View Full Version : Fuel System: Gas gauge problem

08-02-2018, 12:53 PM
The gas gauge on my 1963 R1 Avanti only registers half full when the tank is full. I have tested the gauge per the shop manual's test and it will peg to full and I have pulled the sending unit out and the cork floats seem fine. Could this be an issue with improper ground connection? Any other suggestions? I hesitate to bend the sending unit rod severely.

08-02-2018, 12:58 PM
I can never hurt to clean the Sender Terminal and the Wire Terminal and run a ground wire from a sender screw to the Frame.

08-02-2018, 01:21 PM
The cork float may look OK, but the test is to put it in a container of gasoline and see if it sinks after awhile. The cork had a varnish finish on it originally and after many years and changes in gasoline, that finish may be compromised and the cork slowly soaks up the gasoline and doesn't float properly.
The simple fix would be to just replace the float with a replacement plastic or brass one and adjust the rod to read correctly when empty. The car will run fine if the gauge reads a little off on the top end, but if it's off on the bottom end, not so much.

08-02-2018, 07:22 PM
I will try that. Thanks. I presume I need to go to SI for a replacement float? or is there another float source you would recommend/type that would interchange?

08-02-2018, 08:22 PM
Any of the antique Ford or Chevy truck suppliers have brass floats for about $7 or so. Pull off the old cork, clean the swing arm carefully and solder a float onto it.

08-02-2018, 09:34 PM
I can never hurt to clean the Sender Terminal and the Wire Terminal and run a ground wire from a sender screw to the Frame.

I did this with my 62 GT when I was having a similar issue, problem solved!

08-02-2018, 10:08 PM
There is a low, and high end adjustment once the gauge is out of the housing. That is it should be factory set when the gauge was made. When I re-do them, I remove the bezel and lens and the mechanism from the gauge cup. Then I hook up the gauge to the correct sending unit, and run it through the sweep of the arm. Most time the adjustment is fine, but the needle is dry and bummed up on its pivot. The gauge can be calibrated to the sweep of the sending unit so empty =empty, 1/2= half way on the sweep, and full is the top of the sending sweep. The adjustment slots for both the high, and low ends of the needle are only accessible when the gauge is apart.

08-03-2018, 02:15 AM
My recently purchased 1950 Land Cruiser has the identical problem. I'll have to see if I can find the ohms reading for the tank unit, then use a rheostat with the same range to test the dash gauge. When I worked at the GM dealership I kept a 0-100 ohms rheostat in my tool box to test the fuel gauges.

08-04-2018, 10:26 PM
Today I removed my 1950 Land Cruiser tank unit, and found someone installed a universal unit. I had to bend a zigzag into the wire to shorten it about an inch. Then I had to raise the unit in the slot so the float now works the full stroke of the rheostat. The gas tank allows for the float to rise and fall about 6", but the universal unit would rise and fall about 8" or 9". The rheostat measured 4 ohms full up, and 100 ohms full down. This will help some, but my dash gauge still only shows 3/4 when it's full, so I'll have to replace the dash gauge also. I'm also going to install an original tank unit. Here's a picture before I bent the wire.


08-05-2018, 01:27 AM
Does the '50 Land Cruiser need a single-terminal or a two-terminal sending unit? Somewhere around 1950 is when they changed over to the single-terminal system. I don't know if it was across the board on all models, or on a model-by-model basis. I know some early 2R pickups still used the 2-terminal sender. Check and see if the harness to the tank unit contains a second wire.

08-05-2018, 07:16 AM
My 50 Land Cruiser doesn't have a separate ground wire, like my 50 Champion has.
The Champion ground may have been added when the car was restored about 26 years ago.

08-05-2018, 09:24 AM
To be clear, the 2-terminal sending units were grounded at the tank, and both wires carried forward to 2 terminals on the gauge itself. The wiper on the resistance element was grounded, and the ends of the resistance element were connected to the 2 terminals. So as the float moved through its range, resistance to ground at one terminal increased, as it decreased at the the other. If there aren't two wires bundled together in the harness going to your sending unit, it's likely the car had a single-terminal sending unit since new.

08-05-2018, 05:39 PM
Yes, both my 50's have a single wire sender. I just returned home from the surplus store looking for a 100 ohm rheostat, but they didn't have any. Anyway, when I ground the sending wire the dash gauge will only go to 3/4 full, so that tells me the dash unit is bad. I have a spare dash unit, and will compare the ohms between the two.