How to check spark plugs?

When To Change the Spark Plugs?

This depends on the type of spark plugs your vehicle is using. Spark plugs should be replaced at the vehicle manufacturers recommended intervals, but may have to be replaced sooner if they are fouled. On older vehicles, the replacement interval is typically 30k-45k miles (48k-72k km). On newer vehicles with platinum plugs, it may be as high as 100k miles (160k km). But short trip, stop-and-go city driving as well as extended idling can shorten the life of any spark plug.

*For standard spark plugs, Denso recommends regular replacement every 15k-20k km.

If you are experiencing a drop in fuel mileage, rough idle or lack of engine performance then you might want to change the spark plugs earlier.

If your vehicle is using spark plug WIRES, those wires usually wear out about 60k–70k miles (96k-112k km) and cause an engine misfire usually under heavy acceleration or pulling a trailer. It is recommended to change the wires AND the spark plugs at the same time.

Can Old Spark Plugs be Cleaned?

Technically, yes, you can clean spark plugs, however, in most cases it’s not worth it. It is not recommended for a number of reasons.

Ultimately, you won’t get the same performance from a cleaned plug as from a new plug. Electricity discharges best from sharp edges. A used plug will have worn edges, and cleaning may contribute to the wearing.

If you insist on trying to clean anyways, the cleaning procedure is below:

  • If the firing end is wet, make sure to clean the plug with a quick drying cleaner such as contact cleaner or brake cleaner.
  • Sand blast the spark plug using low air pressure and a dry compound.
  • Completely blow all sand from the plug.
  • Clean the threads using a wire brush.
  • Re-Gap to your vehicles specifications.

NOTE: Insufficient cleaning of a spark plug may lead to its failure in a very short period of time. Clean the spark plug thoroughly to avoid problems later. Remember, if a plug is fouling, its usually a result of engine side factors or incorrect heat range selection.

How Long Do Iridium Spark Plugs Last?

A traditional iridium plug such as a Denso IK20 or NGK ZFR6FIX-11 both have iridium center electrodes, however the ground electrodes are a traditional nickel construction. The ground electrode will wear out first. Typically you can expect 50-80k miles (80k-128k km) on an iridium plug. But plug manufacturers have to temper their projections as driving conditions and motor modifications differ. Additionally, because gradual wear will “round-off” firing points over time, the concentrated firing power and voltage requirement benefits will be reduced. Therefore, NGK gives them a life expectancy of 40k-50k miles (64k-80k km) and Denso assigns a recommended replacement interval of 30k miles (48k km).

Both Denso Iridium Racing plugs and some NGK Iridium Racing plugs have iridium center and a platinum ground electrodes. If installed in a regular engine, they would likely last longer than most people keep their car (barring any motor problems that can cause premature plug death). But, these usually come in heat ranges too cold for an unaltered motor and are usually used in racing applications where all bets are off.

For the traditional automotive market, the longest lasting plugs are the Denso Long-Life Iridium and NGK Laser Iridium series, which have iridium center and platinum tipped ground electrodes. These OEM style plugs typically have special features designed for a specific engine and last 80k-120k miles (128k-193k km).