What is the issue?The life of your engine depends in no small part on the quality of the oil you put in it as that is its lifeblood. There is a tendency to play it safe and buy the manufacturer's branded engine oil when it comes to service. This can be disproportionately expensive and add substantially to the annual running cost of a vessel.
Why address this?This expenditure may be dramatically reduced with some forethought and planning.
How to address this?Engine manufacturer-branded and premium branded oils often trade on your uncertainty and the wish to care for your engines - wanting to give them the best. Of course, they may have some excellent additional properties and this is not disputed, but as long as you buy a diesel rated oil from a trusted manufacturer that matches the engine manual's specification you will be fine.
In a normal everyday unstressed diesel yacht engine, but not a highly tuned high-end performance vehicle engine for instance, any decent brand named oil would be more than adequate. That's not to say lubricating oil does not work hard in a diesel engine, in fact, it works much harder than the oils of a petrol engine owing to the higher temperatures, greater compression loads, and never more so than in lightweight high-speed turbocharged types of diesel engine found in modern production boats.
Boat engines typically have a steady running life but they do tend to be run too cool. This happens when the engine is only used to pull away from the harbour, so that the sails may be set, and/or when the engine is run for long hours with a light load to charge batteries. In these cases both lead to moisture condensing in the engine which combined with sulphur in the fuel creates a sulfuric acid that degrades sensitive engine surfaces. They also generate far more carbon than normal that can coat up piston rings and valves leading to a loss of compression and other problems. So diesel engines can be dirty and especially so on cruising boats where the engine oil has to work particularly hard to deal with the carbon and sulphur.
It is therefore essential to get the correct specification of oil because diesel engine oils are specially formulated to keep harmful by-products of the combustion process in suspension. The widely used American Petroleum Institute (API) uses the letter C, for Commercial, to designate oils rated for use in diesel engines. This is then followed by another letter to indicate the additive components in the oil, with the better packages having letters that appear later in the alphabet.
All specifications prior to CH4 are now largely obsolete and are suitable for older engines more than 10 years old. They do not provide the same level of performance or protection as the more up to date CH4 & CI4 specifications. If you want a better more up to date oil specification then look for SL, SM, CH4, CI4 - list available as a downloadable PDF . However, if you are in anyway departing from the specification of the engine manual, take advice from an engine dealer or even better the manufacturer. However the lower cost, less premium brand of diesel engine oils that are rated to meet the specifications of the engine, offer exactly what your engine requires and meet the warranty requirements.
A good suggestion is to go to a diesel workshop and take advice on what they feel is a good quality oil. When there, if they have a quantity that meets your specification, ask if you can buy a large quantity oil drum of it from them, or if not their supplier, and stock up for several years sailing. Better still, if you buy in large quantities pumped into your own cans from commercial fifty-gallon drums you can achieve enormous savings.
The same can be said for oil filter or fuel filters. Ask the machine shops which they can recommend, as slightly different brands of the same quality that fit your system offer vastly different prices.
To a certain extent, the frequency of oil changes is much more important than the choice of oil. Change oil at the end of season, if you have an end of season. If you don't run your engine all that much, or run it lightly loaded, then just change the oil a little more often. Always run the engine after changing the oil to leave clean oil on all surfaces. Also, run and warm up the engine prior to draining the oil and always change the filter at the same time. A certain amount of mechanical sympathy and attention will ensure a better service life than a high priced oil label.
With thanks to:Michael Harpur, Yacht Obsession.
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