Stranger fuel indicator issue

EdFred

EdFred

Taxi to Parking
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Feb 25, 2005
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White Chocolate
Last flight before topping off, and this flight this happened.
Equipment:
Original Piper fuel sender
EI MVP 50 engine monitor

Top it (left main) off, and it reads as full. Burn it down to 10 gallons or so and switch to another tank. Keep flying along and the fuel level keeps rising in the left tank. Give it a "shake" with the rudder or ailerons and it comes down to what I calculate it to be. But starts to climb back up to 17 to 24 gallons. Shake the plane again and it drops, but then starts climbing again.

On descent it stays down but on landing it goes to indicating what it should and stays that way until airborne.

It's only the left tank.

Thoughts?
 
Does the airplane have rubber fuel bladders? Venting problems can do it. Like a leaky fuel cap letting the low pressure atop the wing reduce the tank pressure so that the bladder gets sucked up, making the gauge float rise. Known to be a problem with Cessna 180/182/185 with the bladders. It can get so bad that the fuel is pushed out of that leaky cap, losing all the fuel while the gauge says the tank is getting fuller. It was the original flush caps that were bad for that. An AD was issued.
 
Dan Thomas said:
Does the airplane have rubber fuel bladders? Venting problems can do it. Like a leaky fuel cap letting the low pressure atop the wing reduce the tank pressure so that the bladder gets sucked up, making the gauge float rise. Known to be a problem with Cessna 180/182/185 with the bladders. It can get so bad that the fuel is pushed out of that leaky cap, losing all the fuel while the gauge says the tank is getting fuller. It was the original flush caps that were bad for that. An AD was issued.
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Comanche, so yes on the bladder. I will double check the cap, although it seals up good, so maybe a crack/ho,e in the top of the bladder causing it.
 
Back in the day I had a Cherokee 140 with an inop fuel gauge on one side. I hardly missed a beat with the discrepancy. I got by with knowing a known fuel quantity before departure, then managing tank selection. I would land selected to the side with the working fuel gauge.
That process may not work for the next, ok for me.


Of course, get things fixed at some point.
 
Some Comanches have a Recurrent ( 100 hr ?) inspection of the bladder

attachments unless the Vent System is modified. One particular aircraft

always had a couple fasteners unsnapped . I always wondered if that

happened on the first flight since the inspection or 99 hrs later.
 
Magman said:
Some Comanches have a Recurrent ( 100 hr ?) inspection of the bladder

attachments unless the Vent System is modified. One particular aircraft

always had a couple fasteners unsnapped . I always wondered if that

happened on the first flight since the inspection or 99 hrs later.
Click to expand...
Annual was just done last month and fuel cell inspection was complete.
 
EdFred said:
I will double check the cap, although it seals up good,
Click to expand...
There are two seals in the cap: one one you see that seals the cap into the filler neck, and the other is a much smaller one that seals the locking shaft.
sourdough44 said:
Back in the day I had a Cherokee 140 with an inop fuel gauge on one side. I hardly missed a beat with the discrepancy.
Click to expand...

§ 91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.​

(a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA-approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition.
(b) Visual-flight rules (day). For VFR flight during the day, the following instruments and equipment are required:
(1) Airspeed indicator.
(2) Altimeter.
(3) Magnetic direction indicator.
(4) Tachometer for each engine.
(5) Oil pressure gauge for each engine using pressure system.
(6) Temperature gauge for each liquid-cooled engine.
(7) Oil temperature gauge for each air-cooled engine.
(8) Manifold pressure gauge for each altitude engine.
(9) Fuel gauge indicating the quantity of fuel in each tank.

Fuel gauges are not deferrable items. A defective gauge makes the airplane legally unairworthy. This could be an insurance hassle if you had an accident.
 
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That plane was sold many years ago. I’m not sure if it was destroyed flying or possibly a weather event, MS. I do know, not related to anything to do with fuel indication.
 
Easy test will be to swap caps and see if the problem moves tanks or stays or goes away.
 
What Maule Skinner sez. Most likley, your fuel bladder is "getting sucked"...common things being most common....
 
IMHO A visual check is not enough, Removing the cap and blowing low

pressure air in is essential. Again; the bladder may be already loose.

Perhaps the bladder was not properly secured at the Inspection?
 
As mentioned before, venting issue probably is sucking the bladder. Needs to be addressed before flying.
 
Checked the fuel cap. I made the mistake of listening to someone and how much to (or not to) tighten. Left cap was in, but only semi tight, and I could spin in. Gave it a tightening like I had been doing the previous 15 years. Verified visually and agreed with the indicator reading. Flew it 45 minutes and there was 0 fluctuation.

Will have my AP do a quick check on the clips.
 
Last edited:
Dan Thomas said:
There are two seals in the cap: one one you see that seals the cap into the filler neck, and the other is a much smaller one that seals the locking shaft.

§ 91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.​

(a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA-approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition.
(b) Visual-flight rules (day). For VFR flight during the day, the following instruments and equipment are required:
(1) Airspeed indicator.
(2) Altimeter.
(3) Magnetic direction indicator.
(4) Tachometer for each engine.
(5) Oil pressure gauge for each engine using pressure system.
(6) Temperature gauge for each liquid-cooled engine.
(7) Oil temperature gauge for each air-cooled engine.
(8) Manifold pressure gauge for each altitude engine.
(9) Fuel gauge indicating the quantity of fuel in each tank.

Fuel gauges are not deferrable items. A defective gauge makes the airplane legally unairworthy. This could be an insurance hassle if you had an accident.
Click to expand...
hmm would think most ga aircraft should be grounded
 
I trust the pre flight fuel stick and use the fuel gauge as back up. But yes, do not fly if a fuel gauge inop. It’s listed a fundamental instrument for a good reason.

OP - congrats on thinking through the problem and solving it. Sometimes it’s the simple things that trip us up.
 
IIRC A “ quick check” would not be quick.

First the tank must be de-fueled and then the oval shaped adapter

can be removed. My recall is that is also contains the Sender. This does

present an opportunity to move the float manually and verify readings.

Possible Ohmmeter check?
 
MauleSkinner said:
Probably more like most GA pilots who believe old wives’ tales about fuel gauges should be grounded.
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so i'm guessing you'd be all in for getting in any random GA plane and flying to low fuel by only the fuel gauge ?
 
MackMooney said:
so i'm guessing you'd be all in for getting in any random GA plane and flying to low fuel by only the fuel gauge ?
Click to expand...
If I wouldn’t do it with a jet, a car, a motorcycle, or any other motorized contrivance, why would I do it with a GA airplane?
 
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As I can’t dip a fuel stick in the tank while in flight, the fuel gauge is what I have to work with. If it heads to empty, I might have a leak, lost a fuel cap, something. I need it working to fly safely IMHO.

I’m not flying if I can’t dip a fuel gauge stick in the tank AND if the cockpit fuel gauge instrument isn’t working.
 
When I de-fuel an aircraft I generally will check and see that when it reads

EMPTY that there is still fuel going to the engine. Not a real “ Calibration”

but somewhat accurate where it counts.
 
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