How To Drain Your Civic’s Gas Tank

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There are some occasions when the fuel tank of your Honda Civic needs to get drained, besides burning the fuel in your engine while annoying your neighbors.

One of these came up to me recently, when I found out that the two year old fuel inside the tank of our current project car, was very unimpressed of the tiny sparks produced by the spark plugs. There was no chance to fire the engine up, and the combustion chambers got filled up with old, bad fuel.

It was apparent that we had to find a way to remove the old fuel from the tank.

#1 Drain Plug

The first thing which came to my mind was a drain plug - like these being used for draining the engine and transmission oil.

If your Civic belongs to the older generations, you'll find such a drain plug at the bottom of the gas tank, usually on the driver's side. All you have to do is grab a big enough bucket or gas can, placing it under the drain plug, and unscrew it.

To speed this process up, open the fuel cap. This ensures that there's no vacuum built up inside the tank while the fuel is draining.

1992 Civic EG3 Fuel Tank Drain Plug
Drain plug of a '92 Civic EG

#2 Fuel Pump

I spent a decent amount of time finding the drain plug on my '03 Civic EM2. There was none.

What's the usual way the fuel gets into the engine? It gets pumped out! So, why not use the power of the fuel pump? Since our tank was only 1/4 full, it was a possible option.

The first step is removing the fuel hose from the fuel rail on your engine. Before, release the pressure inside the tank by opening the fuel cap.

Keep an old cloth handy while pulling off the hose and wear some eye protection. It's possible that there's still enough pressure on the line to ruin your meticulously cleaned engine bay. Now you can put the open end of the hose in a gas can.

Now we are ready to turn on the pump.

To let the fuel pump do its job, you have to turn the ignition key to the second position (II). This works for exactly two seconds until the fuel pump relay decides to interrupt our plan. It shuts off the pump after the fuel pressure was built up.

The fuel pump relay (blue) is located behind the glove box.

Since we cannot fire up our engine, we need to find a way to let the pump run continuously while the ignition key is in the second position.

When the motor is running, the fuel pump relay receives battery voltage (12V) on one of the four connected wires. Simplified, this "activates" the relay and the fuel pump receives power. Another connected wire provides the relay with battery voltage continuously, as long as ignition is on.

To let the pump run longer than only two seconds, we put battery voltage on the relay wire, which is connected to the fuel pump.

Simply bridge the two wires.

If you turn on the ignition now, the pump will receive battery voltage continuously and won't get shut off after two seconds. First, make sure that the fuel hose is disconnected and placed into a gas can.

After we'd set everything up, the old fuel got soaked out of the gas tank automatically and we were able to fill in some fresh fuel.

Finally, the engine was screaming 🙂

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