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  #1  
Old 11-12-2018, 06:38 PM
Atanyspeed Atanyspeed is offline
 
Join Date: Mar 2009
Location: San Diego, CA
Posts: 56
Default Fuel Level Sender Issue

Iím having any issue with my Stewart Warner senders units. From the day I started calibrating the units they have never giving me a consistent reading. One tank will only show a fuel level when it reaches 15 gallons. So I decided to pull the sender today and found the unit was very stiff as it moved through itís range. I put in another unit and during calibration it stopped registering after 4 gallons. I added 10 gallons more, no change. I pulled that unit and put the float into avgas to see if the arm on the sender moved and it didnt. Has anyone had problems with these senders binding up. All my electrical connections have checked out ok.
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  #2  
Old 11-12-2018, 08:40 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,862
Default

I don't know if it is related to your issue or not....

It is fairly common for the fuel senders to have enough friction that they will not change to the correct level when the airplane is static with no vibration.

When the engine is running, there is a lot of vibration in the airframe. Even if it is a very smooth running engine. This vibration enables the sender to properly move to the proper level.

When I do fuel system calibrations, I smack the tank skin repeatedly with my hand until the sensor value indication on the calibration screen stops changing. Add more fuel..... and repeat, until you have all of the calibration points you desire.

When the engine is running, the sender will be able to move properly, and as they have some use, they seem to loosen up a bit as well.

An interesting and somewhat related subject is the instrument panel vibrators that were used on instrument panels during the dawn of the jet age. The airplanes were so smooth that the analog instruments in the panel were no longer accurate because of the small amount of internal resistance in the mechanisms and the lack of vibration to help overcome it.
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  #3  
Old 11-13-2018, 06:01 AM
mturnerb mturnerb is offline
 
Join Date: Apr 2015
Location: Ponte Vedra, FL
Posts: 767
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Good point from Scott. I replaced one of my Stewart Warner senders from Vans prior to installation (easy to find at any automotive site) because I thought it was substantially stiffer than the other one.

I never considered the normal vibration/movement though.
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