Information about Engine Oil

Oil Facts

Service Intervals

Synthetic Oil

There are two main components that any motor oil is made of. There is a base fluid (sometimes called a base stock) and the additive package. The base fluid typically makes up the bulk of the oil. Additive chemicals are then added to enhance the positive qualities of the base stock and to overcome whatever negative qualities there may be.

Motor oil must create a film between moving parts to make them "slippery" which increases power, performance and efficiency. The film that a motor oil provides between metal surfaces does more than just lubricate though. By keeping engine components from coming in contact with each other, a motor oil also provides protection against wear.

Motor oil must also protect against corrosion of engine components. Oxidation of the oil and contamination from condensation and combustion by-products cause acids to develop in the engine oil. Additives in the oil are designed to combat these acids.

Motor oil is responsible for a large percentage of the cooling that takes place within the lower part of your engine. Your radiator (cooling system) is only responsible for cooling the upper portion of your engine. The rest (crankshaft, camshaft, timing chain, main and connecting rod bearings and many other critical engine components are cooled mainly by the motor oil. As oil passes through the system it is directed onto these hot surfaces in order to carry much of the heat away.

That is why running even a quart low on oil can cause higher temperature at the engine bearings and lower moving engine components. As this is not part of the liquid cooling system, your temperature gauge won't show this higher oil temperature until damage has already occurred.

The viscosity of oils are a key factor in oil performance. If the oil thins out too much, bearing surfaces can touch, resulting in metal-to-metal contact. Without the lubricant to act as a cushion, bearings and camshafts will gall. Cylinder walls also are subjected to high forces, and will suffer from piston and ring wear. If the oil is too thick it will take too long when the engine is cold to reach critical components and may not flow through some of the tight orifices fast enough when warm. Thick oil can also decrease fuel economy.

Viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperatures. The longer it takes, the higher the viscosity and the higher an SAE code. A single grade oil will have a much higher viscosity when cold and a lower viscosity at the engine's operating temperature.

A multi-grade motor oil can be created by adding special polymers called viscosity index improvers, or VIIs to the oil. A multi-grade oil will have the viscosity of the base grade when cold and the viscosity of the second grade when hot.

A typical 5w-30 petroleum oil is made of 5-weight base oil. At zero degrees Celsius (32 degrees F.) it behaves like 5-weight oil. Because of VI's, it will behave like a 30-weight oil at 100 degrees C. (212 degrees F.)

Some places in the piston have a normal operating temperature of at least 600 degrees, and turbochargers get even hotter than that. This causes thermal degradation. The problem occurs during high RPM. Oils can "shear back" to the lower number--just when it is needed to be thicker. A 5-30 can turn into a 5-weight oil.

Petroleum-based lubricants suffer from thermal degradation when exposed to high engine temperatures. When this happens, they also form varnish deposits, which can cause rings to stick to the pistons and plug up turbo oil passages. Once a petroleum based oil reaches over 475 degrees, it starts breaking down, turning into tar and varnish and then forms hard deposits that block the oil flow. Contaminates such as dirt, moisture and sludge will also lower an oil's capability to maintain viscosity.

To prevent sludge formation, a detergent-dispersant additive is used in engine oil. When sludge begins to accumulate in the engine, mainly by-products of combustion blowby, the detergent suspends the by-products, keeping them from interacting and in suspension until the oil is changed. If they combine, they'll form long chains of molecules that become sludge deposits. Detergent ingredients include chemicals that aid in trapping particles, dispersant additives that break down coagulating sludge, rust preventers and alkaline to neutralize the acidic nature of oil as it begins to oxidize.

However, heat and thermal cycling depletes the detergents, then the sludge will begin to coat the inside of the engine, plug oil passages and which can cause excessive wear and engine damage. This is an important consideration any time you extend oil drain intervals over recommended time or mileage.

As the engine operates, acidic by-products from the combustion process get past the piston rings and into the oil. The acids combine with moisture (every gallon of gasoline burnt produces 1/2 gallon of moisture) which can dissolve bearing surfaces.

Modern motor oils contain additives to combat the acid build up in the oil. As the oil becomes contaminated and turns acidic, the additives get used up. Preventing acid buildup is a very big reason for changing motor oil regularly. Short trip driving is the worst kind of driving for this problem as moisture is not boiled off during driving cycles.

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