Multi-Vis Oils Less Lubricating?

[Nomen Nescio]

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?

 

[Guest]

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".