It might seem like a simple task to some, but spark plugs can often be overlooked during routine maintenance. Checking them is just as important as changing your oil. Not only do fresh, properly gapped plugs improve the performance of your engine, they can also tell you a lot about how your car is running. You'd be shocked to see how much build up you can find on your plugs-kind of like flossing your teeth. You do floss your teeth, don't you? The procedure is quick, easy, and you could save yourself a lot of money in the long run. Hell, if we can do it, anyone can, right?
1. Make sure your engine is cool before you start. You don't want to burn your hands or strip the threads on your aluminum cylinder head. | 
2. You'll need a ratchet, spark plug socket, and an extension. If you don't have a spark plug socket, you can either put tape on the inside of a deep socket or use your spark plug wire boot to pull out the plug after you've loosened it. |
3. A light brown spark plug tip means that your car is running fine: not too rich and not too lean. | 
4. There is an additive in unleaded fuel that leaves your plug tips a reddish brown. This is fine. |
5. If the spark plug tip is wet or really dark, you're running too rich, which means your car is running sluggish. Check your plug heat range, gapping and fuel system. | 
6. Little spots or a damaged tip means that your engine is detonating. This is very bad, to say the least. Check your timing, fuel system and quit using cheap gas. |
7. Sometimes the plug can just be worn down from regular everyday use as you can see in this picture. Just swap them out with a fresh set with the proper gapping. | 
8. A fouled plug is caused by short distance driving. Most cars run rich at cold start then lean out as the car starts to warm up. If you constantly drive your car before it reaches normal operating temperature, you'll foul your plugs so you need to swap them for a new set with the right gapping. |
9. When your plug looks like this, it means you're car is running too lean. This can be corrected with cleaning your fuel system out or retarding your ignition timing a bit. | 
10. A lot of weird clumpy stuff built up around the tip shows that you are burning oil. It's either coming from the piston rings or valves. |
11. If your plug looks like this, you've got more problems than you could possibly imagine. Go find a good mechanic to further diagnose your engine issues. | 
12. When swapping in new plugs, check the gap on them (use the manufacturer recommendations) with a gapping tool. Of course the gap size can vary if you're running aftermarket parts. Hand thread the spark plug first so you don't strip the head on the way in. |