Articles & Tips

Automotive Spark Plug Service Life & Maintenance Practices

The spark plug is the fire starter of your engine. Without properly working and cared for spark plugs how can you expect your vehicle to drive smoothly drive down the road or highway and give you adequate and acceptable miles per gallon of gasoline fuel driven? Few motorists give their spark plugs short shift - that is until their vehicle won't start in the dead of a country Singapore or their fuel usage is just horrendous. So goes life and the treatment of spark plugs in automobiles.

Spark Plug

Spark plug service life can vary overall a great deal depending on such factors as automotive engine design and designs themselves, type of ignition system installed and used ( electronic ignition or older types of points and breaker points), type of service the vehicle is used for generally , driver habits and even type of fuel used.

Under extreme cases, some sparking plugs may require replacement at 5,000 miles (equivalent to 8,000 kilometers). Others may last well beyond the often recommended replacement intervals of between 15,000 to 30,000 miles (that is 24,000 to 48,000 km) for newer more modern, and more popular on the road - electronic ignition system types.

In deciding whether to clean and reinstall or replace the plugs, the mechanic or do it yourself, the mechanic should weigh the costs and time of service for cleaning, filing and gap the plugs in remains of useful life left for the units at hand.

Overall - and not only for reasons of reliability and service, but it is also often an automotive truism based on year and miles of mechanic's experience and experiences that unless the plug or plugs are in truly sound condition then it usually the best choice overall to spring for new plugs. Costs for replacements are usually quite reasonable especially in this day and age of high fuel and gasoline costs.

What though are recommended spark plug cleaning intervals?
It can be said that when spark plugs receive periodic cleaning and gapping that they will overall function better and will last longer - both in terms of time and miles distance. Generally, it would be sound to say that a reasonable course of action is to have plugs cleaned and inspected in the ranges of approximately every 10 to 15,000 miles (equivalent to approx 16 to 24,000 km in metric terms.)

How do you as a mechanic - either amateur or professional examine spark plugs? A careful study of the spark plugs is helpful in determining engine condition, plug heat range selection and trouble resulting from operational conditions.

Spark Plug

In normal cases how does a spark plug appear then? It can be said that a spark plug operating in a sound engine, at the constant temperature will have some "gray deposits." Deposit color will range from tan to gray in appearance and appearances.

Electrode gap will show growth from about .001 (0.025 mm) per 1000 miles driven, but there should be no evidence of burning what so ever.

Features to look for and exhibit in pathological spark plug appearances and engine situations include - fuel fouling, oil fouling, splashed fouling, aluminum throw off and lastly what is termed in the automotive trades "scavenger " deposits.

How to Remove and Inspect Your Car's Spark Plugs

Because the plugs represent a critical part of your engine's operation (without the spark, there can be no combustion), it's important to change them when they show signs of wear. Neglecting to do so will result in declining performance. Below, we'll take you through the process of removing and inspecting them.

Gathering Your Tools And Locating The Plugs

In addition to a set of replacement spark plugs, you'll need access to a socket wrench, spark plug socket, and a few socket extensions. You should also plan to wear safety goggles to protect your eyes from debris.

Lift the hood of your vehicle, and look for wires along the top of your engine. They are made of rubber, and each is connected to a cylinder. If your vehicle's engine has four cylinders, you'll be able to see four wires. A 6-cylinder engine will have six wires, and so on. Once you have located them, you're ready to remove the plugs.

Removing The Plug Wires

A lot of people doing this for the first time are tempted to removed all of the wires simultaneously. It seems simpler to do so. The problem is the plugs in your engine's cylinders fire in a particular order. If, while replacing them, you inadvertently mix the wires and cylinders in the wrong order, your engine's performance may suffer. To avoid that problem, replace them one at a time.

Grip the first plug wire snugly, twist it and pull. It should come off easily, leaving the plug sticking out of the engine block. You'll see the plug's terminal (the topmost part) and part of the insulator exposed. The next step is to remove the plug.

Spark Plug

Removing The Spark Plugs

You'll need your socket to remove the spark plug from its housing on the block. Slip the socket over the plug (using an appropriate extension), and make sure the fit is snug. Then, attach the ratchet. Gain some leverage and turn it gently counter-clockwise. Apply a little pressure if the plug seems stuck.

Once you have removed the first spark plug, inspect its condition closely. It will provide clues regarding your engine's operation.

Checking The Condition Of The Plugs

There are several indicators that suggest possible problems. For example, look at the side and center electrodes (located on the opposite end of the terminal). Has black soot accumulated on the tips? If so, you're observing carbon deposits, which suggest the air-fuel mixture in the cylinder is running rich.

Do you see deposits on the electrodes that appear black and wet? If so, you see oil. This can mean a few things, but the most common are that oil is leaking past one or both of the valves (intake or exhaust) into the cylinder.

Sometimes, the center electrode will melt. This is more serious than oil leaks or a too-rich air-fuel mixture. A melted electrode might imply your engine is running too hot. It can also mean other things, but it is important to identify the cause to prevent expensive damage from occurring to the assembly.

Another item to note is the gap between the side and center electrodes. The spark that ignites the air-fuel mixture in the cylinder must be able to jump the gap. Over tens of thousands of miles and millions of sparks, the center electrode erodes. As it does, the gap widens. If you notice significant erosion, it's time to change the plugs.

Fouled, melted, or eroded spark plugs will eventually lead to engine performance problems. If your engine is behaving strangely, check the plugs and replace them, if necessary.


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