Chevytrucks. org – troubleshooting your gas gauge

Most gas tank units consist of two parts, the gauge mounted in the dash and a tank sender mounted in the tank.

The following trouble-shooting instructions apply to the AC-type fuel gauge, which is one of the most common type of units. Cost of gas heating per month Your service manual will give you any added instructions necessary for your specific type of fuel gauge.


The gas gauge, often located in the instrument cluster, consists of two small coils spaced 90 degrees apart with an armature and a needle placed at the intersection of the two coils. Heat pump vs gas furnace cost calculator A dampener is also located on the armature to prevent excessive needle movement on rough roads.

The tank sender unit is mounted to the outside of the gas tank (with a float on the inside, of course) and is made up of a metal housing that contains a rheostat (which is simply a resistance unit), and a brush that comes in contact with the resistance unit. Gas prices in kona hawaii The opposite end of brush unit is attached to the float arm located inside of the gas tank. Average cost of natural gas per month The movement of the float arm is controlled by the amount of fuel in the gas tank. Route planner including fuel cost The variations in the amount of fuel in the tank cause the arm to move. Cost to install gas furnace and ductwork This changes the resistance of the tank unit, changing the amount of current at the gauge unit coils, which in turn moves the needle located between the coils.

Beginning around 1950, some vehicles have a small voltage regulator behind the dash that supplies a stable voltage supply for the instruments – something less than the battery voltage of six (or 12) volts. Cost of gas per gallon in europe This isolates the instruments from the effects of varying battery and generator voltage. Driving fuel cost calculator So if you are checking voltage at the dash gauges on these cars and you read something less than battery voltage, it may be normal. Average price of gas in united states Follow the power wires from the instruments and you’ll probably find the regulator.

The most common cause of gas gauge trouble is a poor ground, especially at the tank sender unit. Figure out how much gas will cost on a trip It is important that all wiring connections are clean and tight, and free of dirt and corrosion. Estimate fuel cost for road trip uk A poor ground or loose connection to a gas gauge is just as likely to cause problems as loose or dirty battery cables assuredly will with your starting system.

For example, if the gas gauge needle remains on empty when the ignition key is turned to the “on” position and you are sure the gas tank is partially full, battery current may not be reaching the gauge. Cost of gallon of gas 2008 To check further, connect a jumper wire between the ignition switch and the dash gauge. Estimate gas cost for my trip If the gauge now works, replace the defective wiring between the gauge and the ignition switch.

If the gauge needle remains stuck in one place, try turning the ignition switch off and on several times in succession. Costco gas prices marlboro nj This will allow you to determine if it is the dash gauge or the tank sending unit that is defective. How much gas cost for my trip If turning the ignition switch off and on (a half-dozen times is a good test) does not seem to help, and you’ve verified that the dash gauge is receiving power, try the following troubleshooting steps:

A functioning sending unit will have a high resistance when the tank is full and a low resistance when the tank is empty. Cost of furnace gas valve replacement If the gauge reads higher than it should, make sure the wire attached to the electrical terminal on the tank sending unit is making a good ground connection. Average cost of gas per month 2015 If necessary, clean the connection and reinstall the wire to the terminal, then check the gauge operation. How do you calculate fuel cost If that didn’t fix the problem, use a jumper wire to ground the electrical terminal on the tank sending unit to the tank unit housing (leave the wire to the gauge connected to the tank unit). Average fuel price 2013 Turn the ignition switch on. How much in gas will it cost calculator canada If the gauge reads empty or below empty, the sending unit is defective.

If the gauge still reads high, try grounding the tank unit electrical terminal to a clean portion of the frame. How to calculate gas cost If this brings the gauge to empty or below, the tank unit is OK, but there is a bad ground between the gas tank and the body or chassis (or less likely, between the tank unit and the gas tank). Cost gas hours Either way, find and correct the bad connection or merely run a permanent jumper wire from the frame to one of the screws holding the tank sending unit to the tank.

If the gauge still reads incorrectly, the wire from the tank unit to the gauge may be faulty. Gas cost to travel calculations Check by using a jumper wire to ground the tank unit terminal on the gauge (the one not connected to the ignition). Google maps fuel cost calculator mpg If the gauge now reads empty or below, the problem is in the wire leading to the tank (or its connection to the gauge). Costco gas vacaville california If grounding the tank terminal still doesn’t cause the gauge reading to drop to empty or below, the gauge is faulty.

When the gauge reads lower than it should, check at the gauge by disconnecting the wiring from the tank unit. Estimate gas cost for road trip Turn the ignition on and if the needle reads full or above, the gauge unit is probably good and the tank unit or the wiring leading to it are probably the problem. Lap band surgery south africa Reconnect the tank unit wire to the gauge before proceeding.

The next trouble-shooting task begins by disconnecting the wire to the tank sending unit. Petrol fuel cost calculator If the gauge still reads full, there is likely a short to ground somewhere between the sending unit and the gauge. Costco gas station hours san marcos Look for worn insulation allowing the wire to contact the body or frame. Discount tankless gas water heaters If the gauge reads full or above with the wire disconnected, the problem is in the tank unit rather than the wiring. Cost of gas per gallon in canada It could be an electrical fault, or the float may be stuck or may have sunk because of a hole caused by corrosion. How much gas will it cost me Remove the tank sending unit and check it. Fuel calculator road trip uk If the float is bad, you’ll likely hear gas sloshing around in it or see gas dripping out. Gas cost for trip from city to city If the float is OK and the float arm seems to be swinging freely through its full range, replace the tank unit.

Ground the gas tank terminal post of the tank sending unit using a jumper wire. Cost of gastric bypass in uk If the dash gauge now reeds empty, the gas tank unit is defective. Gas prices for road trip If the dash gauge needle fails t move, the dash gauge is defective.

If the gas gauge works, but reads lower than it should, check for defective wiring between the gas gauge and the tank sending unit. Fuel cost calculator road trip australia Also check for a poor ground at dash gauge and the sending unit by using a jumper wire.

If the dash gauge reads empty when the tank is actually half full or greater, the wiring between the dash gauge and the tank sending unit is defective. Cost of gas in germany today Disconnect the wire at the gas tank sending unit terminal. Natural gas price calculator If the gas gauge reads still reads empty, the dash gauge unit is defective.

© 1997 Randy Rundle. Average cost of gas in california All rights reserved. Cheapest petrol in europe Used by permission of the author.

This article was originally published in the March 1997 issue of Classic Auto Restorer (CAR) magazine.

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