The Service Manual for the 2005 Dakota has this warning:
The 4.7L V–8 engine is equipped with copper core ground electrode
spark plugs. They must be
replaced with the same type/number spark plug as the original. If
another spark plug is substituted, preignition
Champion, Autolite, NKG, Bosch, etc want to sell me platinum plugs.
What's the reason for the need for copper core?
I think I just figured it out. They literally do mean that the ground
(outer) electrode is solid copper. Copper is a very good thermal
conductor, so having that electrode made of copper lessens the
likelihood of pre-ignition because it will be cooled by a better thermal
connection to the cylinder head (cylinder head acts as a heat sink).
(To reply by e-mail, replace the last letter of the alphabet in my
A) it works better
B) Pt electrodes typically have one wire very fine and the other large.
Since a waste-spark ignition system depends on the plug not caring about
the polarity of voltage its fed, fine-wire plugs are a bad idea.
C) Did I mention platinum plugs are a waste of money?
Is this true of platinum plugs other than Bosch? I'm particularly
remembering autolites as having a very normal-looking center
electrode, with a platinum cap on it. Also, I thought it was only
coil-pack systems that drive half the plugs backwards -- for which
there are double-platinum plugs.
My experience with them is that they change spark plugs into a
non-maintenance item. I can't think of when I've inspected a platinum
plug that turned out to need replacing, and didn't have some other
good reason (a blown head gasket being the particular example I'm
thinking of) for failing.
Its not AS true of others. IIRC, Autolites have a center electrode maybe
half the size of their copper plug, but much larger than Bosch.
I think another poster probably hit on it- the 4.7 needs a copper
ground electrode that will conduct away heat faster after the combustion
Given that my recently-acquired Jeep had its installed-at-Chrysler in
late 1998 copper Champions in it when I bought it 2 months ago (with
120,000 miles) and they were only opened up to about .045 from .035 and
had no deposits at all to speak of, I'd say that its electronic engine
management that has turned plugs into a non-maintenance item. I replaced
the plugs, wires, cap, and rotor... and noticed NO difference in the way
the Jeep runs. It could probably have racked up another 50k miles on
Becca's Neon, on the other hand, which also had a little over 100K
miles when we got it, had plugs that were eroded to near uselessness.
It got double-platinums, but I'll never know how they wear since we've
now sold the car.
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