What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Help SW Fuel Sender problems

Rick_A

Well Known Member
I can't get one of my SW fuel senders to work while it's in the tank. The right sender works fine. The left sender resistance does not change when I add fuel.

The sender works fine when I pull it out of the tank and hook it up to my guage. I pulled it out once and re-installed it. I checked the float arm measurements per the plans (3.25" on the long arms). It appears to be oriented correctly. The float is facing forward. I have a good ground with a wire connected directly to the sender plate.

After I re-installed it, I had the exact same problem - no change in resistance with 13 gallons in the tank. I've now pulled it a second time (and yes, I did use proseal both times) re-checked everything again and can not figure out what's wrong.

Any suggestions would be appreciated. Thanks.
 
Last edited:
Two things to try:

1) Remove the fuel strainer from the tank. Push a clothes hangar through the hole and use it to move the float. See if it is stuck or something.

2) Create an independant ground path from the sender to the fuselage. It may be that the proseal is preventing a sender to airframe ground. You could use a ring terminal from one of the screws on the outside of the sender and attach the other end of the wire to something on the fuselage just to test things...
 
4th time is charmed

I finally got my sender working today. I verified the geometry of the sender arm in Scott Card's -8 tank that was in the ideal state of completion to verify the float arm bends were correct.

When I did a "float test" today, it seemed that it the breakout force to get the arm moving was just a little high. Since the 3/4" bend that locks the arm in place is on the axis of rotation, I thought that it might be adding a little drag to the mechanism. I shortened it down to about 1/2" which is plenty to lock the arm in place and it did seem to reduce the drag ( there appeared to be a very slight curve in the end so cutting it off probably helped to reduce friction). I also tweaked the bend on the long arms a tiny bit which seemed to help the float start the arm moving.

It's hard to believe that these very slight changes made the difference but it's working now so I'm a happy guy.
 
Wow, but Yee Haw!!!
We talked about these things. I knew the "float test" would be yield some useful information, however I'm amazed that the difference in breakout force mattered. Tip to others, make sure your float is totally free to swing. The difference that Rick is talking about is almost imperceptible.
 
My right hand sender was sticking, not free as it should be. When I added fuel to calibrate the Dynon EMS D-120 gauge, the float quit moving (no resistance change) after 4 gallons had been added. Pulled the sender (major PITA), and using 600 grit sandpaper, I polished the 3/4" part of the arm that rotates in the plastic bushing. The sender now works like a champ. I suspect that if the geometry ain't perfect, or if in the bending process the rod gets smashed out of round, it can bind. In any event, the polishing job has mine working great. :D
 
Leaking float

I also had a problem with my left sending unit. From assembly pictures I realized I mounted the float backwards in the wire bracket. Apparently this caused it to hang-up. After removing and correcting this, it still did not work. Today I pulled it out again and confirmed that the brass hollow float leaked and was full of fuel. A quick test with a cup of fuel confirmed that it did not float. Now I have to call Van's to see if they sell the float seperately.

FYI: In another post there was a question on how much fuel is unusable. I have found that when I ran the fuel in the right tank down to exactly empty it took 18.6 gal (19 published capacity) in the RV-6 tank to fill it up. In the left tank I ran it dry once and it took exactly 19 gal to fill. Vans is dead on on volume for the RV-6 and I'm sure also are on the other models.
 
I'm having fuel guage problems too. I've got an RV9A and I'm the third owner, not a builder. My gauge is through a g3x touch. The gauges do not work right. Sometimes they move and sometimes they don't and they are never accurate. I tried grounding the sender to the airframe, no change either side. I tried disconnecting the wire to the sender and there was no change in guages at all on either side. They are float type senders - I think the "normal" one for the 9. Is this possibly a G3X setup issue? Is seems crazy that neither Guage changed when I disconnected the wires or grounded them to the airframe using a piece of wire.
 
Leaking Float

Frank,
PM your address to me, I will send you a new float with un-bent wire.
Ron
 
I'm having fuel guage problems too. I've got an RV9A and I'm the third owner, not a builder. My gauge is through a g3x touch. The gauges do not work right. Sometimes they move and sometimes they don't and they are never accurate. I tried grounding the sender to the airframe, no change either side. I tried disconnecting the wire to the sender and there was no change in guages at all on either side. They are float type senders - I think the "normal" one for the 9. Is this possibly a G3X setup issue? Is seems crazy that neither Guage changed when I disconnected the wires or grounded them to the airframe using a piece of wire.

Probably a failed sender. It is just a pot with a wiper going over a carbon trace and can intermittently fail open, which would explain some of your symptoms Best to put an ohmmeter on the sender and get the float to move. If I remember correctly it is 330 ohms at the bottom of travel and 30 ohms at the top. Should be able to find it on the internet. This series of senders was used on most cars made in the 60's & 70's. In an RV, you will not see the full range os the senders travel.

The fact that sometimes they move and sometimes they don't points more stongly to a sender or wiring issue than a config issue.

Larry
 
Last edited:
Back
Top