Richard L. Parish | 11/18/2004 8:54:26 PM
Oil is the lifeblood of any engine. With the wrong oil, not enough oil, or dirty oil, your engine can be rapidly damaged. Without oil, your engine will freeze up within seconds. Neglecting your oil can be a costly mistake.
What Does Oil Do?
The primary purpose of engine oil is to form a lubricating layer between the metal surfaces in your engine to reduce friction and engine wear. The oil also helps dissipate the heat generated by the engine. Furthermore, oil flushes out dirt and combustion byproducts and holds them in suspension until drained and replaced.
Viscosity is an indication of how flowable a liquid is. Honey has higher viscosity than water. The higher the viscosity grade of an oil, the thicker and less flowable it will be. Viscosity is rated according to a standard developed by the Society of Automotive Engineers (SAE).
Single-grade oils are rated SAE 10, SAE 20, SAE 30, etc. Multigrade oils will have a rating number like SAE 10W-30. Multigrade oils are light oils that have a polymer added to increase the viscosity at operating temperatures. An SAE 10W-30 will be as thin as an SAE 10 oil when cold (at startup), but, as the engine warms, the polymer will cause the oil to thicken so that it acts like an SAE 30 oil. Thus, the oil will have reduced friction at startup but provide adequate protection while operating.
The correct oil for your engine will depend on the ambient temperature in which you will be operating (thinner oils at lower temperatures). Many lawn and garden engine manufacturers recommend using 30W or 10W-30 oil in the temperature range generally found in Louisiana, but you should consult your own operator’s manual for recommendations specific to your engine.
The other critical rating for oil is the American Petroleum Institute (API) rating (Figure 1). This rating on a container of oil is your guarantee that the oil meets minimum API standards for engine oil. As automotive engines have become more complex and sophisticated, engine oil has evolved to higher quality levels.
Before 1968, API SC oils were recommended for automobile engines; now, oil for automotive engines has evolved through SD, SE, etc. to the current API SJ rating. Oil rated API SJ will be adequate for any small gasoline engine. Most oils now sold will bear the API SJ seal, but check the container to be sure.
Diesel engines are rated with a different scale. The API rating for current diesel engines is CH-4. Diesel engines do require different oil, so be sure to use an API C-rated oil in diesel engines. Just remember, S = spark ignition, C = compression ignition. A few brands of oil meet both gasoline and diesel criteria.
So-called synthetic oils are available at considerably higher prices than normal oil. In some cases, longer oil change intervals are claimed because the polymers in the synthetic oils do not break down as rapidly; however, the oil still gets dirty just as fast in lawn and garden use, so it needs to be changed just as often. This makes synthetic oil much more expensive to use.
Many brands of oil are available and prices vary widely. The more expensive brands may contain some additives that the less expensive brands do not contain, but the appropriate API rating and viscosity grade are all you really need, especially in a lawn and garden engine. The cheapest discount brand that meets the API rating and viscosity grade recommended by the engine manufacturer is quite adequate. There is no need to buy expensive oil.
The shelves of your auto parts stores and discount stores contain many oil additives. You don’t need them if you use the correct viscosity and API grade of oil.
Any oil needs to be changed regularly. Oils break down with exposure to heat and friction. The long-chain molecules break up and the oil thins. Also, the oil gradually picks up a load of dirt and combustion byproducts. This old oil must be drained and replaced when needed. It is not adequate to keep adding new oil to the crankcase; the old, dirty, broken-down oil must be drained and replaced.
Choosing the correct oil is important to the life of your engine. Even more important is keeping the oil at the right level and changing it as needed. You can economize by using lower priced oil - if it meets the required API rating and viscosity - but don’t cut back on oil change intervals.