And by the 70s the recommended oils were multigrades. Same engine and filtration. Funny about that.
Quite true Trev,
But the 20w50 you bought back in the 70's is nothing like the 20w50 you get now days.
Half of the compounds that go into modern 20w50 were not even invented / discovered back in the 70's and half of what was in there then is now banned, like all copper compounds.
Next 20w50 is not a TYPE of oil, it is a VISCOSITY GRADE and that is all it is.
I can get Agtrans in 20w50 Rotella in 20w50 and Valvoline in 20w50 and they are all totally different oils.
You can get 20w50 without detergent additives or with normal levels of detergents or with higher levels of detergents.
Putting a high detergent oil into a BSA prevents the oil tank sludging large particulates out of circulation.
If an oil ank has the outlet at or very near the bottom then it is a resevior .
If it has the outlet higher up the tank it is a settleing tank