Why is My Fuel Gauge Not Accurate

Why is My Fuel Gauge Not Accurate

As motorists we depend on the information from our fuel gauge to help us decide when it’s time to get off the interstate and fill up. I’ve owned cars you could drive around on empty for a week with no problem and others that would run out of gas somewhere between a quarter tank and empty. Learning the quirks of your particular fuel gauge and its accuracy is an important part of the bonding relationship between a driver and car. This article will discuss the variables involved in fuel gauge accuracy and some real-life examples of how you can figure out just how far you can drive when the gas gauge reads empty.

Fuel Level Gauge

Obviously, this is the device on the dash board that provides feedback to the driver of how much gas remains in the tank. Manufacturers have been known to use two distinctive types. An analog meter is the kind with a pointer usually set against a black and white background with measurements of empty, quarter, half, three-quarter and full.

The analog gauge converts an electronic signal from the tank to correctly point at the right area on the background.Some car makers will use a digital version of the fuel level gauge. This is usually a stack of bars that fills a field mounted next to a background with empty at the bottom and full indicating the tank is near maximum capacity. Digital gauges also receive their information from the fuel tank, but often pass it through a buffer so individual bars do not flash on and off under certain conditions. Dealerships have special variable resistance tools to test gauge accuracy for their specific models.

Fuel Tank Sending Unit

On modern automobiles, you often find a fuel sender is part of a combination package known as a fuel pump module. On GM cars this is a round plastic housing that fits down into the center of the fuel tank. It contains the pump, fuel inlet nylon filter, molded fuel lines and the fuel tank sending unit. Overall, the design of the sender hasn’t changed much in the last fifty years.The fuel tank sending unit contains a variable resistor control by an arm that is attached to a float. When the fuel level is low the float hangs down changing the resistance so the gauge needle or number of lit bars indicates a low fuel level. In the inverse when the tank is full, the resistance in the sender is high and movement of the gauge indicator points to show an appropriate level.

Running on a Low Fuel Tank

When first getting to know an automobile and determining how far you can go as the needle approaches empty, one vital piece of information must be obtained. You need to know how many gallons the tank holds. This is indicated in the vehicle’s owner’s manual. As the gauge approaches empty, head to the gas station and record how many gallons of gas it took.Subtract the number of gallons installed from the one obtained in the owner’s manual. The number should be small and can be multiplied against average miles per gallon to determine exactly how much further you could’ve gone before physically running out. As a real-world example, if you have a 20 gallon tank and pump fifteen when it was on E that left you with 5 gallons remaining. If that automobile averages 20 miles per gallon, you could’ve actually driven another hundred miles before it ran dry.

Things to Think About

Some people would say that the above example is not valid because a car cannot run to the 0 gallon point. Although this is true, some manufacturers put in a 1 to 5 gallon emergency reserve. This is In addition to the advertised total gallons indicated in the owner’s manual. They do this to provide the driver and car maker a little wiggle room when it comes to the word empty.Another thing to consider is that running out of gas is generally not recommended by professional mechanics. This is because the dirtiest part of the fuel tank is at the bottom.

Although there is a protective nylon sock filter at the inlet in addition to the regular line fuel filter, it’s still possible to suck up the worst stuff when the tank is run very low. Another downside to running a vehicle out of fuel is it can cause premature fuel pump failure. This is because gas is a petroleum product and is actually used to lubricate the impeller inside. Running any rubber impeller type pump in a dry state is not good for it.

I know people that are more than curious about how far they can drive their particular vehicle on empty. They want to know where the fuel gauge points when the pump has sucked up its last available drop. In order to accomplish this, they carry an extra approved gas container in their trunk and set out to drive the vehicle until it stalls. After its run dry they install the 5 gallons from the trunk and cycle the ignition key to work gas up to the injector rail so the engine restarts quickly. When I review all of the reasons why they shouldn’t do this, the response is “inquiring minds want to know”.

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