Safely working on gas tank


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By jrw429 - 13 Years Ago
I've got a fuel gauge that behaves erratically. Wild swings in the needle, and especially unreliable once it reaches 1/4 full. The previous owner put a modern round gauge in the dash where the original would be. It looks good, and I have an original dash and gauges for possible original restoration later. Because of the new gauge, I am thinking the problems are with the sending unit. Could be wiring, voltage regulator, the new gauge, etc, but my guess now is sending unit.



My main question is how to safely work on the gas tank? What precautions to take when removing and inspecting the sending unit. Should the tank be full or empty? I don't want to go up in a ball of flames.



Next question is how to deal with the sending unit. I have a 57 Country Sedan. I've found new replacement sending units, but they all say "not for wagons". I had one person mention that I could get a new sending unit and simply bend the arm to match what the wagon needs. Is this true? Or is it more likely that just a new float would be needed. And advice on floats? There seem to be several choices - solid, brass, plastic, etc.
By msmith946 - 13 Years Ago
First. Check wire on sender. Sand both sides of connection with emory paper. Many times it is inaccurate becausse of increased resistance thru wiring. Check ohm reading of wire. Not sure of what ohm reading of sender is.


By msmith946 - 13 Years Ago
First. Check wire on sender. Sand both sides of connection with emory paper. Many times it is inaccurate becausse of increased resistance thru wiring. Check ohm reading of wire. Not sure of what ohm reading of sender is.


By Ol Ford Guy - 13 Years Ago
FWIW...I worked at a Ford Dealership, salesman, from 64-66.  They were working on a 64 Thunderbird gas tank.  While they were draining the tank, the car was on a hoist, the work light feel on the floor,  When the light bulb broke, it started a fire.  The fire department and techs with fire extingishers put it ouit.  After that, all the service lights were the tubular type with rubber cushioned ends,  So, I would use a safe type service light and have a good fire extingwisher on hand.
By paul2748 - 13 Years Ago
First of all, it is not the liquid that burns, its the fumes. So unless you can get rid of the fumes there is always the potential of danger. It almost impossible to rid an old tank of fumes. Even an empty tank has fumes. As was mentioned, use a light that won't break if dropped. No matches eitherSmile.



There are four things that can screw up the readings. A bad gauge, a bad sending unit, poor connection and a poor ground.



To check for a poor ground, make a temp ground wire and ground the tank. See if it works. Clean the wire and its connections as was mentioned earlier.



Checking the sending unit is harder. You need to check resistance with a meter, you have to know what the reading should be. I can't help there.



If I remember correctly, you can check the gauge by grounding the wire at the sending unit. if the gauge moves, it usually means it's ok. I hope someone will confirm this.
By ray - 13 Years Ago
Random thoughts on gas tanks. Work with lots of ventilation. Fuel fumes will collect in a low area. A fan will minimize the fumes from collecting. A full tank will have fewer fumes and fumes are what are dangerous, easily ignited..A full tank is just about impossible to handle if you try to remove it. Your tank may or may not be grounded through the mounts and straps. A separate ground wire could not hurt. Reproduction replacement brass floats are readily available and cheap. I've replaced a couple in old Ford truck the past year and quality looks good. The wiring coming from the sending unit has a pair of wires in a single cover, one of them is a ground. I've seen the ground wire broken inside the cover from the sharp angle it was routed. I've found most ground wires come out of the cover and mount to the vehicle frame within a foot of the tank. Make sure the ground is making good clean contact with the frame. A quick test of the dash gauge and wiring to the tank is to ground the wire to the sending unit to a clean spot on the frame. The gauge will show full. If you have a replacement sending unit in hand, hook it to the system wiring and see what the various positions of the float lever does the the gauge. I don't really know the difference between sending units on a car and wagon but electrically they'll be the same. Have fun, stay safe.Smile
By Frankenstein57 - 13 Years Ago
The wagon and ranchero share the same platform, and the wagon had a recessed area in the bottom of the trunk , for the spare tire. This cut into the gas tank size on these two cars, I think its 16 or 17 gallons. Although the 300 sedan is a similar vehicle, in wheelbase , I believe the tank is bigger and fills from the rear. The ranchero had its spare behind the seat, but still had the small tank.
By Oldmics - 13 Years Ago
Just went thru all this while repairing the fuel tank gauge on my 58 Edsel Roundup.

Essentially the 58 Edsel Roundup is a 57 Ford 2 door wagon. Same fuel tank as your Country Sedan and all of the rest of the Ford wagons.The Ranchero also uses this same fuel tank.

The fuel tank float sending units for the Ford wagons and the Ranchero are impossible to find.No one makes a reproduction unit.

The usual ohmage of the Ford fuel tank sending units read from 75 - 10  OHMS.

While I cant confirm this next statement but I believe that the wagon/Ranchero tank sending units do have a different measurement than 75 - 10. I have never had  a good original tank unit availiable to extract that information from.The ohmage difference is just my opinion based on my calibration attempts.

I can confirm that the sending unit in the tank has to work in tandom with the resistance of the dash fuel gauge.If the tank sending unit resistance is incorrect the dash gauge will be inaccurate.THIS PIECE OF INFORMATION IS VERY IMPORTANT!

There is a difference in the tanks sending unit float arms length when comparing the wagon/Ranchero unit to the normal passenger car tank sending unit.The wagon/Ranchero float arm is much longer.

I compared a new reproduction tank sending unit for the passenger cars to my used non working wagons unit.

I calculated the length differences where the float arm rested on the old original compared to the repro.I then cut off both the original and the repro float arm. I then soldered the old longer float arm onto the new repro sending unit.

This gave me a working fuel tank sending unit BUT it was no where near proper calibration on the dash gauge.I believe this is due to a difference in the repro tank sender having a different ohmage then what a wagon requires and also the float arm being not quite bent right.

With the tank out of the car and a jumper wire attached between the tank sender and the wiring harness,I put in 5 gallons of (non flammable) water.Its a 20 gallon tank so it should read 1/4 tank or close.

The dash gauge hardly moved off of empty.I made sure that the tanks sending unit float arm was in a reasonable floating position in  the fluid in the tank.I did this to make sure that it was not a float arm position error within the tank.It still showed way lower than 1/4 tank.

I started adding resistance by wire clipping a resistor placed in line between the tank sending unit and the wiring harness.

After a few incorrect trials of different value resistors, I came up with adding a 30 OHM / 10 watt resistor inline to get the proper calibration on my dash gauge at 1/4 of a tank.

Of course I checked it at half and a full tank of fluid also.Thats how I settled on the use of the 30 OHM resistor.It reads proper at full,at 1/2 and 1/4.

I"m not gonna run it below a 1/4 and empty to explore the accuracy of the gauge in that region.w00t

There is also the combination of bending the tank sending unit float arm to the proper position where it rides on the fluid to get the correct calibration.

I ended up perminantly installing that resistor in the spare tire area which is where the fuel tank sending wire runs thru.Built a small non electrical conductive cover for it ,imbedded it in silicone and all is well!

Yes,it was a PITA but its done and works great.

Hope this helps.

Oldmics

By 58rancho - 13 Years Ago
As to the float, I have a 58 Ranchero and the Ford dealer in town sold me a brass float (in stock!) that works fine in my new tank. I don't know how accurate it is, but it does work. I took what was left of the old one in with me. Good luck!
By jrw429 - 13 Years Ago
Thanks, awesome information, as usual. I'm in the midst of a Thanksgiving road trip with the wagon. 700 miles to get out here, maybe another 700 to get out to see more relatives, and then another 700 home. My (not definitive) research says that the tank should be 20 gallons. I ran it to below empty yesterday and it took 13 gallons to fill. The most I've ever put in was 14 when I bought it. I've been filling at 1/4 full on the gauge, which ends up being about 6 or 7 gallons.



I'll have a project for when I get back home.
By Rono - 13 Years Ago
Jim;

I also have had problems matching the sending unit to the fuel guage. When I replaced my stock guages with Haneline guages, the factory Ford sending unit was not calibrated with the correct resistance for the new guage. I had to get a universal Haneline sending unit and cut it down to size for my Customline tank.

Also, FWIW, I worked in the HAZ MAT emergency response field when I lived in Idaho. The guys the install and remove petroleum UST's (underground storage tanks) often used dry ice to chemically inert the empty tanks of vapors before they remove them and cut them up. You can get dry ice at many supermarkets. If the tank is free from any petroleum sludge, the dry ice will force any vapors out of the tank as it goes from it's solid state to CO2 vapor.

Good Luck!

Rono

By SkylinerRon - 13 Years Ago
Most aftermarket guages use the GM ohm scale. Fords are opposite (think backwards).

Goodluck,

Ron.