PS Advisor July 2009 Issue

PS Advisor: Synthetics for Marine Diesels?

Extended-life oils offer little to no benefit for most.

I recently read that synthetic oils, such as Mobil 1 have been approved for diesel engines. Do you have anyone with knowledge or opinion about their use in marine diesels? I have used Mobil 1 10-30 in my BMW D-50 diesel for the past nine years, and it seems to have worked out well, including during four trans-Atlantic crossings. We still have good compression and do not smoke or burn oil. Also, it is

Synthetic Oils for Diesel Engines
While Mobil 1 produces synthetic oils for diesel engines, makers of small marine diesels specify conventional API-rated oils.
readily available in the Med.

 

Lloyd Hamilton
River Gull, S&S/Lyman Morse-built Seguin 46 sloop
Grand View-on-Hudson, N.Y.

Mobil 1 extended performance oils for automobiles are advertised as providing engine protection and performance at extended intervals of up to 15,000 miles or one year, whichever comes first. Its 5W-40 Turbo Diesel Truck oil meets American Petroleum Institute (API) standards for diesel truck lubrication, and except for the price ($5-$8 per quart, or three times the price of conventional multi-grade oil), would seem to be an attractive option for ocean voyagers who might otherwise have to carry out an oil change at sea. However, the official party line at Mobil 1, as we expected, is that you should defer to your manufacturer’s recommendation on oil type, weight, and service ratings appropriate for your engine. Typically, if an engine maker does certify the use of a high-mileage oil, it is in combination with routine sampling of the oil to determine its condition.

Unfortunately, ye ol’ BMW diesel
D-50 has been out of production for many years now, so there would be no mention of Mobil 1 or sampling regimens in your manual, if you could track one down.

We did, however, have an informative discussion with Steve McGovern, vice president at Mack Boring and Parts Co., and Doug Rose of Volvo on the topic of oils. (Yanmar is currently involved in a joint project with BMW to produce marine engines in the 150- to 260-horsepower range that can use Mobil 1. Volvo sells a synthetic diesel engine oil.)

Both experts agreed that the owner of a typical sailboat auxiliary of less than 100 horsepower and logging 50 to 100 engine hours between seasonal oil changes probably wouldn’t get any added benefit from an extended-life oil since manufacturers’ specs call for changing the oil long before the "extended life" benefit of a synthetic kicked in.

"Synthetic oils get contaminated with acids, water, soot, etc., just like regular oils, and just because the oil is synthetic doesn’t mean that the oil change intervals go out the window," said Rose. "The use of a synthetic oil does not extend the oil change interval without oil sampling."

It is much easier, McGovern said, to justify the expense for synthetics in the trucking or shipping industry where the mileage numbers are huge, and where reducing the frequency of oil changes can mean a big cost savings.

A trans-Atlantic sailor planning to put many hours on the engine between oil changes might benefit from a high-mileage oil and oil sampling, but for most sailors, the existing mineral blends are fine, and a whole lot cheaper given the typical oil change requirements. It is also worth noting that it is probably not a good idea to put a low-viscosity synthetic oil designed for engines that run all the time into an engine that sits for very long periods or will be going into long-term storage.

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