Gasoline and diesel engine oil quality levels established jointly by API, SAE, and ASTM, and sometimes called SAE or API/SAE categories; formerly called API Engine Service Classifications.

Related Terms


A valve used to mix gasoline with engine oil to permit easier starting of the gasoline engine in cold weather.


In an auxiliary diesel engine bypass type lubricating oil system, the main lube oil pump forces some of the oil used by the engine through a filter.


  1. Explosions of mixtures of air and lubricating oil in the compression chambers or in other parts of the air system of a compressor. 2. Continuation of running by a gasoline spark-ignition engine after the ignition is turned off. Also known as run-on.


Rated performance for a burning oil as determined by specified ASTM (American Society for Testing and Materials) tests.


Apparent viscosity in cP determined by Brookfield viscometer, which measures the torque required to rotate a spindle at constant speed in oil of a given temperature. Basis for ASTM Method D 2983; used for measuring low temperature viscosity of lubricants.


  1. A process in which oil is passed through a filter as it comes from equipment and then returned for reuse, in the same manner that crank case oil is cleaned by an engine filter. 2. A method in which solids are removed from oil by treatment in settling tanks.


The diesel engine is a type of internal combustion engine which ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber.
The marine diesel engine is a type of diesel engine used on ship. The principle of its operation is as follow: A charge of fresh air is drawn or pumped into the engine cylinder and then compressed by the moving piston to very high pressure.
When the air is compressed, its temperature rises so that it ignites the fine spray of fuel injected into the cylinder. The burning of the fuel adds more beat to the air charge, causing it to expand and force the engine piston to do work on the crankshaft which in turn drive the ship’s propeller.
The operation between two injections is called a cycle, which consists of a fixed sequence of events. This cycle may be achieved either in four strokes or two. In a four-stroke diesel engine, the cycle requires four separate strokes of the piston, i.e. suction, compression, expansion and exhaust. If we combine the suction and exhaust operations with the compression and expansion stroke, the four-stroke engine will be turned into a two-stroke one.
The two-stroke cycle begins with the piston coming up from the bottom of its stroke, i.e. bottom dead center (BDT), with the air inlet ports or scavenge ports in the sides of the cylinder being opened. The exhaust ports are uncovered also. Pressurized fresh air charges into the cylinder, blowing out any residual exhaust gases from the last stroke through the exhaust ports. As the piston moves about one-fifth of the way up, it closes the inlet ports and the exhaust ports. The air is then compressed as the piston moves up.
When the piston reaches the top of its stroke, i.e. the top dead center (TDC), both the pressure and the temperature of the air rise to very high values. The fuel injector injects a fine spray of fuel oil into the hot air and combustion takes place, producing much higher pressure in the gases.
The piston is forced downward as the high-pressure gases expand until it uncovers the exhaust ports. The burnt gases begin to exhaust and the piston continues down until it opens the inlet ports. Then another cycle begins.
In the two-stroke engine, each revolution of the crankshaft makes one power or working stroke, while in the four-stroke cycle engine, it takes two revolutions to make one power stroke, that is why a two-stroke cycle engine will theoretically develop twice the power of a four-stroke engine of the same size. Inefficient scavenging and other losses, however, reduce the power advantage to about 1.8.
Each type of engine has its application on board ship. The low speed (i.e. 90 to 120 r/min) main propulsion diesel operates on the two-stroke cycle. At this low speed the engine requires no reducing gearbox between it and propeller. The four-stroke engine (usually rotating at medium speed, between 250 to 750 r/min) is used for alternators and sometimes for main propulsion with a gearbox to provide a propeller speed of between 90 to 120 r/min.


An engine test in a six-cylinder spark-ignition Chevrolet engine to evaluate crankcase oil oxidation stability, bearing corrosion, and engine deposits.


A term used to describe a diesel engine in which air flows into the engine by means of only.


The ash content of fresh, compounded lubricating oil as determined by ASTM Method D 874. Indicates level of metallic additives in the oil.

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