Originally Posted by joo5t
Older engines with their larger operating clearances demand the higher viscosity oils to achieve an adequate oil film thickness. Using a modern low viscosity oil in engines could be a recipe for disaster with a danger that the oil film will break down in the bearings, allowing metal to metal contact to take place with the inevitable consequences !
Very good point, and quite true however dont be fooled by modern oils being thin, they are not, they come in all the traditional viscosities and thinner ones as well.
Cheers
Simon.