mooney bravo 1998 tls fuel gauges

[pkofman]

Can someone here please tell me how the fuel gauges ( stock ship -analog ) work on the bravo and where are the gizmos that measure fuel in each tank?  My  gauges seem to give false readings fluctuating to half tanks and then back to full, all in a period of minutes. Maybe something is physically stuck or misbehaving. Where are they located, and can I simply move or tap the wing to get things moving correctly again? I have a shadin and edm, so I get total fuel flow and know exactly how much fuel I have, but I want confirmation from the ship gauge. ( the plane's original gauges are pretty inaccurate; thankfully, the shading does a great job, but I wonder if there is an easy fix if the original devices are simply stuck!   thoughts 

[LANCECASPER]

5 minutes ago, pkofman said:

Can someone here please tell me how the fuel gauges ( stock ship -analog ) work on the bravo and where are the gizmos that measure fuel in each tank?  My  gauges seem to give false readings fluctuating to half tanks and then back to full, all in a period of minutes. Maybe something is physically stuck or misbehaving. Where are they located, and can I simply move or tap the wing to get things moving correctly again? I have a shadin and edm, so I get total fuel flow and know exactly how much fuel I have, but I want confirmation from the ship gauge. ( the plane's original gauges are pretty inaccurate; thankfully, the shading does a great job, but I wonder if there is an easy fix if the original devices are simply stuck!   thoughts 

It could be time to rebuild your senders or it could be a loose connection on your wires, but either way you need to find out. The airplane is not legal to fly without 2 working fuel gauges on the instrument panel. (see page 2-10 on your M20M POH)

Your Shadin is a nice option and provides advisory information, but is not a certified gauge. While very accurate in telling you how much fuel has gone through the transducer, if you have a leak at your pump or in your connections you will not know how much fuel you have. Thankfully the sight gauges on the wings show you the last 30 gallons on each side. 

[pkofman]

15 minutes ago, LANCECASPER said:

It could be time to rebuild your senders or it could be a loose connection on your wires, but either way you need to find out. The airplane is not legal to fly without 2 working fuel gauges on the instrument panel. (see page 2-10 on your M20M POH)

Your Shadin is a nice option and provides advisory information, but is not a certified gauge. While very accurate in telling you how much fuel has gone through the transducer, if you have a leak at your pump or in your connections you will not know how much fuel you have. Thankfully the sight gauges on the wings show you the last 30 gallons on each side. 

well, they  do work i just dont like how they fluctuate and given how they are not very granular or lack fine precision in their reading they just seem generally inaccurate to me , I've  had this issue on many of the mooneys ive owned as they do not appear to be  very precise. The other question I have is do the analog gauges fluctuate much due to the aircraft position while flying ( I never really thought about that much ) but my tks fluid for example shows very different values in the air vs the ground. There  is even a calibration chart from CAV for this issue ( tks). So, would you expect the fuel gauges to show a discrepancy on the ground vs in-flight

 

Edited February 23, 2024 by pkofman
spelling

[Pinecone]

There are two senders in each tank.  One on the inboard end, accessible by removing some interior parts.  The second one is mounted at the outboard end of the tank, accessible through an inspection plate.

The wiring comes from the gauge to the inboard sensor then to the outboard then to ground.  So they are wired in series.  The inboard sensor is electrically isolated from the tank.

IIRC, each sender is a potentiometer giving 0 ohms at empty and 30 ohms when full.  So when the tanks are full, the gauge "sees" 60 ohms ground.

It they are bouncing around and changing, it could be loose wiring, an intermittent ground (either a ground at the inboard where there should not be or no connection to ground at the outboard end).  Or the senders units are worn and need rebuild.

Another option is to replace them with Cies senders.  They can work with your existing gauges, but best would be to install some digital gauges and use them in digital mode and they are VERY accurate.