Topic: Gas Gauge Creeps over the full mark -49 Mercury

Tracker    -- 11-17-2009 @ 6:17 PM
  The gas gauge on this like new 49 Mercury Sedan had been working perfectly when we were only putting 5/6 gals of fuel in. We filled it to near capacity with new fuel and the gas gauge has started acting up.

When the key is turned off, the gas needle returns to empty. When it is turned on, the needle starts to the top but when it reaches the top fill mark, it keeps on creeping past the mark until it goes to the full peg ...about a quarter past the full mark. Has anyone dealt with this problem before ?

Any suggestions would be much appreciated. Thanks .

TomO    -- 11-18-2009 @ 8:11 AM
  If your car has been converted to 12 volts, that is probably normal.


supereal    -- 11-18-2009 @ 9:21 AM
  Check to see if the body of the sender is properly grounded, and that the wire to the dash isn't grounded along its path. To check it, disconnect the wire at the sender terminal and turn on the key. If the needle still pegs, the wire is grounded. If it doesn't, the sender is at fault, and will need to be pulled from the tank to examine the float, float arm, and the slider. The 6 volt type should read 10-100 ohms, the 12 volt reads 40-180. As TomO says, if you converted to 12 volts, that is likely the source of the problem.

Tracker    -- 11-18-2009 @ 11:03 AM
  This 49 Merc is the proverbial little ole ladies car driven only on has 17,000 miles on the odometer and is still 6 volt.

Superreal ... I tried your remedy..the needle falls back to zero when key is turned off. I have the sender unit out and now I see that its been replaced at sometime or another so I don't know what I'm looking for. There is nothing obvious. How to test it out of the car ?

Thanks for both of your replies.


supereal    -- 11-18-2009 @ 12:02 PM
  If you have access to on ohmmeter, put it on the 1X scale, and clip the leads to the sending terminal and the body of the sender. As you move the arm, the meter should read from 10 up to 100 ohms as you move it from one extreme to the other. To test the wiring, disconnect the wire from the sender terminal and turn the key on. If the gauge needle swings over, there is a short in the wire between the sender and the gauge. If the gauge doesn't move, the sender is at fault. As the gauge does move, I wouldn't suspect that it is the problem. When you remove the sender from the tank, shake the float to be sure it hasn't leaked and partially filled with fuel.

Tracker    -- 11-18-2009 @ 2:30 PM

The paper work indicates the owner installed a MACs sending unit just last year. Its a cheesy looking sender but it did work at one time.

I see the float arm has never been shaped or bent. We put the ohm meter on it and it reads out like its working. When we put it back in the tank, with ground wire attached as well as sender main wire, it creeps right back over the top of the full mark. Does the float arm need to be bent or shaped in any way ? The tank is 7/8 full ...I don't have anything to compare the float lever arm ( float was a solid foam not absorbed with fuel ) original position to .


supereal    -- 11-19-2009 @ 8:27 AM
  I'd opt for a replacement sender. C&G has a good one, 01A-9275-6V for $45. We don't buy from Mac's, as too often their parts seem to be lesser quality. Maybe it is just us, but we don't seem to have a problem with other vendors, with a couple of exception.

TomO    -- 11-19-2009 @ 9:09 AM
  Tracker, I would try to find an original Ford sender. The replacement senders are of the variable resistance type and will never have the accuracy of the original King Seeley type.

The original type balances the current in the sender unit with the current in the dash gauge to give you a reading.

Advertise on this site, the V-8 Times and the Ford Barn site for an original type sending unit.


Tracker    -- 11-19-2009 @ 2:14 PM
  Thanks for your suggestions guys...I'm non plused to say the least that no one thought to tell us this car also had a replacement gas tank that has an odd number of sender mounting holes ..thus the MACS after market sender. The previous owner is even less of a mechanic than I am and did the work himself but I'll have to admit the sender did work while putting in 5/6 gls of fuel.

I see in the cataogs that Yogi's offers a 5/6 hole mounting plate that allows the changeover. I will order a new sender unit from C&G or if possible get a King Sealy from a used parts supplier.

Thanks to the both of you for your suggestions. I'll post a playback when all this is done.

TomO    -- 11-22-2009 @ 8:23 AM

The aftermarket tank may not have a big enough opening for the King-Seely unit. I bought a Drake replacement tank for my 40 and had to return it because the original sending unit would not fit.


supereal    -- 11-22-2009 @ 10:48 AM
  Most of the Drake catalogs state that the original sender will not fit their tank, and the Drake "universal" sender will be required.We have used that unit on 6 volt cars without problems, but they don't seem to offer different models for 6 and 12 volts, as do other vendors such as C&G. I assume you would have to at least add a series resistor for 12 volts to keep the gauge correct, as the 6 volt provides 10-100 ohms, the 12 volt, 40-180. Even so, it is unlikely the reading would be linear.

Tracker    -- 11-22-2009 @ 4:38 PM
  I was unable to locate a King Seely but did read that it works differently than the resistor gas gauge. It has a bi-metal strip that works in conjunction with the original gas gauge.

Now I know whats been done ie: Tank by Tanks, Inc, sender unit from MAC's, and a 1/8"depth adapter plate to accomodate the six hole after market sender.

I located an original used sender from a 51 Merc but the thickness of the 6 hole adapter appears to raise it too high in the mounting for it to make proper contact with the fuel . My next plan is to buy the C&G unit and hope for the best.

As always , I value everyones suggestions as thanks again for your help.


trjford8    -- 11-22-2009 @ 7:13 PM
  I have used the sender from Yogi's with good success.

supereal    -- 11-23-2009 @ 8:46 AM
  Almost always, the float arm of the sender must be carefully bent to allow the proper reading. It is done by allowing the fuel level in the tank to be used until it is nearly gone, the adjust the float just enough to touch the fuel.

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