less susceptible to wear, provided oil flow and pressure is adequate or better in those rpm ranges. This is why vehicles driven and accumilate highway miles usually last a lot longer than those used in cities and urban areas.

Cold starts, idle rpms where oil pressure and flow are reduced and high rpm with insufficient oil flow (such as right after a cold temperature start and oil with a low cold flow rate) are what cause most engine wear. It doesn't matter whether the engine is driving wheels or a propeller.

I have run a truck with a late 1960s motor that had already been round the clock at least once when I bought it, and gone on to put another 100k on it over about 10 years with "modern" oil with no problems at all. It didn't smoke or anything else when I sold it.
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Old 22-01-2017, 14:32   #44
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

I also have a serious question as to how one 30 hour stint at steady RPM's caused engine failure....
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Old 22-01-2017, 14:46   #45
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Re: Shell Rotella T6 5W-40 Full Synthetic Diesel for Yanmar 3GM30F

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I also have a serious question as to how one 30 hour stint at steady RPM's caused engine failure....
It has nothing to do with the oil. Prolong running at one RPM can cause wear to one height on the cylinder wall and cause ring damage when RPM is increased. It is difficult the believe the minute difference in stoke is there but apparently is. It can only be a RCH an that is a scientific measurement.
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