Fuel Tank Sender

[Brakin80]

About to tackle the fuel tank sender. Tested electrical system and it's fine. Either the float is full of fuel or the unit is pooched. Can you repair them? If not, what do I replace it with? An NOS Smith's or a Moss Motors? Is there a difference? Thanks

 

[Dave Russell]

Try a couple of tests. Disconnect the wire from sender to gage, at the sender. Ground the wire coming from the gage. The gage should read empty or a little below. With the wire ungrounded the gage should read above full.If not, the gage or the wiring are defective. You can isolate the back of the gage & do the same tests to find if it is the gage or the wiring.

Measure the resistance from the isolated sender terminal to ground. with the tank full there should be around 70 to 80 ohms. With the tank empty the reading should be around zero to 7 ohms.

It may be easier to remove the sender for tests. Be prepared to replace the cork seal around the sender & there should be copper washers under the sender securing screw heads. Permatex "Hylomar HPF" is a good sealer to use on the gasket & screws.

Obviously there should be no fuel in the brass float. If there is, drill a small hole in it & drain. Solder the hole & submerge the float in hot water. Air bubbles will come out wherever the leak is. Solder the leak & retest.

As you move the float arm from empty position to full the ohmeter connected from sender terminal to ground should change smoothly from around zero to 70 ohms. Sometimes the arm can be making a poor ground contact on the sender body & cleaning or tightening the arm pivot can help. There is a small resistance wire coil that the arm travels over which gives the resistance changes with arm motion. It is pretty hard to repair the tiny wire but it can sometimes be done.

If you get a new sender (Moss is as good as any) do the same tests before installing things. There is a way to precisely calibrate the gage itself if everything is ok & the gage is just a little off. If the gage needs repair go here;
Margaret Lucas
Mo Ma Manufacturing - instrument repair
13211 Second Street. NW
Albuquerque, NM 87102
Ph (505) 766-6661 - Fax (505) 766-5419
momanm@aol.com
D

 

[Michael Oritt]

While we're on the topic of sunken senders I'd like to pose an issue for which I have to believe there is a solution:

Would it be possible to fill fuel tank senders and/or carb floats with closed-cell floation--something that will NOT absorb gasoline and sink due to a pinhole? I've wondered whether I could buy one of the plastic carb floats, drill a big enough hole in which to inject either the one-part expanding closed-cell foam such as is used for sealing windows or the two-part used for boat floatation, seal up the hole and eliminate just one more source of potential problem.

Any thoughts out there?

 

[bighly]

I actually did use a wine cork for the trip to the Eureka Rendevous last year. 1996 Clos Du Bois Merlot to be precise and an excellent year at that. Beat not having any bounce in the gage while I waited for my new one to arrive (was home when I returned). One trick to try is to use fuel resistant hyloymar (SP?) gasket sealant and DO NOT OVER TIGHTEN. The rubber gasket will squeeze out like a trout. Expect that your gage will bounce with the sloshing of fuel, this is normal.

 

[Dave Russell]

I guess you could. For a carb, the result would have to have the nearly the same bouyancy (weight per volume) as the original to keep proper calibration. It also would need to be very near the original size in order to fit.

I suppose that for no more accurate than the gas gages are, a bottle cork would work. Your favorite wine DOES have a cork, I hope.

Won't go into never having had a float fail. Heard about it a few times though.
D

 

[Johnny]

Excellent advice from all of the above. I just bought a NOS on ebay for about $70. Works very good. I took my old one apart just to see what's there. The wire armature Dave mentions had a broken wire at the end going up to the terminals. Yes you could solder it being very careful, but I also noticed another broken wire around the armature itself. When I tried to solder it, it just left a glob of solder (not good). So, I gave up on it. It's a simple device with the float attached to an arm with two copper contacts that ride along each side of the armature. If memory serves the resistance varies with where along the armature the contacts are riding. If there is no contact, you have no reading. One thing I was confused about was the opoening in the housing where the float came entered. Gasoline surely would be able to enter also. Wouldn't that fowl up the operation?
I do remember someone telling me that when you re-install the unit to adjust the float to allow about 2 gallons of gas to be in the tank upon showing empty on the gauge. That way, you'll never be caught short.

 

[Brakin80]

Johnny - I noticed that you used the side curtain mount for your side mirrors. We've been wanting to do the same. At least on the drivers side. We can't bring ourselves to drilling holes in the fenders. What mirrors did you use, and did you have to make any modifications?

 

[Dave Russell]

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by Johnny:
One thing I was confused about was the opening in the housing where the float came entered. Gasoline surely would be able to enter also. Wouldn't that fowl up the operation?

<hr></blockquote>
Yes- There IS gas in the sender. Gas in an electrical insulator & it actually may provide a little lubrication for the moving parts. The electric current levels in the sender are purposely limited to a value that is too low to cause a spark ignition in the tank. "Shades of Flight 800", at least that was the FAA story.

Actually, thousands/millions of cars have used a similar setup without explosions. It wouldn't be wise though to alter the circuit such as accidentally getting the sender to gage lead connected directly to the 12 volt supply, as an internal short circuit in the dash unit might cause.
D