Steps
- Locate the spark plug or plugs. They can be found by following the spark plug wire (a larger black or colored wire leading to the cylinder head). If there is more than one plug, make sure you write down or label each spark plug wire before you take it off. This is important, as on an 8 cylinder engine, you can easily forget which wire goes where.
- Clean around the spark plug before removing it. Any dirt that has built up around the plug will fall into your cylinder when you pull the plug out. Nothing should go into that hole while the plug is out. Make sure everything is clean. Don't leave small parts in a place where they could fall into the cylinder.
- Put your spark plug socket and ratchet handle over the spark plug and turn it counter-clockwise to loosen. It will be quite tight at first, but should come out easily after that.
- Take a look at the electrode end of the plug. Check to see if there is a carbon buildup on the electrode, or if the gap is filled with dirt. If it is oily, you may have worn rings. If the plug is tan, the engine is working properly.*
- Be sure that your replacement plug is the same size as your old plug. The threaded part should be the same length, and the threads should match. If you're unsure what plug to buy, take an old one with you to the store and have the counter person match it for you. Also, they may be able to tell you the correct plug gap for your application.
- Check the gap of the new plug. It should be within the engine manufacturer's specifications. Plug gages are available at your local parts counter, usually for a dollar.
- Insert the plug back into the cylinder head BY HAND at first. Make sure to line up the threads. If you can't get the plug most of the way in by hand, something is wrong. When the threads are lined up, you should be able to get the plug all the way in by hand.
- Tighten the plug with the socket and ratchet. You want the plug to be tightened to the torque specification indicated in a repair manual. Sometimes the auto parts store worker may be able to tell you the torque specification for your vehicle.
- Put the plug wires back on the correct plugs. They should snap on and not be easily pulled off. Check to see if they are worn or have cuts in the insulation. If they do, replace them.
Video
Tips
- A good spark plug socket has a rubber insert to hold the spark plug from falling out. There are two sizes: 5/8" and 13/16"
- Always replace all spark plugs at the same time.
- Always replace all spark plug wires at the same time.
- Before replacing your spark plugs, it is recommended to clean the engine at a car wash or in your driveway with a spray bottle of Simple Green, a brush and garden hose, paying special attention to the spark plug location areas of the engine. This will prevent dirt and grit from getting into the plug holes while replacing the plugs.
- Now would be a great time to perform a cylinder leakdown test or compression test while the plugs are out...
Warnings
- Leaving a spark plug loose in your engine can cause it to shoot out of the engine like a bullet. Consider the tremendous pressure that your engine produces in each cylinder. If the plug is loose, it will strip out go flying at a high rate of speed.
- Putting spark plug wires back on the wrong plugs will cause a poorly running engine, and may make you think you have bigger problems than you do. If you just removed plug wires, and now the car runs very roughly, you should re-check the location of the plug wires against a service manual to be sure they're in the right place.
- Get the right size plug. If the thread depth of the plug is too long, it may come in contact with your piston, which will cause catastrophic engine failure. Don't guess which size, ask your parts guy... He knows, or at least has a computer or book that does.
- If your engine has aluminum cylinder heads, the plugs must be replaced when the engine is cold. Installing plugs when aluminum heads are hot can cause the threaded area to crack.
- Make sure you gap your plugs to the specified gap, unless the plugs say DO NOT GAP. Do not try to change the gap of a plug that says do not gap.
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