Fuel Tank Water Draining

In automotive maintenance, draining water from the fuel tank is a specific procedure carried out under exceptional circumstances (such as driving through floodwaters, pumping contaminated fuel, or after prolonged vehicle storage). As petrol is lighter than water, any water present settles at the bottom of the fuel tank. If the water level rises excessively, the fuel pump will draw it into the fuel supply system, resulting in hard starting, engine judder/misfiring, or even severe mechanical damage.

Why is there water in the fuel tank?

Condensation: In humid climates, significant day-to-night temperature fluctuations cause moisture to condense on the inner walls of the fuel tank. 

Contaminated fuel: Pumping petrol from disreputable petrol kiosks, where underground storage tanks may harbour accumulated water. 

Failed fuel filler seal: An aged fuel filler neck rubber seal or a damaged petrol cap allows rainwater or car wash water to seep inside.

How to drain water from the fuel tank

Quick emergency method (Applicable only to vehicles with a drain plug)

Certain older vehicle models or specific makes feature a drain/discharge plug at the base of the fuel tank.

Steps: Position a catch pan beneath the fuel tank and loosen the drain plug. Because water settles at the bottom, it will discharge first; tighten the plug immediately once petrol begins to flow.

Note: This setup is extremely rare. For safety reasons, the vast majority of modern cars are not equipped with a fuel tank drain plug. 

Suction method (Most common approach)

This is the standard procedure adopted by automotive workshops.

Steps: 

Insert a dedicated, elongated fuel extraction hose through the filler neck right down to the bottom of the tank. 

Use a vacuum extractor or manual siphon pump to draw out the sediment and settled water at the base. 

Inspect the extracted fluid; if separation is evident (petrol floating above water), continue pumping until only clean fuel is drawn. 

Fuel additive treatment (For trace moisture only)

If only negligible traces of moisture are suspected, a Fuel System Water Remover can be utilised. 

How it works: Formulated with hydrophilic agents, this additive emulsifies tiny amounts of water, allowing it to dissolve into the petrol and safely pass into the combustion chamber to be burnt off by the engine.

Suitability: Suitable strictly for minute traces of condensation.

Diagnosis: How to tell if there is water in your fuel tank

Starting issues: Severe engine shaking, jerking, or knocking noises during cold starts, occasionally accompanied by white smoke (water vapour) from the exhaust. 

Loss of power: Hesitation or intermittent power loss while driving, feeling as though the fuel supply is cutting out. 

Inspect the fuel filter: For vehicles with an external inline fuel filter, dismantle it and empty its contents into a clear container to inspect for visible water droplets or liquid separation.

Crucial Safety Precautions

Never work inside an enclosed garage: High concentrations of petrol vapour linger around the fuel tank, where even a tiny electrostatic spark can trigger a disastrous explosion. Always carry out this job in a well-ventilated open area, handled by qualified mechanics using anti-spark, explosion-proof tools.

Beware of fuel pump failure: Excess water will quickly ruin the fuel pump due to internal corrosion and loss of lubrication. If substantial water contamination is confirmed, a complete fuel flush and tank cleaning is strongly advised over simple draining. 

Do not crank the engine: If you realise that heavily contaminated fuel has been pumped into the tank, do not attempt to start the engine. Once water enters the fuel injectors and high-pressure fuel pump, repair bills will escalate drastically.

Preventive Tips 

Refuelling choices: Stick to major, reputable petrol stations. 

Avoid running on empty: Keeping the fuel tank near empty allows more ambient air inside, which accelerates condensation buildup. 

Inspect seals periodically: Check the rubber gasket on the petrol cap regularly to ensure no rainwater can seep past the seal.