Martin McGowan wrote:
Snakey wrote:
"Phil Kyle" wrote in message
snip.

Bomber Command used to have a "spark plug " crew attached to every
squadron, whose duty was to clean, gap, test and stuff 'em back into
the aircraft. I think you'll agree that was a fairly critical
application?

snip
Snakey


yes a critical application, that was why the Merlin engine had two spark
plugs per cylinder, each fired from a separate magneto. In the section
above there was one important stage left out. namely ditch the rejects
after test failure, and failures there were. Spark plugs do fail, and
they also degrade. I used to have to record all fuel used against miles
driven for accounts purposes and as an experiment i changed the spark
plugs separately to the service(I serviced my own vehicle) new spark
plugs gave me about 2 MPG increase tank full to tank full, replacing
standard with high efficiency plugs gave me just under 3 MPG increase. I
had my own small sand blasting kit to clean my plugs but i still had
reduced efficiency on old plugs. Spark plugs will go on for multiple
thousand miles beyond nominal replacement intervals, however there is a
penalty in reduced fuel economy.

I also used Teflon additives which gave a 1 MPG increase or thereabouts.
that was a use once and it lasted for about five oil replacements.
Martin McGowan

Strangely enough, my brother in law who does about 60K miles a year in a
diesel, reports a similar loss in economy before a service..my guess is
clogged air filters.