Motor oil is a lubricant used in internal combustion engines. The lubricating oil creates a film separating the surfaces of adjacent moving surfaces, minimising contact between them, decreasing heat caused by friction, reducing engine component wear thus protecting the engine.
In petrol engines, the top piston ring can expose the engine oil to temperatures of 160ºC. In diesel engines, the top piston ring can expose the engine oil to temperatures over 315ºC. Engine oils with high viscosity indexes thin less at higher temperatures.
Vauxhall in association with General Motors supply the following oils;
Clicking through to each engine oil type gives further information about API (minimum performance standards for lubricants), ACEA (performance/quality classifications tests in Europe which are arguably more stringent that API and ILSAC standards, Kinematic Viscosity, Viscosity Index, Flash Point, Pour Point and Total Base Number.