When condensation from water contaminates a gas tank, the most common symptoms are poor fuel economy, engine running rough, stalling or failing to start, and hydrostatic lock. Condensation inside a fuel tank or a leaky fuel filter can contaminate gas that has been stored too long.
Water in the gas line reduces engine power, fuel economy and decreases engine efficiency while using the same amount of fuel. Water in the gas line can prevent combustion from occurring when attempting to start the engine. The fuel will be diluted to a point that momentum from combustion cannot sustain the engine motion. The engine may turn over, but the operation will not be efficient.
In some instances when the engine is engaged, a loss of fuel efficacy to condensation may prevent continued operation. Even a small amount of water in the gas line will weaken the gas and create engine knocking or stalling.
When gas contaminated by water enters the engine's combustion chamber, it can prevent combustion and compression. As a result, the engine will not start and may not even be able to turn over. This phenomenon is called hydrostatic lock.
Finally, even without apparent mechanical symptoms, water in the gas line can cause the car's engine light to come on.