DIFFERENT TYPES OF MARINE ENGINE OILS Not all marine engine oils are created equally and they can be divided into three basic groups, specifically mineral, synthetic blend and full synthetic. Non-synthet- ic oil, often referred to as mineral-based oil, is a product of the petroleum refining process, where the different elements of crude oil are separated through a distilla- tion process. This is the same process that produces gasoline, diesel fuel and other petroleum products. Lubricating oils manufactured through this process are con- sidered Group I (gear oil, industrial) and Group II (engine oil) and work well for many applications, but their molecular structure is inconsistent. Visualize the molecules of non-synthetic lubricants like a jar full of different sized rocks.
Synthetic lubricants (Group III) are produced through a (chemical synthesis process) higher grade refining process where molecules are broken down and rebuilt into a uniform structure. The higher the refining process, the more pure the base oil becomes and typically, the higher the lubrication quality of the oil. The advantage of synthetic lubricants is they have a consistent molecular structure. If the molecules of a non-synthetic lubricant are like a jar of rocks, picture the molecules of a synthetic lubricant like a jar of uniformly-sized marbles. Now imagine sticking your hand in each jar…it would definitely be easier to slip your hand into the jar of marbles!
Semi-synthetic lubricants are blend of synthetic and mineral base oils and typically contain up to 30-percent synthetic. Semi-synthetic oil imparts some level of synthetic lubrication qualities and oil stability to a mineral blend. While not as high a quality of lubricant as full-synthetic, it is a higher quality lubricant than a standard mineral oil. DECODING MARINE OIL…READ THE LABEL Let’s break down a typical marine engine oil label and determine its intended usage. For this analysis, we’ll use 25W-40 as our example. So what does this mean? The“W”in the label stands for winter and the other parts of the nomenclature show that this is a multi-viscosity oil that thins out to 25-weight in colder temps (winter) to provide less friction for faster engine starts. During warmer months it thickens up its viscosity to 40-weight for maximum lubrication potential. Boaters living further north up the coast typically prefer a 10W-30 oil.
As a final tip on marine engine oil, fall is the best time to do a 100-hour/annual oil and filter change when winterizing your motor. You want to remove all the acids that can cause corrosion and other damage to your engine. Doing the oil change in fall also removes any water intrusion before it can separate from the oil, freeze and cause corrosion. In next month’s column, we’ll review the“factory-approved way”to check your engine’s oil level and how to interpret the dipstick.
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