Lubricate engine parts
Inside your engine, pistons, crankshafts, camshafts, and other parts are rotating at incredibly high speeds – sometimes at several hundred or several thousand revolutions per minute. Engine oil lubricates these metal parts to keep wear and burnout to a minimum.

Create tight seals
Pistons do not fit tightly into the cylinders in your engine. Instead, they are surrounded by a tiny gap that allows them to move freely. If this space is not sealed tightly, the energy produced from combustion can escape from this gap, resulting in power loss and blow-by gas emissions. In older engines, this gap often gets wider due to repeated wear from the piston rotations inside the cylinder. If this happens, a tight seal can be recreated by overhauling the engine and frequently replacing engine oil with new, high-viscosity lubricant.

Cool hot engine parts
The combustion and friction inside your engine creates extremely high temperatures. Engine oil also works as a coolant that absorbs heat as it circulates among the engine parts, then returns to the oil pan to cool. Engines designed for high-speed driving (such as in sports cars and race cars) generate even higher temperatures, and are often equipped with a separate oil cooler.

Clean the engine
Engines produce a variety of contaminants as a result of combustion and rotational motion, which are often called sludge. Sludge build-up will not only affect engine performance, but will also shorten engine life. Engine oil plays an important part in absorbing and/or dispersing these contaminants to prevent accumulation. Black engine oil is usually a sign that the oil is doing its job and cleaning the engine, but there is a limit to how much sludge oil can absorb. That is why oil must be changed on a regular basis.

Prevent rust
Combustion produces scorching temperatures inside your engine, which are much higher than the surrounding air. This creates a temperature gap that often causes condensation, which in turn encourages rust formation. Rust can both deteriorate engine performance and shorten engine life. Engine oil helps prevent rust and extend the life of your engine.

Oil grades and viscosity

Standard engine oil (mineral oil)
Mineral oil is made by refining crude oil, and is still the most widely used type of oil today despite some disadvantages (oil performance depends on crude oil quality, and mineral oil’s inconsistent molecular weight makes it break down quite easily). However, the performance of mineral oil has been improved significantly for normal driving use, and high-end mineral oils with superior fuel efficiency are becoming more popular. There is still room for improvement in terms of the overall functionality of mineral oil, but when it comes to cost performance, engine oil made from fuel-efficient mineral oil is fairly competitive.

Semi-synthetic oil (blended with chemically synthesized oil)
Auto Bank uses semi-synthetic oil in all of its standard oil changes. Engine oil that blends chemically synthesized oils with mineral oil delivers better performance at a lower cost. Semi-synthetic oil works almost as well as pure synthetic oils in most conditions aside from ultra-high performance racing applications. Customers can expect a good balance with semi-synthetics, which are relatively affordable without compromising functionality.

Synthetic oils (chemically synthesized oil)
Synthetic oil is the highest-ranked engine oil and delivers superior performance. It is made from synthetic oils with a scientifically modified molecular sequence, resulting in durable oil film at high temperatures, excellent lubrication at low temperature, and advanced cleaning performance. Some luxury car manufacturers require the use of synthetic oils in their vehicles. Synthetics are recommended for turbo-chargers and sports cars, and for people who need to take special care of their engines. However, because synthetic oils are rather costly, they may not be the best choice for standard oil changes in normal cars under normal driving conditions.

Understanding viscosity
Engine oil viscosity is indicated together with a standard API symbol. However, the indication is typically large, even separately indicated with the symbol. A typical indication is shown below.　　　　　　　　　

SAE 10W-30

The letters SAE give you the viscosity classification, and sometimes indicate API performance. 10W indicates a low-temperature viscosity index of 10, and the capital “W” stands for “winter”, emphasizing that 10 indicates cold-weather performance.
The 30 after the hyphen indicates a viscosity index of 30 at high temperatures. Engine oil with these types of indications are called multi-grade oils.
Single-grade oils, on the other hand, only provide a high-temperature viscosity rating (e.g. SAE 20). These oils are designed for compressor engines, and are not typically used in motor vehicles.

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