Your Engine's Life Blood...............Ed Sherman

You go to the doctor for a physical exam and one of the first things they want is a blood test. Why? Easy, from what's found chemically in your blood your doc can tell a lot about what's going on with the rest of you. Important stuff. Well your engine's oil is its life blood and it is just as important as the red stuff running around in your body. Just like the blood in your vains, engine oil does a lot more than just lubricate your engine. It also helps to keep things cool and capture contaminates that build up inside your engine. It fights corrosion of vital metal parts that make up your engine's innards, and neutralizes the harmful by-products of engine combustion..

 The thing is, most people really don't understand some of the nuances of their engine's oil, and how to make the correct choice to ensure the best service and long life for their engine. One obvious question is: Do you have to use the OEM brand of oil sold by my engine dealer? No! But, you'd better be certain you're not substituting with an oil of inferior rating and specification, especially if your engine is still covered by warranty. So let's start out by looking at a typical factory recomendation for the oil to be used in a four-stroke outboard engine, in this case I've randomly selected a 50 HP Yamaha. Here's the recommendation from the engine service manual (the same info will be found in your engine's owner's manual).

Engine oil: 4-stroke motor oil

Engine oil grade: API -SE, SF, SG, SH or SJ

                       SAE- 10W-30 or 10W-40

In this case, no particular brand is mentioned, just the cryptic codes under API and SAE headings. This is important, because the oil grade used is the key here.

Oil Grades Demystified

All engine oils distributed throughout North America are rated based on Standards established by the American Petroleum Institute (API). The letter "S" designates a specific "service" category, we'll look at those more closely in a minute. All gasoline fueled engines, inboard, outboard, it doesn't matter as long as its not a two-stroke outboard engine, will require oil of a certain, or sometimes multiple service categories. By comparison, all diesel engine oil will have a letter "C" designation, which stands for commercial. The second letter of the API grade designation follows a historical sequence that looks like this:

SM- Introduced in 2004, its the highest rating avaliable as of November 2009. Some SM rated oils may also be qualified for an energy conserving designation.

SL- Rated for 2004 and older engines. Still a current designation

SJ- Rated for 2001 and older engines. Still current.

SH- Obsolete, for 1996 and older engines. Still valid if preceded by current "C" categories.

SG- Obsolete, for for 1993 and older engines.

SF- Obsolete. Not suitable for engines manufactured after 1979........

and so on all the way back to "SA", which is considered not suitable for engines built after 1930.

For diesels, the sequence looks like this:

CI-4- Is currently the highest grade. Introduced in 2002. Designed to be effective with low-sulfur diesel fuels.

CH-4- Introduced in 1998. Again, designed for low sulfur content diesel fueled engines.

CG-4- Introduced in 1995 for high-speed and severe duty service. Low sulfur fuels and 4 stroke diesel service.

CF-2- Still current, introduced in 1994 for use in severe duty two-stroke diesel applications. (Older Detroit diesels). ......and so on all the way back to CA designations.

So, when you pick up a can of oil for your engine, you need to study the label carefully and look for the circular specification "donut" as some people refer to it. An example is shown here:

In the photo you can see just under the Texaco star the API designators as well as the SAE ratings, which we'll talk about next. Notice that this particular oil has multiple ratings, as most oils do today. You should be concerned that the S or D ratings at least meet the ratings required by your engine manufacturer. There is no problem using an oil with a higher rating than specified by your engine maker, just don't use one with a lesser rating. Remember that the deeper into the alphabet the second letter in the designation goes, the higher the rating.

SAE and Viscosity

Besides the quality of the oil, you need to be concerned about the viscosity, or thickness of your engine's blood. So to begin, who's SAE? Society of Automotive Engineers, another standards writing group. SAE has established Standards for engine oil viscosity indexes. In general, small numbers mean thinner oil or a lower viscosity. Bigger numbers mean thicker oil. Some oils are what we call "multi-viscosity" designated by 10W-30 or 10W-40 as examples. Here, the "W" simply stands for winter and the two numbers describe the oils ability to flow at certain temperatures, both high and low. Some engines will specify different oil viscosities for engine operation at higher or lower ambient temperatures, i.e. winter vs. summer. Simply put, you need to be sure that the oil you select matches the viscosity index specified in your engine owner's manual.

Is mixing brands of oil OK?

The truth is its OK and won't really hurt anything as long as the viscosity and API designators are in line. But, many service technicians and dealers will strongly recommend against this practice. The practice should be avoided for sure. Modern engine oils are extremely complex molecularly cross-linked blends of not only oil, but complex chemical additives designed to enhance the properties of the oil. Every oil vendor has their own take on this process, so that means the actual chemical formulas will vary somewhat. It is a good idea to pick your favorite and stick with it, not mixing brands unless it can't be avoided. This is your way of ensuring that you'll get the most out of every oil change and all the benefits of the additive package engineered into whatever brand you choose.

Special Designators

Finally, within the circle label or donut, the oil you select may have one of several additional designators, Energy Conserving, or in the case of diesels, you may see CI-4 Plus. These designators are special and in the case of "Energy Conserving" simply means that use of this oil may result in fuel savings. This designation is typically intended for oil used in cars, vans and light trucks, but it can't hurt in your boat either. Regarding the CI-4 "Plus" designation, it identifies oils designed to provide a higher level of protection against soot-related thickening of the oil, or conversely, thinning of the oil caused by a phenomenon known as "shear" that occurs in diesel engines. So, in closing this entry, before you do this:

Read the Label!!!!!!!!!!