Synthetic oils in older bikes
Following on from my earlier post about synthetics...
There is a commonly held belief that synthetic oils are not suitable for use in older bikes. This isn't generally true!
Do synthetic motor oils damage seals?
Any oil seals made after 1975 or thereabouts will be entirely compatible with any type of synthetic engine oil. (The same goes for synthetic gear oils and transmission oil seals.) It must be understood that everything associated with lubrication is thoroughly tested. The major oil manufacturers do not make oils that attack seals; seal manufacturers ensure that their products function correctly with modern lubricants.
Are synthetic oils too thin?
It is true that the best synthetic blends can be low viscosity (0w-20 for example), but they do not have to be! It is also true that the latest engines are designed to run on thin oil, which improves power output and fuel consumption. Even so, thicker synthetic based grades (10w-50, 15w-50, 20w-50etc) are available for air-cooled motors, older engines, or severe high temperature conditions. These grades can also benefit rebuilt classic engines dating back to the 1940s.
Do synthetics mean higher oil usage?
No. Oil consumption in well-maintained modern engines is mainly down to the oil evaporating at high temperatures. Synthetic base oils (specially the PAO and ester types) are very resistant to evaporation loss even in low viscosity blends, so oil consumption is minimised. But engines with worn valve guides, defective seals and worn piston rings will use oil regardless, so there is no point in using expensive synthetics in a worn engine.
Hope this helps to clarify the position!
oilman
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