> I'll pass on something I heard, don't know how true, but it was from
> a usually reliable source; Since the advent of roller lifters, the
> oil companies have been deleting the additive that keeps the cam from
> wearing out on the straight lifter type of engine. The only oils
> that still have it are those intended for diesel engines. There is a
> a designator (CD or something like that-I can find out if anyone is
> interested) that indicates the additive is there. The oil is
> available at truck stops - Shell has been recommended to me. Anyone
> know if there is any truth to the story?
There's a tiny kernel of truth to that, but most of the above is very twisted.
There is an additive containing zinc (zinc dialkyl dithio phosphate or something
like that, ZDDP for short) that used to be found in higher concentrations in the
better engine oils (like Valvoline). ZDDP really is something of a miracle
additive, but since it's public domain, no one advertises it. It forms a
microscopic film on the steel of the engine, that gets rubbed off first if there
is metal-to-metal contact; thereby reducing wear.
Unfortunately, zinc is a poison to catalytic converters, so the standards for
the amount of zinc allowable in gasoline engine oils have moved downwards
several times. As I recall, the current allowable standard is something like
1/3 as much zinc as Valvoline Racing oil used to have.
However, AFAIK there are no such restrictions on diesel engine oil (and the CD
designation indicates a diesel engine oil). That doesn't necessarily mean they
have more ZDDP, only that they are allowed to. I just did a quick check,
Chevron Delo 400 has .148% zinc while Valvoline racing now only has .13% ...
hardly worth worrying about, IMO. I didn't find a zinc content for Shell
Rotella, only the comment that it is going down in 2007.
OTOH, full synthetic supposedly has a much higher film strength to begin with
than conventional oil does, so should need the ZDDP less (since it only comes
into play after the oil film breaks down). Those big truck oils cost as much as
full synthetic, and after all have additive packages for diesel rather than
gasoline (they were already separate oils before the restrictions on zinc came
about). So while I can't prove which one is better, I plan to stick with
Valvoline full synthetic.
Randall
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