Mineral oil starts life in an oil well. It’s the same stuff that we’ve been using for years but is better engineering these days. Semi synthetic as the name implies its blend of mineral and synthetic oil. Synthetic: mineral oil that’s been chemically processed. Better low temperature, with higher film strength. In modern engines, reduces emission and fuel consumption. A measure of the oil’s viscosity (thickness resistance to flow) at low and high temperatures. Lower numbers mean lower viscosity. You’ll find this in the hand book of more modern Land Rovers for example; a Td5 should run ACEA A1 and B1, or B2 oils. They’re also quoted on oil containers or oil manufactures web site.
Multigrade, polymers expend when heated, so oil that’s thin when cold (requiring less effort to turn the engine in cold weather) become thick when the engine is warmed up. Molecules expend like a spring so they take up more room, even though the oil is thinned by high operating temperature a multigrade shows two SEA numbers for example 20w50
Monograde, all oils were monograde originally multigrade were in general use by the 1960s. For a while, old style monogrades were still essential for older Land Rovers, because modern oils contained additives harmful to older material seals and some bearing materials Additives are now improved and classic multigrade oils that better suit older vehicles are available. Monograde are still available, though, if you want to follow the old Rover manuals to the letter.
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