DeTomaso Mailing List: March 2000, Message #48

On Mon, 21 Feb 2000, Kirby Schrader wrote:
> I've had no less than nine, no... make that ten people who have 
> confirmed that they think platinums DO suck, they all have bad 
> stories and mostly similar stories to mine.
> 
> So...
> 
> Why do the 'very knowledgeable' dudes at the parts store swear by them?
> (probably don't use them themselves or they get paid a commission?)
> 
> Why are they still on the market if they're crap?
> (I know, marketing....)
> 
> What the hell are they made for if they won't work in anyone's cars?

The _original_ design Bosch Platinums won't work with a wasted spark ignition
system (where two cylinders share a single coil, which fires both cylinders'
spark plugs every time).  

The reason for that is that the teeny tiny platinum center electrode suffers
erosion from being fired (sparked) in the wrong direction.  Platinum resists
this erosion much more effectively than copper or steel (which is why
platinum-tipped plugs are employed by the manufacturers), but that little
tiny electrode simply has insufficient metal to be fired backwards for long.

Every time the spark jumps the gap on a spark plug, the spark carries a
_little_ bit of the electrode's metal with it (some of which gets deposited
on the other electrode).  In the case of the tiny center electrode on the
original design Bosch Platinums, there wasn't much metal to begin with
because they were designed for the spark to jump from the side electrode to
the center electrode.  However, a wasted spark ignition is always firing one
of the plugs backwards (by it's design).

Many (most) modern cars with distributorless ignition are using a wasted
spark so that they can use half as many coils.  That includes, by the way,
the Electromotive crank-fired ignition.

If you're not running a wasted spark ignition (either you have a
distributor, or one coil per cylinder like modern e.g. Beemers) then the
Platinums should work fine.  I've personally put a bazillion trouble-free
miles on them in numerous different cars in the past.  Nowadays most of my
cars employ wasted spark ignitions, so I don't use them anymore (and I
wasn't even aware the original design plugs were still available).

I think maybe some folks confuse those original design plugs with the modern
offerings... most of which have little platinum "buttons" on the electrodes
to resist erosion.

On the other hand, unless you have concerns about your plugs fouling, the
original design Platinums probably have little to offer you.

There are quite a few modern platinum-tipped conventional design plugs that
will provide very good longevity (without the anti-fouling characteristics
of the orignal Bosch Platinums) with any ignition system (including wasted
spark ignition system).

Oh, and by the way, many new cars come from the factory with platinum-tipped
spark plugs because the car makers need the plugs to last the full length of
the required emissions warranty.  In some cases (I know Ford does this on
some of their engines), they are only platinum-tipped on one or the other
electrode to save money (Platinum isn't cheap) according to the direction
the plug will be fired.  So be careful when you replace the plugs in a
modern wasted spark ignition car - if you get the plugs mixed up you will
have the platinum on the wrong electrode and it won't do you any good (and
eventually will suffer accelerated spark erosion).

-Andy

72 Pantera - Rocky             91 Miata - Steve                 96 A4Q - Rudolf
80 928 - Phantom        87 E350XL - Andylance (FOR SALE)       84 RZ350 - Sting