Re: engine oil question

[PGAHOWELLS@domain.elided]

Hi
The ambient temperature in which you are operating is the big deal
10w-30   -20 to+20 Centigrade
10w-40  -20 to >+20 Centigrade
20w-50   0 to >+20 Centigrade
The ROM mentions API SE. Most of todays Engine oils are higher spec.  SE was 
followed by SF and then SG  and I believe there is even an SH now. These 
advances refers to the increasing ability of the oil to withstand reduction 
in the power of its additives, allowing it to last up to 12000 miles in 
modern engines. It is not recommended you keep it in that long in a Stag, 
because putting it crudely, it goes black in a Stag after 3000 miles which 
messes up its qualities. In a modern lowish mileage engine after 9000 miles 
it still looks fairly clean.
Are you in California. Then if it never goes below freezing use 20W 50. The 
numbers refer to the viscosity range. 20W is too viscous for quick starting 
in a sub zero winter temperature, hence for that we go down to 15W or 10W 
(brrrrr).
If you really want to know a lot more about this subject then you need to 
obtain input from a qualified lubricants engineer/chemist.
Peter H