What is Engine Detonation?

Engine detonation refers to spontaneous combustion of the remaining fuel/air mixture in the chamber after normal spark-initiated combustion.

July 21, 2021

The terms “pre-ignition” and “engine detonation” are often thrown around interchangeably to describe the phenomenon that causes engine knock. While pre-ignition refers to early ignition of the fuel/air mixture prior to the spark plug firing, what is engine detonation? Another abnormal combustion event, engine detonation refers to spontaneous combustion of the remaining fuel/air mixture in the chamber after normal combustion is initiated by the spark plug.

In a properly running engine, spark-triggered ignition typically occurs a few degrees before the piston reaches top dead center (TDC). This careful timing ensures the downward force of the exploding fuel/air mixture works in tandem with downward piston momentum, resulting in optimum efficiency and power.

Engine detonation, however, can be caused by excess heat and pressure, leading to engine knock. Computers in modern vehicles can detect engine knock and compensate by adjusting engine timing. While this saves your engine from destroying itself, performance and fuel economy can suffer.

Causes of engine detonation

While a myriad of factors can cause engine detonation and knock, these are three of the most common.

Excess carbon can cause engine detonation.

1) Carbon deposits

Carbon deposits in the combustion chamber can be damaging if they get hot enough to ignite any residual fuel from the combustion event or if they clog injectors and impact spray patterns, leading to excessive residual fuel.

While all gasoline sold in the U.S. must be formulated with a lowest additive concentration (LAC) level of detergent additives, it takes a very low level of additive to pass the tests. The low levels of detergent additives in modern gasoline allow deposits to build up on critical fuel system components.

Clean deposits with AMSOIL fuel additives


AMSOIL P.i. Performance Improver is an effective one-tank, total fuel system cleaner. More potent than other fuel additives on the market, P.i. effectively cleans everything the fuel touches, including both port and direct fuel injectors, intake valves and combustion chambers, in only one single tank of gasoline.

AMSOIL Upper Cylinder Lubricant

AMSOIL Upper Cylinder Lubricant contains detergent additives designed to maintain injector cleanliness. While AMSOIL P.i. is designed to attack and remove stubborn injector deposits that can reduce power and fuel economy, Upper Cylinder Lubricant helps preserve injector and combustion-chamber cleanliness. Using it with every tank of fuel helps retain fuel-economy and performance gains and maximizes component life.

Excessive heat can cause engine detonation.

2) Coolant/cooling system

An overheating engine is more likely to experience the effects of engine detonation. Check your coolant level. If it’s low, top it off. If that doesn’t work, inspect your cooling system to make sure everything is in working order. Keep an eye out for a bad water pump, missing fan shroud, a thermostat that’s too hot or slipping fan clutch.

Ensure outstanding cooling-system protection with AMSOIL coolants

AMSOIL Passenger Car/Light Truck Antifreeze & Coolant and Propylene Glycol Antifreeze & Coolant provide superior heat transfer and excellent protection against corrosion, freezing and boil-over. They provide maximum protection in extreme temperatures and operating conditions.

Spark plug

3) Incorrect spark plugs

In addition to producing spark, spark plugs withdraw heat from the combustion chamber and into the head. They are designed to operate within a certain heat range, and using spark plugs different from OEM recommendations can lead to engine knock.

Make sure you’re using the correct spark plugs to help avoid detonation.

More like this