DIY Spark Plug Replacement
***DISCLAIMER: though changing spark plugs is a relatively simple task, you can do
expensive damage to your engine's cylinder heads by cross-threading spark plugs on re-insertion.
You can also get seriously burned by working on a hot engine. The Free Information Society, and the
author of this article, assume no responsibility for damage to your engine, or injury to your
Changing spark plugs can be a fairly easy task, or can be a real nightmare. It really depends on
the design of the engine, the engine placement, and the amount of room you have under the hood.
(boot). You can save a significant about of money by doing it yourself, if you don't mind getting
I will be changing the spark plugs in a 1995 Mercury Villager mini-van. The particular 3.0 V6
Nissan engine in this van is the same one that was in several Nissan vehicles, including the Maxima
and the Quest. But, the instructions and hints are basically the same for all gasoline powered
internal combustion engines.
Generally, most auto manufacturers recommend changing spark plugs every 30,000 miles.(about
48,000km) I think that it has been about 50,000 miles since I last changed plugs in this vehicle.
First, you need to gather the items you will need for the job. Of course, you will need spark
plugs. Today, they usually come in packages of two, so you will need two, three, or four packages,
depending on how many cylinders your engine has, four, six, or eight. If you have a 5-cylinder
BMW, you may have to buy one too many. You will need to know the year of your car and the engine
size. If you buy the plugs from an auto parts store, you tell them what your car is and they will
hand you the plugs. If you buy them from a department store, you will usually have to look them up
yourself, usually from a book. Double check yourself to make sure that you are getting the correct
There are several grades of plugs, the cheapest will usually suffice. These are the next grade up.
There are also some very fancy high-performance plugs. I have tried a couple of brands, and yes,
I could tell the difference. Being a cheap bastard, I usually refuse to pay the 3-5 or so times
more that they cost over the cheapest.
There are two different sizes of spark plug wrenches, 13/16ths, and 5/8ths, and you will need the
correct one for your plugs. I don't know if the plugs are metric outside of the US and use metric
sized wrenches, so if you live outside of the US or Canada, you will have to do some research to
determine what wrench you will need.
I highly do not recommend your using a regular socket to change spark plugs. As you can see in the
photo, a spark plug wrench has a rubber boot inside of it, to hold the plug in the socket. This
boot is very important, as you will see later. Spark plug wrenches also have a hexagonal end, to
use a wrench on them in case you are in a tight spot that a ratchet wrench won't fit in. I have
occasionally had to do this.
You will also need a ratchet wrench, and extension(s). Depending on the engine, you may need
multiple extensions. Yes, I will need all of these, as you will see.
If you have some plugs on the back side of your engine, the universal joint is priceless. It can
be used in combination with other extensions. Having two wrists instead of one often helps,
You will also need a feeler gauge, to ensure that the spark plug is gapped properly. This
information is usually found in your owner's manual. If you don't have the owner's manual for your
vehicle, the information is also found in the book that you looked your plugs up in. If you
already own a feeler gauge, check to make sure it isn't rusted beyond use, they rust very easily,
especially when stored in a shed or car. LOL. Mine was, and I didn't feel like traveling back to
the store to get one. To be honest, probably 90% of the time, my plugs have been properly gauged
from the factory.
Another couple of things I might recommend, is "boot lube" a grease to put into the spark plug wire
boots. Also, "anti-seize compound" to put on the spark plug threads comes in handy. This is a
heat-resistant grease that normally contains graphite. You will see in later photos that the
threads on my spark plugs were rather rusted. Like for the feeler gauge, I didn't want to go back
to the store.
First, you should find a good place to perform the task. I recommend a shaded place (if its hot
out), on a smooth surface in case you drop anything and also in case you have to crawl under the
vehicle to reach any back plugs. In case of the latter, I highly recommend if you don't have any,
buy, borrow, or rent, a good floor jack, some ramps, or jack stands. It just isn't safe to use
the jack that came with your vehicle if you are crawling under it. Though, I must admit, I usually
do...even though I have ramps and a floor jack.
Also, I usually attempt to do this at a time that there are no kids, wife, or neighbors around, as
I tend to "cuss like a sailor"...especially when working on vehicles. I also usually keep my small
dogs away, as something usually pisses me off enough to kick one...and I don't want a visit by PETA
or the ASPCA.
Before you begin, I highly recommend you take a few minutes to evaluate the placement of your spark
plugs, especially if you will need to use the vehicle to return to the store for something you
failed to get initially. On this particular engine, the spark plugs are all located on the top of
the engine block, and no components need to be removed to get to the plugs. To be honest, this is
the first engine I have owned that the plugs are located in such a convenient location, and I
really thank the Nissan engineers that had the foresight to put them there. If the plugs were
located on the side of the engine block, the "back" plugs would have to be removed from under the
vehicle, as in this particular configuration, it is impossible to get to the backside of the
If you will notice, two of the "back plugs" are located under the fuel injection manifold. It is
about a foot between the top of the FI tubes and the spark plugs, hence the need for all of the
ratchet extensions in the earlier photo.
WARNING>>>Before continuing, I highly recommend your letting the engine cool for a few
hours. If your plugs are located on the side of the engine block, you WILL touch the exhaust
manifolds, and they are definitely the hottest part of the engine. You are ensured to get burned
by working on a hot engine.
While you are letting the engine cool, I recommend you remove all spark plugs from the packaging,
and check the spark plug gap on each. Take the blade (or combination of blades) on the feeler
gauge that matches the recommended gap width, and attempt to insert it between the center electrode
and ground electrode. The blade(s) should touch each electrode, but move freely between them. If
the gap is too narrow, I usually use the frame of the feeler gauge to GENTLY pry the ground
electrode (curved outer part) from the center electrode. If it is too wide, I usually use the end
of a nylon screwdriver handle to VERY GENTLY tap the end of the ground electrode towards the center
Though spark plugs are fairly durable, be careful not to drop them, if the ceramic insulation gets
cracked, or the center electrode chipped, the plug is usually ruined, and you can close the gap
that you have just properly set.
So, now our engine has cooled, our plugs have been gapped, we have all of our necessary items, so
let's get started. Start wherever you wish, I recommend starting on one end or the other.
Actually, I usually start with the easiest plug to reach. Carefully remove the spark plug wire
from the plug. You may have to rotate it some to unstick it from the spark plug...it will probably
be stuck, considering that the plugs get over 1000F. Take your time, don't use brute force. If
the metal contact on the spark plug wire happens to pull off of the wire and stays on the plug,
don't panic....I will put instructions at the end of this article on how to repair it. REMOVE ONLY
ONE WIRE AT A TIME!!! It is pretty easy to get the plug wires mixed up on some engines, and the
wires MUST go back on the cylinder they came from. Though it is not that difficult to determine
the proper firing order if you get the wires mixed up, it is totally unnecessary to remove more
than one wire at a time.
As you can see, this plug is somewhat rusted, though the engine design with the plugs on top is
convenient, it is possible for moisture to pool up around the plugs, causing them to rust. I wish
I had used the boot sealant the last time I changed plugs, the upper part of the center electrode
being rusted isn't a good deal. Place the spark plug wrench on the plug, make sure it is seated
well, and loosen the spark plug. As most bolts, it loosens by being turned
Once the spark plug is loose, gently pull the socket away from the engine, taking special care that
the plug doesn't fall out of the wrench. There is always stuff to bump the wrench against, so take
special care, especially in my case, where the plugs would fall back into the hole.
Now that I have a plug out of the engine, I take a second to observe the plug. It was just time to
change plugs, notice the deterioration on the center electrode. I have changed plugs that were
much worse...once where the ground electrode was nearly gone. I have no idea how the plugs were
actually firing, but actually, the vehicle was running fine.
Take a look into the plug. This is how a plug looks from a well running engine. Actually, I am
impressed, this engine has over 195,000 miles, and though I fully know how to properly maintain an
engine, I seldom do. I am a little surprised that there wasn't a little carbon buildup, as the
plug wires were in dire need of change, actually arcing, causing the engine to miss. The slight
red color is from gasoline additives. If your plugs don't look like this, google "spark plug
analysis" and you should easily find a site that has photos of various engine problems that you can
troubleshoot by "reading" your spark plugs.
Next, if you opted for the "anti-seize" grease, apply a small amount to the last few threads.
Then, gently place the spark plug into the wrench. Make sure that it is seated into the rubber
This is the hole that you are going to place the plug into. There are usually obstacles in your
path, so you must be careful not to knock the plug out of the wrench. Unfortunitely, you usually
cannot see the hole that you are headed towards. This is the hardest part.
Be careful....remember, if you bump the ground electrode, you may close the gap....
Now comes the trickiest part. Usually, the hole is at some kind of angle. You may have to play
around getting the plug into the hole, and putting the extension at the correct angle. Once you
are there, HAND TIGHTEN the plug for several threads. If you are met with resistance, back the
plug out and try again. This is no place to act macho or use brute force. You may have to
slightly vary the angle. DO NOT touch the ratchet until you have the plug hand tightened at least
halfway into the hole. CROSS-THREADING THE PLUG WILL DAMAGE YOUR HEADS!!! If you don't know what
a "Heli-Coil" is, you don't want to find out in this way.
Insert the ratchet on the extension, and tighten (clockwise) until you can't turn anymore without
force. Usually, at that point, I use two hands on the ratchet, and tighten a tiny bit more. Here
again, don't use brute force...remember what I said about the "Heli-Coil".
Next, I usually take the old spark plug, put a small amount of the boot compound on the tip of it,
and smear it around the inside of the spark plug wire boot.
As you can see, I put far too much in this one...get a Q-tip and get the excess from the
Finally, replace the spark plug wire. You should feel (and not hear) a "click" when the contact is
seated properly on the spark plug tip.
Repeat the above instructions 3, 5, or 7 times, depending on your engine, and you're done.
Repairing a broken spark plug wire....
I promised that I would show you how to repair a wire that the connector has pulled off. Ok, you
are pulling a wire from a spark plug...and the connector remains on the spark plug. Remove the
connector from the spark plug, and push the wire through the boot, exposing a few inches of wire on
the spark plug end of the boot....
Hmmm....this is a very high quality connector...you won't pull one of these off... Oh well, I can
work with this. You see the crimping on the connector...most connectors only have one or two of
these. If the connector is well stuck on the spark plug, the wire can pull out of the
First, open the crimping with a flat-head screwdriver, or a pair of needle-nosed pliars. You won't
have the problem I had, 'cause the wire won't be there. Oh well, what's a little blood for the
cause of free information....
This is how the end of the wire should look before replacing the connector. You may have to cut
away some of the insulation to expose some more core wire. Just be careful...don't cut the core
wire. The spark plug wire should be long enough to give you a little slack to do this, you
shouldn't have to cut more than around 3/4" of insulation.
The core wire should lay against the connector...place the wire between the crimping....
close the crimping with some pliers.......
That's it...push the connector back into the boot.
Article written by Frank Stroupe
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