Dear Ray &
Tom,
I have a '97 Nissan
Sentra. I changed the spark plugs at 30,000
miles and just
did it again at 60,000.
The owner's manual says the spark plug gap
should be between .039 and .043 inches. I
set them at .040 and the car runs fine. I
checked the gaps on the old plugs I pulled
out, and they were between .050 and .060 --
WAY off! But the car had been running fine.
How important is the gap? -- Daniel
Ray:
Well, as you've discovered, Daniel, not that
important! Most cars will run fine, even
with the gap pretty far off.
Tom:
And in your case, what probably happened was
that the plugs burned down to .050 or .060
from their original settings. That's what
happens to old plugs -- the metal in the
electrode and the tip wears down from all
that firing. And that's one of the reasons
you replace old plugs.
Ray:
At some point -- it may have been at .070 or
.080 in your car -- the engine would have
developed a miss because the gap would have
gotten so big that the spark could NOT jump
it. And if you had other problems -- like a
weak coil or bad spark plug wires -- that
miss would have developed sooner rather than
later.
Tom:
The gap recommended by the owner's manual is
the optimal gap. That's where the engine
runs most efficiently. But in modern cars
with otherwise healthy high- energy ignition
systems, within 10 or even 20 thousandths of
an inch either way, most spark plugs will
usually fire well enough so that you won't
notice any difference in performance.
กก |