Up until the very early 1960s, fairly basic oils, generally SAE30 oils, were used in car engines. Towards the end of the 1950s a major development took place in Britain which forced oil companies to rethink vehicle oil. Britain was at the forefront of this development and ahead of the USA at the time. The major late 1950s development was, of course, the introduction of the Mini and the problems presented by having the engine and gearbox sharing the same oil, something only seen previously in motorbikes.
Initially, oils such as Castrolite 10w-30 were recommended for the Mini but the use of these thin oils often led to piston scuffing and gearbox problems. The solution was the introduction of a heavier 20w-50 multigrade oil. Many years later the recommendation was changed to 10w-40, to help with fuel economy, but the result was a host of gearbox warranty claims.
Because oil is shared by the engine and gearbox in a Mini, frequent oil changes are even booklet states that: “In some circumstances it would be wise to change the oil after only 3,000 miles or three months.” Today it is best to change both oil and filter in all Minis every 3,000 miles or six months (whichever is first), or perhaps 6,000 miles or six months in a car which covers 12,000 miles or more a year. If the Mini is not in use, or has covered minimal mileage, a two-yearly change will suffice. Most engine wear happens in the first 10 minutes of running from a cold start. If a Mini covers 3,000 miles a year, and it is all two-mile runs from cold, the oil should be changed at six months or 1,500 miles.
