When you fire up your motor day after day, year after year, you might never give a thought to these small marvels of precision engineering. Until, of course, they start to fail and you notice issues. It's pretty impressive, however, that spark plugs can fire flawlessly for thousands of miles in such a harsh and volatile environment.
What It Does
The spark plug emits precisely-timed arcs of electrical energy (voltage) to ignite the atomized air/fuel mixture in the combustion chamber, literally, "firing up" your engine. After your motor is running, it continues to fire through each combustion cycle. The spark plug also pulls excess heat from the combustion chamber and transfers it to the cooling system.
What is the "Heat Range?"
You may have heard the descriptions "cold" and "hot" spark plugs. Though these terms sound like descriptions of temperature, this is incorrect. These terms refer to the time the plug takes to pull heat from the firing tip to the cylinder head and into the cooling system. The length and thickness of the insulator nose controls how fast the spark plug can transfer the heat.
Spark plug manufacturers assign numbers to indicate the heat range of the spark plug. A plug with a shorter insulator nose (draws heat faster) is described as a "cold plug" and, conversely, those with a longer insulator nose (draws heat slower) is referred to as a "hot plug."
What Type of Spark Plug Do I Need?
The central electrode of a spark plug is constructed with copper, nickel, chromium, platinum, or iridium. The type of metal determines conductivity, lifespan, and cost.
Talk to a service advisor at I-86 Truck & Auto Repair or consult your owner's manual for guidance when choosing replacement plugs. A key decision is whether to replace with the kind recommended by your manufacturer, or step up to a rare-metal variety.
Signs That Spark Plugs May Need to be Replaced
- Trouble starting engine
- Pinging or knocking noises
- Misfiring
- Rough idling
- Decrease in fuel economy
- Difficulty accelerating
What Is Spark Plug Fouling?
When the firing tip (insulator nose) of the plug becomes covered with oil, carbon, or fuel residue, the voltage can fail to bridge the gap and ground out. Under ordinary conditions, spark plugs can burn off residue and keep firing properly for thousands of miles.
Possible Causes of Spark Plug Fouling
- Air-fuel ratio that is too rich
- Malfunctioning fuel injection
- Worn piston rings
- Worn valve seals
What is Gapping?
The "gap" on a spark plug is the space between the conducting electrode and the plug tip. If the gap is too short, the spark may not be strong enough to fire. A gap that is too long can cause misfiring. When replacing plugs, set the gap to your auto's specs with a feeler gauge.