Engine Repair

How to know when to Replace Spark Plugs

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"How to know when to Replace Spark Plugs"
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Along with changing your oil, replacing spark plugs is probably one of the easiest maintenance tasks for the average car owner. Along with saving money in maintenance costs, a properly tuned engine will improve performance and fuel mileage providing additional savings.

Many car manufacturers now quote intervals between tune-ups of as high as 100,000 miles, or more. However, in order to accomplish these long periods between servicing they usually adjust the performance of the vehicle through the computer controls in the vehicle. Even such vehicles can often benefit from changing the spark plugs more often.

In order to replace your spark plugs, you will usually need a very limited amount of tools. A spark plug wrench or a ratchet with a socket to fit the spark plugs on your vehicle is often all that is needed. Most spark plugs sold today have the gap, or the space between the electrodes, preset. If the plugs you buy require the gap to be set you will also need a feeler gauge and a gap setter. Beyond that, all you should need is a rag or two.

Especially on newer cars where the spark plugs may be difficult to access, you may wish to have a service manual for your vehicle. Popular manuals from Chilton or Haynes are available for most all vehicles sold in the United States and will cover the necessary information. Such a manual can give you tips on your specific vehicle to make the task easier. Be certain to read the safety information at the front of the manual.

To replace the spark plugs you should work on one cylinder at a time. If you try to do them all at once you increase the possibility of crossing up wires between cylinders. This will make your car run worse than before, if it even will run, and end up turning what should be a very easy job into one that is much more difficult.

When you open the hood of your vehicle you will see the wires leading from the distributor to the spark plugs mounted in the engine's heads. There will be one wire and one spark plug for each cylinder. By following the wires to the plugs you can easily determine the difficulty of the job. If you have easy access to each spark plug the job won't be too difficult.

To remove the spark plugs follow the wire to where it leads at the top or side of the engine. You will notice a boot that fits over the spark plug. Grasping the top of the boot firmly you pull the boot from the plug. Never pull on the wire. Sometimes, over time, the boot will stick to the porcelain on the plug. If that happens, twist the boot until it breaks free and it should slip right off.

Clean around the plug with a rag as best you can to prevent debris from falling into the cylinders. Then place the wrench over the plug and turn counterclockwise to loosen the plug. When the plug is loose, remove it from the engine and set it aside. You might want to look at the plug to identify any discoloration or residue. If you see anything other than a tan coating on the base of the plug or the electrodes, that could indicate more serious problems with your vehicle.

If the new plugs don't have the gap preset you need to set the gap now. Insert a feeler gauge between the electrodes to measure the size of the gap. If you have a blade-type gauge you will insert one or more blades that add up to the thickness you want to measure between the electrodes. If you're using a round, wedge-style gauge, insert the gauge between the electrodes and rotate it until it is tight to measure the gap.

If the gap is too small you will use a gap-setting tool to adjust it. Usually your feeler gauge will include something with a small notch that can be used to grab the outer electrode and bend it out to open the gap. If the gap is too wide, lightly tap the outer electrode on a wooden workbench or against a wooden block to close it.

When you have the gap set you are ready to install the plug. Insert the plug into the hole and rotate clockwise with your fingers or wrench. You should never have to use any significant force to start the plug into the hole. If the plug feels tight it is likely that you have the threads crossed and forcing it can seriously damage your engine, especially engines with aluminum heads. If that happens rotate the plug counterclockwise until it feels as if it is seated properly in the hole and try again by rotating the plug clockwise.

Continue to rotate the plug until it is finger tight and you can no longer turn it by hand. This should take several turns to get the plug properly seated in the hole. When you can no longer turn it you should tighten it with the spark plug wrench. You shouldn't have to turn more than one quarter of a turn additional for final tightening.

After the plug is tightened into the hole place the wire back onto the plug. Once you've got the first plug replaced, move on to the next. Continue this, one by one, until you have replaced all of the spark plugs.

The first time you do this it might take a bit of time. Set aside an hour or two on a nice day. After you've done it a few times, however, you should be able to replace all of the spark plugs in your vehicle in just a few minutes. And, that few minutes can save you quite a bit of money over having this done at the shop and encourage you to replace your spark plugs more often. The additional savings that will come from improved fuel economy will more than justify the time and few dollars it costs to do the job.

More about this author: Keith Hamburger

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