A flooded engine is an
internal combustion engine
An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
that has been fed an excessively rich air-fuel mixture that cannot be ignited. This is caused by the mixture exceeding the
upper explosive limit for the particular fuel. An engine in this condition will not start until the excessively rich mixture has been cleared.
It is also possible for an engine to stall from a running state due to this condition.
Engine flooding was a common problem with
carbureted
A carburetor (also spelled carburettor) is a device used by an internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the venturi tube in the main meteri ...
cars, but newer
fuel-injected
Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines.
All com ...
ones are immune to the problem when operating within normal tolerances. Flooding usually occurs during starting, especially under cold conditions or because the
accelerator has been pumped. It can also occur during hot starting; high temperatures may cause fuel in the carburetor float chamber to evaporate into the inlet manifold, causing the air/fuel mixture to exceed the upper explosive limit. High temperature fuel may also result in a
vapor lock
Vapor lock is a problem caused by liquid fuel changing state to gas while still in the fuel delivery system of gasoline-fueled internal combustion engines. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carbur ...
, which is unrelated to flooding but has a similar symptom.
A severe form of engine flooding occurs when excessive liquid fuel enters the combustion chamber. This reduces the dead volume of the combustion chamber and thus places a heavy load on the
starter motor
A starter (also self-starter, cranking motor, or starter motor) is a device used to rotate (crank) an internal-combustion engine so as to initiate the engine's operation under its own power. Starters can be electric motor, electric, pneumatic ...
, such that it fails to turn the engine. Damage (due to excessive compression and even dilution of the lubricating oil with fuel) can also occur. This condition is known as the engine "flooding out." Possible causes of too much liquid fuel in the engine include a defective carburetor float that is not closing the fuel inlet needle valve, or debris caught in the needle valve preventing it from sealing.
Liquids inside an internal combustion engine are extremely detrimental because of the low compressibility of liquids. Although not the most common cause, a severely flooded engine could result in a
hydrolock
Hydrolock (a shorthand notation for hydrostatic lock or hydraulic lock) is an abnormal condition of any device which is designed to compress a gas by mechanically restraining it; most commonly the reciprocating internal combustion engine, the ...
. A hydrolock occurs when a liquid fills a combustion chamber to the point that it is impossible to turn the crankshaft without a catastrophic failure of the engine or one of its vital components.
The conventional remedy for a flooded carbureted engine is to steadily hold the throttle full open (full power position) while continuing to crank the engine. This permits the maximum flow of air through the engine, flushing the overly rich fuel mixture out of the exhaust. If the exhaust system is hot enough to
autoignite, an after-fire may result; this can be seen as a flame discharging through the exhaust system. On a fuel-injected engine, ignoring the throttle (no fuel) while starting permits electronic logic systems to produce the correct fuel mixture, often based on exhaust gases. Some fuel injection computers interpret "pumping" the throttle to indicate a flooded engine, and alter the fuel-air mixture accordingly. In a carbureted engine equipped with an accelerator pump (which advances fuel flow to match air ingestion under rapid throttle acceleration), "pumping" the throttle will force excess fuel into the engine, further flooding it.
In worst cases, the excess fuel can foul
spark plug
A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...
s, sometimes necessitating their cleaning or replacement before the engine will start. This is most likely to occur on a carbureted engine in cold weather, after a running engine has been shut off briefly before being restarted. Doing so can cause the
choke valve
In internal combustion engines with carburetors, a choke valve or choke modifies the air pressure in the intake manifold, thereby altering the air–fuel ratio entering the engine. Choke valves are generally used in naturally aspirated engines t ...
to configure the mixture for a cold engine start, despite higher actual temperatures, resulting in an overly rich mixture and flooded engine.
See also
*
Vapor lock
Vapor lock is a problem caused by liquid fuel changing state to gas while still in the fuel delivery system of gasoline-fueled internal combustion engines. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carbur ...
References
{{Reflist
Engine problems