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Old 12-08-2015, 08:47 AM   #1
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Yanmar - Mobil 1 Synthetic

I'm the new owner of a Mainship with Yanmar 6LYA-STP, 370HP. The owner's manual says I should use 15W-40 weight oil. The previous owner used 15W-50 Mobil 1 synthetic, which does not come in a 40 weight. Stick with the 50?
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Old 12-08-2015, 09:15 AM   #2
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15W-40msynthetic diesel rated is available from many suppliers including Shell.


Why not use what the maker directs?
https://www.google.com/search?q=15w-...sel+oil+15w-40
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Old 12-08-2015, 09:36 AM   #3
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I'd use the PO's oil.

Mobile 1 synthetic if it was/is formulated for diesel engines. The 15W50 viscosity is fine. Better almost certianly. Check w Yanmar to be sure. They may not have had 15W50 when the engine was made. They are a better source of information on what to do w a Yanmar than we are. Nice of you to ask though.
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Old 12-08-2015, 09:51 AM   #4
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Mobil 1 15W50 is S rated for gasoline engines. You need to use a C rated oil which is formulated for diesel engines. If you want to stay with a synthetic I suggest Shell Rotella T6 5W-40 synthetic. If you don't want to stay with a synthetic then any CJ rated 15W-40 will do. Good brands are Shell Rotella T, Chevron Delo 400, Texaco Ursa, etc.
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Old 12-08-2015, 10:06 AM   #5
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Why use a synthetic oil at all?


Synthetics have two primary advantages over a petroleum based oil: they have somewhat better lubricity compared with petroleum based multi grades and they don't oxidize as badly over time so they maintain their properties over a long period.


But petroleum based oils do just fine in the lubricity department and I suspect that you will never see any benefit during the life of the engine. Marine diesels don't wear out usually and never due to poor lubricity. Overloading, yes!


Secondly even ignoring manufacturer's recommendations, oil in diesel engines need to be changed to remove soot, fuel and replace lost additives, none of which is helped by having a synthetic. Sure big fleet operators test their oil and change it when those values get out of whack, but does a single boat operator want to do that, especially if it goes against the manufacturer's recommendations? So the low oxidation properties of synthetics is lost if you have to change the oil anyway.


But if you must use a synthetic I suspect there is no practical difference in Mobil 1's 15W50 and a petroleum based 15W40.


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Old 12-08-2015, 10:44 AM   #6
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The downside for synthetic in a recreational boat is hard to overcome.

Syntheic scrapes off and drains better , so it improves the mileage a tiny bit.

The hassle is they drain really well so the engine can get exposed to internal rust , and even dryer than normal cold starts.

Use the car or truck a lot , they do work, esp for ultra high loads in a high performance engine.

Use the boat once a month or so, there is no advantage.

On layup there is extra work required to seal the engine air tight.
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Old 12-08-2015, 10:49 AM   #7
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Not sure if it is still true of today, but back some Yanmar did NOT recommend synthetic oils.
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Old 12-08-2015, 10:53 AM   #8
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I supported the synthetic oil and the MV only because the engine in question is a high output turbocharged engine presumably making lots of heat in the turbo.
That would be the only reason it would need ..
A. Synthetic oil (lube)
B. Multiviscosity ratings w MV additives.

Otherwise straight 30 or 40W oil would be best.

The only really significant advantage to synthetic oil is it's ability to perform well at very high temperatures. Synthetic is a lot better at dealing w heat. But the only place you'd find so much heat that the usual mineral (dino) oil may have trouble dealing w it is in high output turbocharged engines. No others.

But w the OP if he intended to run the engines hard I'd stick w the syn 15W50. I see he's a fisherman (sports) and most of them from what I read run really fast out to the fishing grounds.
If the OP was to run that boat more sedately .. say about 15 knots .. then I'd run 15w40 dino oil.

Just my opinion and in this case I'd call Yanmar.
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Old 12-08-2015, 11:29 AM   #9
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Quote:
Originally Posted by TDunn View Post
Mobil 1 15W50 is S rated for gasoline engines. You need to use a C rated oil which is formulated for diesel engines. If you want to stay with a synthetic I suggest Shell Rotella T6 5W-40 synthetic. If you don't want to stay with a synthetic then any CJ rated 15W-40 will do. Good brands are Shell Rotella T, Chevron Delo 400, Texaco Ursa, etc.
According to the product data sheet, Mobil 1 15W-50 meets the quality level of API CF.

Mobil 1™ 15W-50
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Old 12-08-2015, 11:49 AM   #10
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Use any diesel rated oil you want.
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Old 12-08-2015, 11:58 AM   #11
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According to the product data sheet, Mobil 1 15W-50 meets the quality level of API CF.

Mobil 1„ 15W-50
I only found the SM rating when I looked. I note that your reference says "meets the requirements for CF", but doesn't say it is CF rated. That said CF is an old rating and CJ would be much better. If the engine is 1998 or newer the manufacturer likely called for CH or higher rating oil. Here is the info for CF rated oil.

CF Obsolete Service typical of indirect-injection diesel engines and other diesel engines that use a broad range of fuel types, including those using fuel with high sulfur content; for example, over 0.5% wt. Effective control of piston deposits, wear and copper-containing bearing corrosion is essential for these engines, which may be naturally aspirated, turbocharged or supercharged. Oils designated for this service have been in existence since 1994 and may be used when API Service Category CD is recommended.

However, the statement of using C versus S rated oils stands.
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Old 12-08-2015, 12:11 PM   #12
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Quote:
Originally Posted by TDunn View Post
I only found the SM rating when I looked. I note that your reference says "meets the requirements for CF", but doesn't say it is CF rated. That said CF is an old rating and CJ would be much better. If the engine is 1998 or newer the manufacturer likely called for CH or higher rating oil. Here is the info for CF rated oil.

CF Obsolete Service typical of indirect-injection diesel engines and other diesel engines that use a broad range of fuel types, including those using fuel with high sulfur content; for example, over 0.5% wt. Effective control of piston deposits, wear and copper-containing bearing corrosion is essential for these engines, which may be naturally aspirated, turbocharged or supercharged. Oils designated for this service have been in existence since 1994 and may be used when API Service Category CD is recommended.

However, the statement of using C versus S rated oils stands.
I looked at the data sheet because I was wondering if using that product would result in harm to the engine. It convinced me it was unlikely to result in engine damage. Would I use it? No, I would stick to an oil that was designed for diesel engines (C service).
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Old 12-08-2015, 01:22 PM   #13
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Generators and engines have turbos that can cook dino oil if not allowed to cool down prior to shut down. Syn oils are supposed to be better at that.


I don't ever remember reading about an lubrication caused failure of a boat engine. You could probably use the cheapest Wallyworld lube oil without any problems if you don't want to follow the makers advice, but why?
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Old 12-08-2015, 05:26 PM   #14
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I spent many years in the "OIL" industry and I would prefer to change my petroleum based oil and filters twice for the same price of synthetic once .

Sorry no more comment
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Old 12-08-2015, 05:35 PM   #15
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Mobil also makes the mobil delvac which is a diesel specific oil. I havent priced it, but knowing mobil it probably costs a lot more than shells rotella T6 and probably not much better performance wise.
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Old 12-08-2015, 06:00 PM   #16
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50wt is some really thick stuff. No way I would want to spend my fuel dollars churning honey in the sump. Use what the mfr recommends.
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Old 12-08-2015, 07:11 PM   #17
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Quote:
Originally Posted by djmarchand View Post
Why use a synthetic oil at all?

Synthetics have two primary advantages over a petroleum based oil: they have somewhat better lubricity compared with petroleum based multi grades and they don't oxidize as badly over time so they maintain their properties over a long period.

But petroleum based oils do just fine in the lubricity department and I suspect that you will never see any benefit during the life of the engine. Marine diesels don't wear out usually and never due to poor lubricity. Overloading, yes!

Secondly even ignoring manufacturer's recommendations, oil in diesel engines need to be changed to remove soot, fuel and replace lost additives, none of which is helped by having a synthetic. Sure big fleet operators test their oil and change it when those values get out of whack, but does a single boat operator want to do that, especially if it goes against the manufacturer's recommendations? So the low oxidation properties of synthetics is lost if you have to change the oil anyway.

But if you must use a synthetic I suspect there is no practical difference in Mobil 1's 15W50 and a petroleum based 15W40.

David
No practical difference between a 40 grade and a 50 grade oil? Then why make two different grades? The difference is the viscosity at operating temperature. Engines are designed to use oils of a specific grade. Using a 40 grade oil in an engine designed to use a 30 grade is just the wrong way to go. Some folks believe that a higher grade oil is better to use in higher ambient temperatures because it stays thicker. Yes, at operating temperature it does stay thicker, thicker than what the engine was designed for. Remember, regardless of the ambient temperature, an engine, barring extremes boaters do not see, will run at its design temperature as regulated by the thermostat. That means the oil will be at the same viscosity at operating temperature REGARDLESS of the ambient temperature. Hence, using the 40 grade oil is not good. At operating temperature, the 40 grade will be too thick. And don't quote me Bob Smith. He is not a petroleum engineer. This is science folks.
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Old 12-08-2015, 07:23 PM   #18
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Quote:
Originally Posted by FF View Post
The downside for synthetic in a recreational boat is hard to overcome.

Syntheic scrapes off and drains better , so it improves the mileage a tiny bit.

The hassle is they drain really well so the engine can get exposed to internal rust , and even dryer than normal cold starts.

Use the car or truck a lot , they do work, esp for ultra high loads in a high performance engine.

Use the boat once a month or so, there is no advantage.

On layup there is extra work required to seal the engine air tight.
Sorry to disagree, FF, but you have it 180 degrees off course on the properties of synthetic oil. You say that synthetics drain really well and leaving metal surfaces open to rust. Wrong. Wrong. Wrong. It is the dino oil that drains away and leaves surfaces dry. In fact, synthetics do just the opposite, they cling to metal surfaces, which is one the benefits synthetics offer that dino oils do not. Extra work to seal the engine? Poppycock! From where does this nonsense come?
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Old 12-08-2015, 07:38 PM   #19
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catalinajack,
Thank you very much for clearing up this sticky subject.

gaston wrote;
"I spent many years in the "OIL" industry and I would prefer to change my petroleum based oil and filters twice for the same price of synthetic once ." Exactly.

ski,
50W as in 15W50? That's that the 15W50 oil has the viscosity of 50W oil at about 200 degrees ...... and at 200 degrees it's not thick at all. More like thin.
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Old 12-08-2015, 08:01 PM   #20
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I'm the new owner of a Mainship with Yanmar 6LYA-STP, 370HP. The owner's manual says I should use 15W-40 weight oil. The previous owner used 15W-50 Mobil 1 synthetic, which does not come in a 40 weight. Stick with the 50?
I would stick with a 0Wx40, 5Wx40 or 15Wx40 oil.

My guess is that the previous owner could not find 15Wx40 oil and bought 15Wx50 oil instead. I have been buying oil for my truck and tractor from my JD dealer for the last few years, believe it or not, they had the best price most of the time. Last oil change I did not have time to get to the JD dealer so I looked at the local auto parts store and their price for Shell 0Wx40 diesel rated oil was pretty good and on sale.

Since it has been years since I bought oil from an auto parts store for my diesel, I was shocked at all of different motor oil weights now available. There were plenty of oils that appeared to be diesel oils, but on reading the labels, they were gas only. The diesel rated oil was on a completely different aisle and not near the gas motor oils. I suspect the previous owner missed the diesel rated oil...

Years ago, a big name motor oil company said they had a diesel rated oil and many people were paying top dollar for that oil for use in tractors and trucks. The company said the oil was diesel rated but the jug was not labeled as diesel rated. I think the company did not want to be pay to get the oil rated. Now, I would guess the oil was ok but given there are plenty of good oils out there that ARE rated for diesels, that is what I used then and now.

Use a diesel rated 15Wx40 oil at a minimum since that is what the manual says. I use synthetics for a variety of reasons but you can't go wrong using what the manual specifies and changing the oil per said manual.

Later,
Dan
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