How To Read Spark Plugs

Both the fuel mixture and the ignition timing result in coloring of the spark plug s porcelain and ground strap.

How to read spark plugs. You will likely see one of the following conditions. The 5th position number stands for the heat rating. Follow the steps below to learn how to read your carâ s spark plug. The 6th letter identifies the thread length. To read a spark plug start by checking the color since an undamaged spark plug will be light grey or possibly tan.

Dark coloring such as heavy black wet or dry deposits can indicate an overly rich condition too cold a heat range spark plug a possible vacuum leak low compression overly retarded timing or too large a plug gap. If the tip of the plug is any other color or condition it indicates an issue with either the engine the fuel system or the ignition. Normal condition an engine s condition can be judged by the appearance of the spark plug s firing end if the firing end of a spark plug is brown or light gray the condition can be judged to be good and the spark plug is functioning optimally. Most often a light tan color around the tip of the spark plug indicates a healthy and well performing engine. Below we share the spark plug reading chart.

Heat range ground strap the ground strap indicates the heat range of the spark plug. How you crack the ngk code the letter combination 1 4 before the heat rating indicates the thread diameter hexagon spanner width and the design. The easiest vital sign to read is ignition. The 7th letter contains data about special spark plug construction features. If the color of the ground strap changes too close to the ground strap s end which is above the center electrode then the heat range is too cold meaning that the strap is loosing heat too quickly to the base ring and is not able to burn off deposits until near its end.

In general a light tan gray color tells you that the spark plug is operating at optimum temperature and that the engine is in good condition. Looking at the ground strap and the tip of the porcelain insulator you can quickly see the results of knock or timing adjustments before having to dive. If you notice any black dry soot on the spark plug this is a sign of carbon fouling which means your engine has been running too rich and you should visit a mechanic to figure out the cause.