some interesting reading from the castrol website
THE ROLE OF OIL IN A CLASSIC CAR
The formulations required for modern vehicles are very different from those needed for older vehicles. Oils for modern engines comply with the latest API ratings of SG and SH and are ideal for the design of a modern engine. A classic car engine has the opposite characteristics with cork/graphite/rope seals, low pressure cog driven oil pumps, wider oil ways with greater dependence on "splash" and "cling" lubrication, lower revving with lesser machine tolerances. Such a widely different specification demands a totally different lubricant.
Inadequate detergent will result in gum and lacquer clinging to the hotter engine components - too much detergent can cause a build up of metallic ash in the combustion chambers of older engines. In older engines with traditionally high oil consumption, this will cause detonation and pinking.
In older engines where the carbon has built up over a number of years the detergents can also have a scouring effect causing the carbon to flake off, blocking up oil galleries and spray jets. High levels of detergent will "wash" traces of carbon from seals and gaskets, revealing oil leaks.
Inadequate anti-oxidant and the oil will permanently thicken during high temperature motoring, with large amounts of gum and varnish clogging filters and piston rings.
Inadequate anti-wear additive and the oil film between moving parts breaks down prematurely, resulting in metal to metal contact and irreparable damage.
Inadequate corrosion inhibitors and engine internals become pitted with corrosion and rust from acids and water formed during combustion.
Inadequate dispersing results in soot, wear metals and the by-products of combustion settling out in the sump to form a thick sludge, that will block filters and oil ways. Inadequate pour point depressant and the oil ceases to flow at low temperatures, with excessive strain on the oil pump or in certain cases, oil starvation on start-up causing complete failure of the lubrication system.
Last edited by sudboy1490; 30-07-10 at 17:42.