Why is it aircraft engines specify a single weight oil, i.e., SAE 30, not
>mult-vis oils? This is mysterious to me because aircraft engines must be
>started under varying temperatures just the same as cars.
>
>Once started and warmed up, automobile engines operate at a more constant
>temperature than do aircraft engines. If operating temperature would be
>the criterium, then car engines would be better served than airplane
>engines, yet we see mult-vis the rule for autos, but single weight for >airplanes.
>
>Could it be that the multi-vis additives somehow detract from the
>lubricating qualities which are better in single weight oils? On the
>contrary, could it be that most aircraft engines predate multi-vis oil and
>were certified for the then available oils which were single weight? There
>are multi-vis aircraft oils, so perhaps later engines were certified with
>multi-vis oils and the argument of superior qualities does not apply. >
>Also, I wonder why aircraft multi-vis oils are labeled for aircraft but not
>cars and vice versa. Isn't SAE 5W-30 the same whether it is poured into an
>aircraft engine or a car engine? Why is aircraft oil specially labeled and
>costs more than car engine oil?
Partly because it is an "ashless dispursent" oil, and partly because it has to deal with high lead content. - among other things, like paying for lawyers etc and the cost of "certification".