Cetane and ULSD for older Yanmar engines - SailNet Community
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post #1 of 2 Old 11-12-2011 Thread Starter
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Question Cetane and ULSD for older Yanmar engines

40 Cetane rating is about the minimum most diesel engines can run on efficiently..I'm sure there are some diesel engines can run on lower ratings..but 40 is suppose to be the minimum standard. From my readings on the BoatUS site there is a winter blend that helps alleviate cold starting issues.

Since December of 2010 Ultra Low Sulfur Diesel fuel (15 ppm)has been mandated through out the US as compared to the older Low Sulfur dispensed diesel of 500ppm.

I read somewhere that older Yanmar engines, earlier than 1997, required a minimum of 500 ppm sulfur as lubricity requirement and also that there is no guarantee that at the fuel pump we are getting the minimum 40 Cetane.

Yes there are additives..but the BoatUS report further stated: "...be aware that an independent study of 19 additives sold to improve an engine's Cetane rating found that five had no significant effect on the fuel's cetane rating and four additives significantly lowered cetane content." There was no mention as to which additives where used in this study...

So I ask of older Yanmar owners what additives have been successful for improving Cetane and lubricity??
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post #2 of 2 Old 11-12-2011
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There was a lot of concern when ULSD first came into being because of the lower lubricity. The only problems that I have observed were more leaking seals on some older powerstroke engines found in the ford diesel pickups. When it first came out, there seemed to be a few more problems with gelling but the new trucks also came with fuel coolers which made this a bigger issue as well.

Regarding lubricity, the sulfur itself provides no additional lubrication. The process of removing the sulfur also happens to lower the lubrication but it is only a function of the process. There are standards for lubrication in different fuels which are tested with a test where they essentially scratch a surface. It is true that ULSD provides slightly lower lubrication than LSD but it still is acceptable. In most fuel pumps, lubrication is provided by the engine oil and not the fuel, this was one of the major problems for the dreaded bosch vp44 injection pumps which lubricated with fuel (not found on yanmars). It is unlikely that running ULSD without any additives will shorten the life of the engine, something else is going to determine it.

Cetane does directly relate to how the fuel burns but ULSD has a high enough cetane rating for any engine out there, especially the older ones. Minimum cetane on highway fuel is regulated at 42 anyways. The older engines tend to be much more tolerant of poor fuel quality and will run just fine on much poorer quality fuel.

Regarding winter blending, this has changed a lot over the years. It used to be that #1 oil (similar to kero) was blended in with the #2 in the winter to prevent gelling. When everything switched over to ULSD, they went away from blending for the most part and started using fuel additives instead. Very few people use their boats at time when winter fuel is available. If you use your boat in extremely cold climates and the area where the fuel tank is gets very cold <0F, then you might think about a fuel additive to prevent gelling such as powerservice white.

In short, while ULSD is probably marginally worse for old engines, there are much more important things to worry about. Keeping your fuel tanks clean and algae free, changing your fuel filters and doing other general maintenance properly will do much more for prolonging the life of your engine than messing around with additives.
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