My manual for my 1950 Cadillac calls for SAE 20, which you can’t really find anymore. Not only that, but the Zinc or ZDDP content in modern oils is apparently much less, and this can be detrimental to an older engine I’m told.
I’m trying to figure what the best oil viscosity is to use for the Cadillac.
On classic car forums I’ve got people chiming in across the board using just about every dang viscosity available in substitute for the straight weight they used to use back in the day. Its a little annoying because I cant find good reasoning to use one or the other. I’ve heard 10w-30, 10w-40, 20w-50, 15w-40. Its like people just choose whatever they feel like!
What would be the safest, most correct oil to use these days for a car that called for SAE 20?
One person mentioned getting Accel oil from walmart because it has an SF rating (for cars built prior to 1988) and has zinc in it. But there was only 10w-40 available. I’ve also heard of using diesel rotella 15w-40 for the zinc content. Seems like people are just choosing the high zinc content oils available and the viscosity is secondary.
So what is it?