You are here

Gauge Engine Health by Spark Plug Condition

The color and condition of a spark plug can reveal much about what is going on inside your engine. For example, a plug coming from a properly operating engine is grayish-tan to white. Don’t be alarmed if the plug is pinkish-red because this comes from using additives in unleaded fuel. Appearances that warn of engine problems include:

  • An insulator tinted charcoal with a firing tip that is damp with gas indicates a faulty choke, overly rich fuel mixture, ignition problems, leaking fuel injectors, or too low a plug heat range.
  • A firing tip covered with black soot can indicate too cold a plug heat range, an improperly adjusted carburetor, or malfunctioning choke.
  • When the ceramic tip, center, and electrodes are coated with a black, oily substance, then oil is entering the combustion chamber, indicating worn rings, valve guides, or valve seals (shown at right).
  • A cracked, chipped, or broken insulator is caused by low-octane fuel or over advanced timing.
  • Electrodes that are eroded, have rounded edges, and are excessively worn away should be replaced.

Tips to tightening spark plugs

There is definitely a trick to properly tightening spark plugs. Autolite offers this guide to follow in the absence of a torque wrench.

  • For 14-mm and 18-mm spark plugs with tapered seats, tighten the plug 1⁄16 turn beyond finger tight.
  • Turn 14-mm and 18-mm gasket seat plugs 1⁄2 turn past finger tight.
  • Turn 12-mm gasket seat plugs 3⁄8 turn past finger tight.
  • Turn 10-mm gasket seat plugs 1⁄4 turn past finger tight.

Always install spark plugs with clean and dry threads to avoid stretching or overtorquing the plugs, which can result in engine damage.

Read more about

Machinery Talk

Most Recent Poll

Will your planting schedule be delayed?