Engine Maintenance

What Causes Engine Knocking


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Engine knocking, or pinging, is a term often used to describe an irregular sound made by a vehicle engine when there is a problem with the handling of air/fuel mixture within the cylinders. Normally, this sound is heard when the vehicle is idling and it can be either weak or strong. A strong knock generally indicates a problem which should be addressed to prevent irreversible damage to the engine.

Causes of Engine Knocking

Engine knocking is directly caused by a small explosion that occurs outside of the normal timeframe for spark plugs vs. pistons. There are a number of abnormalities that can lead to off-timing for this process, causing the engine to knock or ping. Some of these abnormalities are inconsequential and others can lead to a complete seizure of the motor over time. Following is a list of potential causes for an engine knocking sound:

  • Improperly mixed fuel (ie: water in the gas)
  • Timing off
  • Irregular cylinder pressure
  • Sharp edges on pistons or valves (due to wear and tear)
  • Low coolant level
  • Cooling system problems
  • Overheating
  • Improper spark plugs
  • Overheating exhaust valve, due to poor seating or weak valve spring
  • Slipping fan clutch

Diagnosing the Cause

It's important to properly diagnose the cause of an engine knocking noise, due to the potential damage that may occur over time. If you are mechanically inclined, you may be able to inspect the motor to determine the cause of the pinging, or at least assess the situation by ruling out one or more potential problem areas. If not, it's important to have a mechanic assess the situation immediately. If you suspect poor gas, you may purchase a fuel additive to see if that alleviates the knocking sound, or run the vehicle through the current tank of gas, and refill with higher-grade octane gas to rule out other problems. Since a number of scenarios can lead to an engine knocking sound, it's important to determine the cause as accurately as possible. 

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