The Stovebolt Site Forums The Shop Area The Electrical Bay Fuel gauge dilema

My original (12 volt converted) gauges show 1/2 full with a full tank. Is it my sending unit that needs to be replaced? I have an aluminum, side rail mounted tank, with an aftermarket sender, on my '48 AD pickup. Thanks for any help with determining the correct sending unit for my gauge.

Hy wes thomas, the sending unit and gauge must be matched as far as their resistance is concerned in order to work correctly together. There are at least six different resistances currently in use in the industry, we can't even get the engineers to agree on what resistance value to use! Good grounds at the fuel tank to frame connection, and at the gauge to dash connection are also a must, hope that helps.

If you have a 90 ohm gauge with the original 30 ohm sending unit you'll never get it to show full without putting a 90 ohm sending unit in the tank. You really don't need to change anything if you remember that 1/4 on your gauge really means you have a half tank of gas if your gauge reads half when full.

Hello Wes Thomas, Welcome to Stovebolt.com

To test if the sending unit is working there should be 5 or 6 screws on the top of the sending unit. Unhook the battery to guard against sparks. Pull up on the sending unit and look at the position to see if it is floating on the gasoline or is it installed sideways where the float is rubbing on the side of the tank. If so, then turn it to a place where it will move with out the float hitting the tank and the screws line up, adjust as described below. If not continue the test this way; Remove the sending unit. Move the sending unit as far away from the gas tank and stuff a rag into the SU hole to stop the gas fumes from making their way towards the place you are working. Get it as far away as the sending unit wire will let you. Use a jumper and hook the sending unit up to ground on the edge of the medal top, you can put a screw and nut through a hole to do this temporally to get a ground. Turn the key on. Slowly move the arm up and the gauge should start to move towards full, move the float arm down and it should move towards empty. If the aluminum tank you have is flatter and spans the frame the float moves up and down a lot less. The way to adjust a aftermarket sending unit is to bend the float arm to match as closely as possible to the gas height. When the gas is low or empty the float should be in the down position to show empty. When full the inverse happens the float should be to the top to show full. If moving the arm doesn't change the gauge on the dash you can use a voltage gauge to see if the voltage changes as you move the arm. This part is speculation from me, the 6 to 12 volt conversation may need a voltage step down to keep the gauges 6 volt. If the gauge goes all the way from full to empty with the sending unit out of the tank the problem is the arm adjustment as described above and not the voltage. Good Luck. John

an original gauge requires a 30 ohm sender, aftermarket universal type senders come in various ratings from 30 ohms to 250 ohms as 3B says, if you have the correct 30 ohm sender, it likely just needs to be adjusted properly to fit the non-original tank you have - here's some info and pictures on setting it up

Bill

Thank you so much for the great info. I will have the ohmage(sp) checked, and adjust accordingly.

Wes

Easy to check if you have a simple multi-meter. Put the red lead on the "hot" lug of the sending unit, ground the black lead to the housing of the sending unit. Put the multi-meter on the 20 ohm range and move the float full sweep. It should read ~0 in the full position. The reading in the empty position will tell you what you need to know. I mis-read your initial post and missed that you still have the original gauges so my first reply may not have made any sense. If so sorry for any confusion.