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Oil Facts



Mineral Oil - This is the 'black gold' that comes out oft he ground and is refined from crude oil.

Semi-Synthetic Oil - A blend of mineral and synthetic base stocks. Intended to have the quality and benefits of full synthetic without the cost.

Sythentic Oil - Despite the name, the majority of synthetic oil is derived from mineral oil and also consists of Polyalphaolins (PAO), which come from gas extraction of crude oil. Main PAO is polyolester (NOT polyester!) and syntheics will mix happily with conventional mineral oils, meaning that you can add one to another without fear of undue engine problems.



  • SAE 5W, 10W, 15W and 20W ratings are oil thickness (viscosity) measurements at –25°C, -15°C and –10°C respectively. This is all to do with cold starts in winter conditions. 5W and 10W are really intended for severe North European (or American) winters.
  • SAE 20, 30, 40 and 50 (60 is an obsolete spec originally for large air-cooled aero engines) all measured at 100°C, a typical sump temperature in a hardworking engine. SAE 50 gives the best protection in hot climates where oil temperatures may exceed 100°C.
  • Once an engine has reached its working temperature (if over 70°C) the SAE "W" rating has no effect on the engine.
  • Wide-range multi grades (5W/50 etc.) were originally intended for severe climates where cold starts down to -20°C could be expected, followed by prolonged high-speed motorway use. The normal lubricants for moderate climates are 10W/40 (Northern Europe) and 20W or 15W/50 (Southern Europe). Apart from cost, wide range multi grades have a very high polymer content and can suffer from "shear down" effects (loss of oil viscosity during use). It is interesting to note that "MOBIL I RACE", specially aimed at the motorcycle market, is a 15W/50 so as to handle small high-revving motors where the MOBIL I is 5W/50 [now 0W/40, 1998].
  • A "synthetic" oil does not automatically guarantee extra engine protection. Those based on synthetic hydrocarbons (PAOs) last longer, but give no better wear protection than a mineral-based oil. Those containing the more expensive synthetic esters also contribute to anti-wear performance; A 10W/50 "pro-4 race", based on a 100% ester/PAO mixture, is near the end of its development programme, but it will be expensive. It is mainly intended for "super-bikes".