07-02-2019, 12:29 AM
(This post was last modified: 07-02-2019, 12:36 AM by Bob Culver.)
Until the 30s Seven engine oils had no anti wear additives etc (API SA) and relied soley on viscosity. Considerations of consumption, noise and leakage were other factors favoring relatively thick oils.
Thick oils sap power. According to charts in the book Which Oil the crossover point between 20w/50, 15w/40 and 30 is way below 0 deg C. So, relatively, on 20w/50 engine is forever labouring to some degree. A thinner mulitigrarde would seem useful.
There is some question about the behaviour of older style (now the cheaper) multigrades under load but hundreds of millions of vehicles with loadings far greater than Sevens ran/run on these for decades and acheived wear rates vastly less than previous generations on low additive monogrades (API SB). The effective API rating of Classic oils is a bit of a mystery and probably include features of later ratings, but it seems folly to pay a premium for a 1940s era oil.
Most Sevens devour oil and change periods are brief anyway. Expensive premium or special oils seem wasteful.
Thin oils for winter ensure immediate circulation, important on an ohc pressure fed car started at -20C and immediately run up to motorway revs. But with Sevens there is oil everywhere whatever.
Thick oils sap power. According to charts in the book Which Oil the crossover point between 20w/50, 15w/40 and 30 is way below 0 deg C. So, relatively, on 20w/50 engine is forever labouring to some degree. A thinner mulitigrarde would seem useful.
There is some question about the behaviour of older style (now the cheaper) multigrades under load but hundreds of millions of vehicles with loadings far greater than Sevens ran/run on these for decades and acheived wear rates vastly less than previous generations on low additive monogrades (API SB). The effective API rating of Classic oils is a bit of a mystery and probably include features of later ratings, but it seems folly to pay a premium for a 1940s era oil.
Most Sevens devour oil and change periods are brief anyway. Expensive premium or special oils seem wasteful.
Thin oils for winter ensure immediate circulation, important on an ohc pressure fed car started at -20C and immediately run up to motorway revs. But with Sevens there is oil everywhere whatever.