Chapter 3

Oil

It is important to follow the manufacturer's specifications when choosing the oil to put in your vehicle's engine. Oil is the life blood of your vehicle's engine and using the wrong oil can void your warranty and cause the engine to malfunction.

There are three different things to take into account when choosing oil.

1. There are detergent and non-detergent motor oils. This is an easy decision because all new vehicles today are best operated with detergent motor oil. If you are dealing with an older vehicle more than 25 years old you should check with the manufacturer to see if detergent motor oil is recommended.

2. When choosing engine oil it is important to get the correct viscosity grade. Viscosity refers to the resistance to flow of a fluid. A fluid with a low viscosity flows easily and is commonly called thin and a fluid with high viscosity is often described as thick.

The correct viscosity grade should be clearly indicated in your vehicle's owner's manual. Note that the manufacturer may suggest different viscosity grades depending on driving temperatures and conditions. Most manufactures will recommend a multi-viscosity grade oil such as 5W-30, 10W-30, 10W-40, 20W-50, etc. However, keep in mind that straight weight oils do exist, so again please check your owner's manual.

Multi-viscosity grade oils are made to meet an engine's needs over a wider temperature range than single weight oils. As a general rule the lower the numbers the lighter the oil. Generally, at higher operating temperatures the heavier the oil that should be used and vice versa in colder temperatures. As such, one would use heavier oil in the summer and lighter oil in the winter. For example, SAE 20W-50 acts like a 50 weight once your engine reaches normal operating temperatures and like a 20 weight oil at colder temperatures and at start-up.

3. The third thing to determine is the proper American Petroleum Institute (API) service category. Engine categories are classified by a two-letter code. Diesel oil categories start with the letter C while gasoline engine oils start with the letter S. It is common to associate the C with a "compression ignition" system found in diesel engines and to associate the S with a "spark ignition" system found in gasoline engines. The second letter is simply a sequential designation assigned over time to improving qualities of engine oil. The API designation system was implemented in 1971 with the introduction of the SA classification. Most oil manufacturers only market the most current API service categories, which today include service categories SJ, SL, and SM for gasoline engines and CF, CF-2, CF-4, CG-4, CH-4, and CI-4 for diesel engines.

Your vehicle's API service category should be clearly indicated in your vehicle's owner's manual. Note that vehicles equipped with a turbo charger generally specify a turbo rated oil and often you will find oil bottles labeled specifically for turbo charged vehicles. However, the surest way to be certain you are using the correct oil is to follow your owner's manual's recommendation as to the correct API service category.

If you have an older vehicle which was manufactured prior to the release of the currently available API service categories then your vehicle's owner's manual will obviously call for the service categories available at the time the vehicle was manufactured and the owner's manual was printed. However, the oil manufacturers keep improving engine oil so generally it should not be a problem to use the latest API service category oil.

Engine oil should be changed regularly in accordance with your vehicle's owner's manual, but as a general rule, once every 3,000 miles. Engine oil is doing a lot more than simply lubricating your engine's moving parts. Engine oil is designed to carry combustion by-products away, as well as deal with small amounts of accumulated water, as well as dirt and dust that enter through the engine's air intake system.

Furthermore, acids can form in your engine as a result of a reaction between the water and other contaminants. If you develop a fuel or coolant leak (which should be fixed immediately to avoid further damage) the engine oil needs to deal with these problems as well. Over time, all of these contaminants grow in your engine and while the oil filter can remove certain particles in the oil, it is the oil's additives that deal with these other things.

Furthermore, at some point these additives lose their effectiveness and the oil stops doing its job. Then it is important to change the oil at this time. There is no absolute rule of thumb as to when an oil will become ineffective nor can you determine this by just looking at the oil. This is why manufacturers give you a maintenance schedule, which you should follow.

However, there are certain things that will effect engine life such as a damaged Positive Crankcase Ventilation (PCV) system, driving in dusty or sandy conditions, short trips of 10-15 miles or less, long-term idling, pulling trailers, etc. These types of things can cause your oil to wear out sooner. When in doubt, our suggestion is to change your oil sooner rather than later. After all, an oil change is far less expensive than overhauling your engine.

If your vehicle emits smoke at start-up there are generally three possible causes. See Chapter 11 for the possible causes.