AD100 oil vs 20/50
 

For years I've been filling planes up with AD100 and AD80 oil. Suddenly the oil shed is full of 20/50.

Is it the same oil rebranded or has there been a change of opinion on oils to put in planes. Does it do something different?

Putting in the same stuff we put in cars 20 years ago is not as sexy as 'Special Aeroplane Oil' and demeans the kudos of what we do.

Anyone got an explanation?

There's one measure of viscosity based on SAE standards(Standard Automobile Engineer) and simply another terminology for viscosity in Commercial Grades and Military Grades. The equivalency is as follows:

SAE Com Mil
20 55 1040
30 65 1065
40 80 1080
50 100 1100
60 120 1120

The SAE50 you'd use in your car is equivalent to the straight mineral oil Shell 100 you stick in your aircraft. (or Shell W100 ashless dispersant grade which has various additives).

A multiviscosity grade eg SAE20W50 that you'd probably put in an old classic car is designed for opposed piston engines to be equivalent in terms of viscosity/temp performance to Commercial Grades 65, 80 or 100.

Best speak to whoever is filling your oil shed...

Thanks for the reply Vedeneyev, very interesting.

Tacpot, hmmmmm...