TextA spark plug failure can be a result of many different things. This blog post will contain five possible reasons on why your spark plug is failing. These reasons include: carbon fouling, oil fouling, overheating, pre-ignition, and insulator breakage. Visual and written descriptions will be provided for each possible reason.
Reason for spark plug failure?
Normal Condition
Before outlining what spark plugs look when they’re failing, let’s start by looking at what a normal spark plug should look like.
Appearance:
- The base of insulator becomes white or gray when using unleaded gasoline
- Electrode may become burned
- The base of insulator becomes light brown when using leaded gasoline
Carbon Fouling
Appearance:
- Dried carbon deposited covering insulation base as well as electrode area
Engine:
- Faulty engine stability at low speeds
- Engine may die often
- NOTE: nearly 90% of engine problems are a result from carbon fouling or oil fouling on forklift spark plugs
Causes:
- Incorrect thermal value
- Idling of the engine for too long / driving in cold temperatures
- Rich air-fuel mixture
- Clogged air filter
- Delay in ignition timing
Fixes:
- Causes 1 or 2: use spark plug with a thermal value that is one level lower OR adjust engine idling.
- Causes 3-5: perform complete readjustment and tune-up
Oil Fouling
Appearance:
- Base of insulator and electrode becomes shiny black; covered with oil or gasoline
Engine:
- Faulty engine stability at low speeds
- Engine may die often
- NOTE: nearly 90% of engine problems are a result from carbon fouling or oil fouling on forklift spark plugs
Causes:
- Leakage of oil into combustion chamber from frictional wear of piston rings, valve guides, or cylinder wall.
- Rich air-fuel mixture
Fixes:
- For cause 1: if forklift spark plugs become wet, simply clean the plug and reinstall it. If not, the engine requires a complete overhaul.
- For cause 2: adjust the carburetor.
Overheating:
Appearance:
- Base of the insulator will be burned and will appear bleach white from the heat
- Electrode will be burned and become white / dark purple
Engine:
- Engine horsepower decreases and speed falls when running at high speeds continuously as well as: driving for a long time uphill, or pulling too great a load
Causes:
- Incorrect thermal value of plug
- Use of low octane gasoline
- Ignition timing set too early
- Inappropriate cooling
- Poor air-fuel mixture
Fixes:
- Cause 1: use a spark plug with a higher thermal value
- Cause 2: use higher octane gasoline
- Cause 3: adjust ignition timing
- Cause 4: check the cooling system
- Cause 5: adjust the carburetor
Pre-ignition:
Appearance:
- Electrode will be melted
- Base of insulator is also melted, in extreme cases
Engine:
- Caused by overheating
- Temperatures in combustion chamber increase rapidly – destroying the spark plug as well as the piston head
Causes:
- Incorrect thermal value of plug
- Use of low octane gasoline
- Ignition timing set too early
- Inappropriate cooling
- Poor air-fuel mixture
Fixes:
- Cause 1: use a spark plug with a higher thermal value
- Cause 2: use higher octane gasoline
- Cause 3: adjust ignition timing
- Cause 4: check the cooling system
- Cause 5: adjust the carburetor
Insulator Breakage:
Appearance:
- Base of insulator has vertical crack
- Appearance is similar to problems with overheating or lead fouling
Engine:
- Engine horsepower decreases and speed falls when running at high speeds continuously as well as: driving for a long time uphill, or pulling too great a load
Causes:
- Incorrect thermal value of plug
- Ignition timing set too early
- Inappropriate cooling
- Poor air-fuel mixture
Fixes:
- Cause 1: use a spark plug with a higher thermal value
- Cause 2: adjust the ignition timing
- Cause 3: check the cooling system
- Cause 4: adjust the carburetor
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Need More Help?
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