Question:How hard is it to change a set of spark plugs myself?
Answer:There's no easy answer to this question because
it depends entirely on your vehicle and your ability level. On
cars and trucks where the spark plugs are easily accessible (most
four cylinder and straight six cylinder engines), most people
should not have any trouble replacing the plugs. All you need
is a deep socket (13/16 or 5/8 inch), a ratchet wrench and maybe
an extension and a swivel. But on many vehicles, the plugs are
buried and are extremely difficult to reach. These include most
front-wheel drive cars and minivans with transverse (sideways)
mounted V6 engines. The rear-facing bank of plugs on these engines
can be very difficult to reach. Most accessory-laden late model
vehicles with V6 or V8 engines also have at least several plugs
that are extremely difficult to extract. Full-size vans are probably
the worst in terms of plug accessibility. But if you have the
patience of Job and the dexterity of an octopus, go for it.
PLUG REMOVAL
CAUTION: Do not attempt to replace the plugs on any engine
with an aluminum cylinder head while the engine is hot. Doing
so risks stripping the plug treads in the head. If this happens,
it will require repairing the threads in the head with some kind
of insert.
Also, most experts recommend applying a drop or two of anti-seize
compound to the threads on the new spark plugs before they're
screwed into an aluminum head. This will minimize the risk of
thread damage the next time the plugs have to be changed.
The hardest part about changing a set of plugs (besides accessibility)
is often getting the plug wires off without damaging them. If
you jerk on the wire to pull it loose, you may pull the wire right
out of the plug boot or break the wire. So don't jerk on the
wire. Pull on the plug boot with a twisting motion to break it
free. Special plug wire pliers can also be used for this purpose.
Another problem you may encounter is a plug that seems to
be frozen in place. If it's been a long time since the plugs
were changed, rust and corrosion can build up on the threads and
make the plugs difficult to remove. That leaves you with a couple
of choices: forget about changing the plug and leave well enough
alone (which is not a good choice if the plugs need changing or
are fouled), take your vehicle to a professional and let him deal
with the problem, or try to get it out and take your chances.
Trying to loosen a frozen plug involves a couple of risks.
One is stripping the threads in the plug hole. The other is
breaking off the plug. If you cock the plug socket while pulling
on the ratchet handle, you can easily crack or break the plug
insulator. Now you've got a broken plug and a dead cylinder.
If you can't get the plug out, the head may have to come off
so the plug can be drilled out! Fortunately, this kind of thing
doesn't happen very often -- but it does happen.
One way to minimize the danger of breaking a frozen plug is
to apply heat with a propane torch, then remove the torch and
squirt penetrating oil around the base of the plug. Give the
oil some time to work, then try the plug again.
READING THE PLUGS
Assuming the plugs all come out without a hitch, the next
step is to "read" them. Reading the plugs means looking
at the color and nature of the deposits on the electrodes. This
can help you detect problems that may be causing the plugs to
foul or other driveability or performance problems.
- Normal plug deposits should be gray to brown and flaky.
- The presence of thick, oily black deposits would tell you
your engine is burning oil (probably due to worn valve guides
and/or rings and cylinders).
- Electrodes coated with black fluffy deposits would tell
you your engine is running rich (getting too much fuel). This
may indicate a problem with the carburetor (often the choke),
the oxygen sensor or even the coolant sensor (a bad coolant sensor
can make a computer-controlled engine run rich).
- If the plug electrodes have hard, yellowish deposits, dark
specks or are cracked, your engine is running lean (not enough
fuel), the plugs are running too hot (maybe because the plugs
are the wrong heat range for your engine), or the engine is experiencing
detonation.
INSTALLING NEW PLUGS
Refer to your owner's manual or a reference manual to determine
the type of plugs your engine requires. Any brand of plug should
be okay.
CAUTION: Do not substitute a different plug number from the
one listed for your engine if the store does not have the exact
plugs you need. Spark plugs come in different heat ranges, reaches
and thread sizes. Using plugs with the wrong thread size or reach
may cause damage if the plug extends too far into the combustion
chamber and hits a valve or piston. Using a plug with too cold
a heat range for your engine increases the odds of fouling. Using
a plug with too hot a heat range increases the risk of detonation
and preignition.
All new spark plugs come with pregapped electrodes. But this
doesn't mean the preset gap is necessarily the correct gap for
your engine. So don't install the plugs until you've looked up
the correct gap for your engine, measured the electrode gap on
the plugs and adjusted the gap as needed. A feeler gauge or special
spark plug gauge is needed to check the gap. If the gap is not
If your engine has an aluminum cylinder head, use a drop of
anti-seize on the plug threads when the plugs are installed.
(Anti-seize is not necessary on cast iron heads, but it won't
hurt anything and will make the plugs easier to change the next
time around.) When you tighten the plugs, go easy on the wrench.
Threads in aluminum heads can be easily stripped if you use too
much force. The plugs only have to be snug. Also, be careful
to hold the plug socket straight while tightening so you don't
break a plug.
