On Mon, 2008-03-10 at 08:47 +0000, buchananautomotive wrote:

> ZDDP and moly , but I must admit I am not a big fan of the much
> larger amounts of detergent in the diesel oils for the use in petrol
> engines ( I am just not at ease with that bit )( I am a bit fussy ).
>  Regards. BB.

This paper on ZDDP, based on research conducted by N.J. Mosey, T.K. Woo,
et al, at the Universities of Western Ontario and Ottawa (which was
brought to the attention of the list by Bruce B), states on page 8:

> 3.8. Effect of detergents
>
> Fully formulated engine oils contain additives other
> than ZDDPs, such as detergents, dispersants and fric-
> tion modifers. It is imperative to understand the effect
> of these additives on the efficacy of ZDDP. Dispersants
> alter the solution chemisty of ZDDPs [50,51], while fric-
> tion modifiers have little effect on the AW properties of
> the films [52]. Detergents, on the other hand, alter the
> chemical composition of the films, affecting AW per-
> formance [45,53,54]. Common detergents contain cal-
> cium ions, which are incorporated into the ZP film by
> replacing Zn. On iron-based materials, this increases
> wear compared compared to that observed when ZDDP is used
> alone [45,53].

See http://www.apmaths.uwo.ca/~mmuser/Papers/TL05.pdf

So think carefully before you choose a detergent-heavy oil which is not
intended for use in gasoline engines. Porsche has never recommended
diesel oils for the 928, even when it was doing so for the 911. I
suspect that oils are far more specialised than they were back then.