On 23 Nov 2020 22:17:27 -0000, Scott Dorsey wrote:

> Engines with flat tappet cams will benefit from an oil with higher levels
> of ZDDP. As a consequence, many people with older cars use either an oil
> designed for diesel engines with high ZDDP, or use an additive with extra
> ZDDP. This was discussed extensively in this group twenty years or so back.

Hi Scott,

Thanks for that information about zinc dialkyl dithiophosphate (ZDDP),
which contains both Zn & P, neither of which is good for a cat.

I had never even heard of ZDDP until today, but the guy I just spoke to at
Chevron (1-800-822-5823) mentioned that it's what is both making it good
for the diesel engines, but bad for catalytic converter gas engines.

He did say it's a longer-lasting better oil for gasoline engines that do
not have the problem of passing a smog check (he made it a point to ask if
my state has smog, for example).

So if it wasn't for the cat, it would be a "better" oil than a conventional
gasoline engine oil (everything else being equal).

He did mention though that it's not "synthetic" by Chevron's definition,
but that it uses "synthetic technology", and hence the "isosyn" label.

The end result is that it's a good oil apparently, for diesels, and it's
even a better oil for older gas cars that don't have catalytic converters,
and, even for newer gas cars that do, as long as the cat isn't smog'd
periodically (assuming the viscosity is what you want).

But it's just not a good choice for modern gas engine vehicles with cats.