The Haynes manual says API grade SE or SF 10/40. I am ok with 10/40 but not sure what API grade SE or SF means, so any clarification is appreciated. Should I be using a semi synthetic oil? as oils have improved since my wing was made in 1985. I am in the UK and temperatures range typically -5c in winter to +30 in summer, average is 10c to 25c.
Daveski

... Howdy ... I use a 10/40 syn. Blend in my 85 ltd. ... Happy trails ...

i head to autozone for some castrol t4 10w 40