Draining a Diesel Engine's Water Separators
Diesel fuel can easily become contaminated by water because diesel fuel absorbs water more than gasoline does. For this reason, many diesel vehicles feature a gadget called a water separator that collects water from the fuel. It’s usually located on or near the fuel filter. If your vehicle doesn’t have one, you can have one installed. The part shouldn’t be terribly expensive, and it can save you a bunch of money on repairs.
Although a few water separators are self-cleaning, most need to be manually drained: You just turn a little drain valve called a petcock and empty the water from the collection chamber of the separator.
It’s a good idea to check the water separator weekly at first to see how fast it fills up under normal conditions when you’re driving on fuel from your usual source. If the fuel contains a lot of water, you may want to consider buying fuel elsewhere.