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June 30, 2005

Keep your fuel tank at least half full

Are you running on empty? A gasoline tank in your car that is less than half full represents a danger to a vital part of your car's fuel system and I do not mean the danger of possibly running out of gas on the road.

The overwhelming majority of cars on the road today are fuel injected; if your car was sold in the Untied States initially within the last 15 years, it is fuel injected. Fuel injection is a very precise way to deliver fuel into the combustion chamber of your car's engine. It is precise because the fuel is delivered at high pressure (in the neighborhood of 35-45 pounds pre square inch) from the gas tank and squirted into the combustion chamber at exactly the right amount at exactly the right time by a computer controlled system in your engine's management system This precision helps to create a very clean burning engine that runs as efficiently as possible (and efficiency equals power).

Before the advent of common fuel injection, cars did not have the advantage of a computer to measure and time the delivery of fuel in the combustion chambers. Relatively crude carburetors were used to deliver fuel and air into the engine for combustion in amounts that were "about right" but hardly as precise as modern fuel injection systems. Carburetors operated on a gravity system of fuel dripping down from the float bowl to the jets that actually delivered the fuel and as a consequence did not require high fuel pressure from the fuel tank. Fuel pressure delivery for a carbureted engine needs to be only about 7-12 psi.

The fuel tank, fuel lines and fuel pump for fuel injected cars needs to be much stouter than a carbureted car because the fuel pressure is so much higher for fuel injected engines. The fuel pump is the largest moving part in the fuel system, pumping gasoline constantly to your engine from the fuel tank, and it is an electrical pump that is working very hard to provide that pressure. Any thing that is electric powered and works hard throws off heat and a build up of heat is the death knell for any kind of electrical component, including an electric fuel pump.

In to keep the electric fuel pump cool, automobile manufactures keep it bathed in a cooling liquid to prevent burn out and premature fuel pump failure. Do they keep it in the radiator? No. Do they keep it in the air conditioning system? No. Most car manufactures put the high pressure, hard working, electrically powered fuel pump in... the gas tank. Your fuel pump is mounted inside your car's gas fuel tank surrounded by gallons of gasoline that help keep the fuel pump cool. Now this may seem counter intuitive to keep an electrical device inside a tank full of volatile gasoline that will eventually be sparked into combustion by an electric spark at the combustion chamber, but this system seems to be relatively safe and we do not hear of cars blowing themselves up on a frequent basis.

But driving your car with less than half a tank of gas on a regular basis, particularly in hot weather is guaranteed to put extra wear on your fuel pump by denying it the cooling that a full tank of gas provides. So keep at least a half a tank of fuel in your tank and protect your fuel pump from early failure.

Posted by Scott at June 30, 2005 7:47 AM


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