Difference between 20/50 and 30w

[morrisminor]

I've been using 20/50 in my Ruby since the engine was rebuilt,  would using straight 30 be better for it in the winter ? What's the difference ?

[Chris KC]

No.
20W50 will be slightly thinner at low temperature than SAE 30 - which is a good thing, as all oils are way too thick when cold, which is where most of the wear and damage occurs.
It may be slightly thicker at running temperature than SAE 30, which is arguably not a bad thing on an 'old' engine, especially if it is driven hard.
The major advantage of multigrades is better flow under cold starting conditions than straight oils. That's what they were developed for.

[Jays]

I am pleased to see this comment. New to Sevens and I was about to post for advice regarding recommended oil for the engine and gearbox!

[Bill Sheehan]

I am pleased to see this comment.  New to Sevens and I was about to post for advice regarding recommended oil for the engine and gearbox!

Jays - welcome to Austin Sevens.  But a favour - PLEASE read the volumes (challenging War & Peace) on this subject before you unconsciously start off another series of boring opinions.  Just hit "Oi"l on Search button above.  Appreciate your help.   Cheers,  Bill in Oz

[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.