Adding Zinc to Oil?

[tirod]

Zinc has a recent history of being deleted from the spec in the SM oil. That's part of the additive package that makes up what it does, and the 5-15% of oil that does "wear out." It acts as a sacrificial friction reducer on bare metal surfaces.

Broken it, it doesn't do much. Cranks are nitrided, and run on bearings, it's new flat tappet lifters and rockers that get most of the scuffing. Nitriding the cam and lifters seems to do more, and ceramic faced lifters apparently don't even need to go back on the same lobe. NASCAR teams have been running those.

Zinc got dropped mostly because it contaminates cat converters. Adding zinc back in for a motor already broken it doesn't do much. There's a lot more discussion over on bobtheoilguy from a few years ago that details a lot of this.

As for mixing viscosities, in terms of actual oil, it doesn't care. A 50-50 mix of 5-20 and 10-30 will result in a net viscosity of 7.5 - 25. It's just oil. The additive package from competing makers might be adversely affected - but until they print full disclosure, we can't tell. I can tell you touring an oil packaging plant in the '70s - Phillips 66 in KC, MO - there were at least 5 competing brands coming off each oil filling machine, and they sorted by brand after they were filled.

Net result -exactly the same stuff regardless of brand. Don't make too much of it.

As for buying high zinc oil, you could run Rotella 10-30 or something for diesel trucks, but a lot of that is still SM rated oil, which means it could be low zinc. You have to read the labels and understand the specs to be sure.

Don't get this confused with the simultaneous sale of badly made chilled iron lifters from the Far East back then. There's a lot of mixed reporting on the whole issue at the time, and home garage reports are a bit suspect over which was the actual cause, a soft lifter or no zinc. Considering most use assembly lubes, the initial scuff in over the first 500 to 1000 miles, and later a failure of a cam lobe, points to the lifter all along. We also have the fad of using high ratio rockers and high spring pressures adding to the load on the lifter face, jumping up the psi quite a bit. Probably too much of a good thing again, which is our habit.