What do bad spark plugs look like?
Rough idling, misfires, and poor performance are just a few signs that your spark plugs need attention. Bad spark plugs can make your car frustrating to drive, and if left unattended for long periods of time, they can lead to engine damage.
Read on to find out the most common symptoms of worn or defective spark plugs. We’ll also tell you about the normal lifespan of spark plugs and the average replacement cost so you can plan your budget accordingly.
What does a good spark plug look like?
A light gray, yellow, or brown discoloration of the ceramic insulator around the center electrode, combined with a clean side electrode, indicates normal combustion. This indicates that an optimal fuel-air mixture is burning properly in the cylinder.
Light deposits on the tip of the insulator indicate some oil consumption, but as long as the spark plug is firing properly, this is nothing to be concerned about.
Soot/Carbon Contamination
This condition of the spark plug indicates that the engine is running too rich. h. Too much fuel. Possible causes include a dirty air filter, mixture control not working properly when cold or during long or short distance runs, and incorrect spark plug heat range.
Oil Contamination
This oil contamination condition indicates that excess oil is getting into the combustion chamber during operation. Possible causes include overfilling the crankcase, poor crankcase ventilation, and oil leaks due to worn piston rings or valve stem seals.
Lead Contamination
Spark plugs have a yellow-brown glassy deposit that coats their inner surface. A greenish tint of the underlying material may also be visible. This glaze appears baked on and varies from a thin layer to a completely covered layer that has partially flaked off.
Ash deposits
The spark plug appears to be covered in a thick, cream-colored, ceramic-textured compound. This ash deposit is so brittle that it can be scraped off with your fingernail or a pocket knife blade.
Center or side electrodes eroded/dissolved
The spark plug center electrode and/or side electrode show significant material loss. The electrode may appear eroded, rounded, or melted. The ceramic insulator tip may also be bubbling, soft, or cracked.
This type of thermal damage occurs when the spark plug overheats due to extreme combustion temperatures. Common causes include low octane, excessive ignition timing, pre-ignition, lean air-fuel ratio, or inaccurate spark plug heat readings.
Severely worn center electrode
Inspection reveals that the spark plug center electrode has significant erosion and, in severe cases, significant or complete wear of material. This severe electrode wear indicates that the spark plug has exceeded its useful life.
Excessive side electrode wear
When inspected, the spark plug side electrode shows significant metal wear and erosion. In advanced cases, nearly all of the electrode material has evaporated.
This accelerated side wear is usually caused by damage from an explosion in the cylinder. The main causes include low octane, pre-ignition, or excessive oil/fuel additive consumption.
Broken Center Electrode Insulator Tip
Upon visual inspection, a portion of the tip of the ceramic insulator around the center electrode appears to be chipped or broken off. This results in a gap or missing section in the insulator tip.