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Water in Fuel System

If water enters the fuel system, it can alter the fuel/air ratio and reduce engine power and/or fuel economy, potentially stalling the engine. If water enters the combustion chamber in small amounts, it may be evaporated from the engine heat. If the amount of water is significant, the water can soak the spark plugs and cause an electrical short to the block or making for a weak spark. Enough water can cool the engine to a point where the water cannot boil away. This could cause extended cranking, stalling, or stumbling/very low engine RPM (around 300-500 RPM).

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Poor Fuel Economy

If your vehicle's fuel economy diminishes, water in the fuel system may be the culprit. The water will reduce engine power, but allow the same amount of fuel to be burned. The result being the same fuel burned for reduced mileage.

Engine Stalls

With a small amount of water in the fuel system, the engine may be able to start and maintain itself for a while. However, the combustion will be weaker than normal and may lead to stalling.

Engine Will Not Start

With water in the fuel system, combustion may not occur when attempting to start the engine. The fuel will be diluted to a point where the momentum from combustion cannot sustain the engine motion. The engine may turn over while the ignition is engaged, but the lack of the proper amount of fuel will prevent normal operation.


An engine that is hydrolocked has water inside the combustion chamber that prevents combustion and compression. The engine will be unable to start and possible unable to crank.

See: Hydrolock.


Poor Quality Fuel

Old or mismanaged gas stations can sometimes get too much water condensation inside their fuel reserve tanks, this fuel is then pumped into your vehicle and in some cases will cause a check engine light to come on and perhaps cause misfires and damage to the catalytic converter from too many contaminants in the fuel or too much water.

Condensation in Fuel Tank

Condensation can gather in your fuel tank naturally from the different temperatures and the mixture of fuel and air inside. If the condensation is left unattended it can pool enough water to get inside the fuel system and effect fuel economy. Since water does not burn the engine will have to work harder on watered down fuel, this will rob performance and fuel economy. This can be remedied by pouring a fuel stabilizer or "dry gas" in your fuel tank at every oil change or regular service. This is also recommended in colder climates aswell because if enough water is in the fuel tank it can freeze around the fuel pump and prevent it from starting.

Leaking Fuel Filter

With gas engines, a leaking fuel filter could be a cause for water getting into the fuel system. Although there would be more tell tale signs to look for first, such as fuel leaking from the underbody when the engine is running. This is the only time the fuel pump is leaking. Residual fuel from the fuel lines, and perhaps the fuel tank, can leak out when the vehicle is immobile as well.

If one were to drive through a body of water deep enough and long enough to suck water in through the fuel filter, water could get into the fuel system.

Diesel engines have a much higher pressure exerted on their fuel systems than regular gas engines. This is due to the way diesel engine must introduce fuel into the engines. Since the fuel is under such high pressure, if there is a leak anywhere in the system it will create such a suction on it that will suck more air in than fuel and cause the engine to stall out from starvation or run very poorly. Under the same circumstances, if the air leak is submerged then water could be sucked into the fuel system.

This article was last edited on March 20th, 2011 at 4:31 PM
Category: Fuel System