Fuel tank clean out procedure.

Since the first fuel tank was introduced there has been the risk of condensation depositing a volume of water in the fuel over time. That still exists today but in reality the volume is minute and the time frame required is generally long. This happens when the contents of the tank goes through the normal heating and cooling cycle of a typical day; in the heat of the day fuel expands pushing air out of the tank. In the evening the fuel cools and contracts pulling cooler and moist air into the tank. Cooling causes condensation of the moisture and the condensation clings to the walls of the tank. The resulting water settles and accumulates at the bottom of the tank being heavier than gasoline. This relatively minor amount of water could be effectively removed with a typical water separating fuel filter, or even harmlessly removed with one of many fuel additives. With ethanol in the mix though those days are gone.

Fuel tanks still go through the breathing process and there is still the same level of condensation but the water doesn't settle to the bottom anymore. Water readily mixes with ethanol, therefore the water is suspended in the fuel, much the same way it used to be suspended with fuel additives. In fact, most fuel additives for straight gasoline are mostly ethanol. The differences is in quantity. We never put as much as ten percent fuel additive in a tank of gasoline so the fuel has much more ability to absorb water than treated gasoline. In addition to the condensation of water ethanol has the ability to absorb moisture directly from the air bypassing the condensation step. This absorption dramatically speeds up the water accumulation process shortening the shelf life of stored fuel to only a few months, or even weeks before a phenomenon called phase separation takes place.

In phase separation the ethanol reaches its water absorption limit where it becomes too heavy to remain suspended in the gasoline, and it simply falls to the bottom of the tank as a water/ethanol mix. The bottom of the tank is where the fuel pick up line is of course, so the next time the engine is run it will be picked up and fed into the engine where the engine will fail to continue running. If no harm is done initially but the water/ethanol mix is left in the engine's fuel system long enough without being flushed, irreversible and/or expensive engine repairs can be needed. If the water/ethanol mix remains in the tank long enough another new problem can develop. As odd as it sounds organic growth can now begin in the fuel tank. If you think about it that's not as odd as it at first sounds. Ethanol is an organic compound, and it's mixed with the source of all life; water. Mold and fungus now have a fertile bed to grow and this stuff can clog the best fuel filter in short order, not to mention the havoc it can cause if it gets into a fuel injection system on the engine.

I've spoke with many individuals with water in the fuel issues through the years but with the instroduction of ethanol in our fuel this problem has increased dramatically. Most people suspect a leaking fuel tank as the cause, or possibly a leaking fuel cap or lines. This can be the cause and should be investigated but it's really not likely. The quantity of suspected water in the tank is usually in the gallons. Think about how long it would take for a gallon of fuel to get into a tank from rain even if the fill cap were left off. A hole in the tank also most often results in a fuel leak instead of water intrusion. The only spot on a tank that occasionally allows a considerable volume of water intrusion is the gasket under the fuel level sending unit on top of the tank.

Curing the problem takes some work but most people can do it themselves. The key is to remove all of the fuel from the system; all being the key word. If only a minor amount is left it can be enough to foul the filter and injectors or carbs again so everything has to be removed from the tank and the tank should be dried out. This can't be accomplished by simply using the fuel supply pick up and hose attached to the tank. You need to go in through the fuel sender hole by removing the sender and angling the tank so that all the fuel can be siphoned from the tank, then the tank should be allowed to dry completely. Angling the tank can be accomplished easily if it is on a trailer by raising the front of the trailer causing the contents to flow to the rear, then you may need to raise one wheel at a time to be sure nothing is trapped behind a baffle. All of the fuel should be properly disposed of. Do not try to separate the gasoline from the water/ethanol mix. Because the ethanol is part of the octane of the gasoline the remaining pure gasoline is not safe to use without risking serious internal engine damage which can result from pre-ignition and detonation. Once the tank is completely clean and dry refill with fresh gasoline, then flush all the lines and install a new filter. Be sure to flush all the lines on the engine as well.

Another common scenario is when the tank is pumped, filled with fresh fuel and flushed, and everything is fine, but comes right back in just a few weeks. This is when most are convinced there is a leak allowing water into the tank, and it can be, but again ethanol may be the explanation. If the tank was pumped but part of the water/ethanol mix was missed, and then fresh fuel is pumped on top of that, you now have enough ethanol in the fresh fuel to suspend the water that is left in the tank, but it is near saturation level where phase separation can again occur. Under these circumstances the time frame it takes for the problem to return is dramatically shortened. If it comes right back, you most likely didn't get it all.

Why is there so much of this mixture? It's got to be a leak to get this much; right?

Remember, ethanol laced gasoline is around a 10/90 % mixture. If your tank holds 20 gallons of fuel for instance, it can contain 2 gallons of ethanol. When the ethanol absorbs enough water and separates out of the fuel in this tank the resulting sediment would exceed two gallons which will appear to be a huge quantity of water. This is a possible logical explanation for the huge quantities I'm hearing of in the fuel tanks.