Originally Posted by Capt.Bill11
Straight 30w, 40w or 15-40w.
Truth is you could pretty much put most any weight oil in a Lehman and it'll run on it for ever.
I've noticed that the stores that sell large quantities, like 1 and 2.5 gal, in the south it's all straight weight and in New England it's all 15-40.
So I go with what the local are using and have been using 15-40 for the last 8,000 miles.
Once I get into a hot climate again, may go back to straight 40w, but then may not.
While the engine has not changed in 40 years, nor the manual, the data has shown that multi weights have more advantages than disadvantages for all engines.