An aircraft operated primarily at low cruise power settings is experiencing persistent spark plug fouling. Assuming mixture leaning procedures are already correct, which spark plug characteristic should the technician review to help prevent this fouling?
- AInstall spark plugs with a hotter heat range to help keep the firing tip hot enough to burn off deposits
- BIncrease the spark plug reach to place the electrode deeper into the combustion chamber
- CDecrease the spark plug gap to increase spark intensity
- DInstall spark plugs with a colder heat range to keep the firing tip cooler
Show answer & explanationAnswer & explanation
Correct answer: A. Install spark plugs with a hotter heat range to help keep the firing tip hot enough to burn off deposits
Spark plug heat range describes how quickly the plug transfers heat away from the firing tip; a colder plug promotes fouling at low power because the tip stays too cool to burn off carbon/lead deposits, while a hotter plug (within the manufacturer's approved range) retains more heat and helps prevent fouling. Reach and gap are physical dimensions unrelated to heat dissipation and would not directly resolve fouling caused by low operating temperatures.
Why the other options are wrong
- B. Reach refers to thread length into the cylinder, not thermal characteristics.
- C. Gap affects spark energy required, not the plug's thermal fouling tendency.
- D. A colder plug would worsen fouling by keeping the tip even cooler.
Spark Plug Heat Range
A rating describing how rapidly a spark plug transfers heat from its firing tip to the cylinder head; selected based on typical engine operating conditions.
- Cold plugs dissipate heat quickly, resist preignition, but foul easily at low power
- Hot plugs retain heat, resist fouling, but risk preignition at high power
- Manufacturer specifies approved heat range for each engine
- Improper heat range can cause fouling or detonation/preignition
Memory trick: Cold plug = clogs; hot plug = clears