Changing a set of spark plugs is a task that always sounds like an easy job, because most of the time it is. Swapping out a crusty spark plugs for a freshly gapped set is one of the few routine things left to tune up on modern engines – with modern being a relative term around here. Problems start with certain engines and spark plug designs that can turn changing the spark plugs into everything but easy or money saving. Fear not. Spark plug disaster is the exception rather than the rule. A little research can prevent a lot of headache.
Fuel. Air. Spark.
The obvious task of the spark plug is to light up the fuel and air mixture when the piston reaches the top of its compression stroke. The resulting burn pushes the piston back down in the cylinder. So it goes. The less obvious function of the spark plug is to transfer heat away from the combustion chamber as a heat exchanger. The spark plug wicks combustion heat through itself into the metal of the hole it’s screwed into, and into to the engine coolant surrounding that metal. Spark plugs are rated from cold to hot based on the speed at which they can transfer heat away from the combustion chamber. At the correct heat range combustion byproducts burn away. The spark plug cleans itself!
Hot, No Wait Cold
Talk of cold and hot spark plugs is a somewhat counter-intuitive. A spark plug in the colder heat range transfers heat quicker. A spark plug in the hotter heat range transfers heat slower. Using a spark plug too cold in heat range can bring excessive temperature, pre-ignition, and in severe cases a melting of the plug electrode. Metal parts flying around in the combustion chamber are very bad. Using a spark plug that’s too high in heat range can cause crud to build up on the electrode, which can lead to decreased spark efficiency. For a great explanation of this conundrum (and others) with illustrations head over to NGK Spark Plug studio.
Choose Wisely
The right spark plugs are designed specifically to work with the engine they’re being screwed into. Spark plug manufacturers make this choice easy. Make. Model. Year. Engine. Presto! The next thing to check is the gap. While spark plugs come pre-gapped, it’s a safe bet to consult the service or owner’s manual for the correct gap and check with a feeler gauge before installing – with exception! Some newer and expensive spark plugs can easily be ruined if gapped. Do not attempt to gap Iridium or similar exotic tipped spark plugs. This warning or similar statement to this effect is often printed on the side of the box. All the junk around here works great with plain old copper core 1.49 each spark plugs.
Useful Things
- Spark Plugs
- Spark Plug Socket
- Extenstion and Ratchet
- Plug Boot Pliers
- Hand Tools
- Clean Rags
- Gap Gauge
- Anti-Seize Compound
- Di-Electric or Spark Plug Grease
- Rubber Hose [optional]
Gap and Replace Spark Plugs
Stop Before, Not After
While swapping out spark plugs is routine stuff, it’s one of those tasks that can and occasionally does go awry. If for some reason the spark plug doesn’t want to come out of the hole it’s screwed into by way of a mild counter clockwise twist, then stop. If your engine is one of those that has known issues with spark plug removal, then stop. It would be great if the engine didn’t need to be moved to remove one spark plug, or if the spark plug was designed not to break into two pieces upon removal and leave half of itself in the cylinder head. Fat chance! The internet or the forums are your friend. With any luck you won’t be the first one to discover bad news.
How Often?
There is no reason to swap spark plugs too often or wait too long. Every 30,000 miles is a ballpark for conventional copper core spark plugs, but keep in mind that all engines will have different requirements. Some newer vehicles will never require the average driver to even think about the spark plugs. If you have this kind of modern engine you’re probably not hanging out around here too much anyway! While swapping out your spark plugs is relatively simple, there are a few classic pitfalls. Follow along with the handy how-to gallery for everything we know. For everything there is to know about spark plugs, dig into this entertaining knowledge trove from NGK.
Where’s the part where you tell us how to install a helicoil after we strip out the original threads?
Over the course of dozens of cars and as many years I’ve never had that problem with spark plugs. Exhaust manifold studs and rusted suspension bolts are another story. Stay tuned for the right-angle drill edition of how to install a thread-sert or heli-coil.
Right angle drill…my wrists hurt just reading that. You know you’re hosed when you’re using the right angle drill. What about reading plugs? Some of us could use a refresher…
Now that I’ve got a relatively stable, 2-car garage, I’ve taken to throwing the old spark plugs in the boxes the new ones came in (works fine for my 4-bangers, a bit less tidy with my wife’s V6). I’ll write the date of the change and odo reading on the end of the box, then stick ’em up on an overhead shelf out of the way. This way, I don’t have to try to remember when I last changed them, since I just glance up every time I’m in the garage. Bonus: When I go to swap again, I can compare the current plugs to the previous ones for coloration, oil, etc. It’s not a sure thing, but it spares me those “Did they look this bad the last time?”
Right angle drill edition of heli-coil sounds interesting. It’s been years since I’ve coiled an exhaust stud. Never stripped a spark plug, myself, but just recently had to fix a head where the previous owner got a little carried away. http://www.tarmac-and-gravel.com/2009/07/how-to-install-a-helicoil/