Fuel gauges stink: fact or fiction?

drotto said:
I1. The FFA requires a fuel gauge in a plane. With how strict they are otherwise, would they really go as far as requiring a pilot to have and use an instrument deemed unreliable?

2. In primary training the number one lesson we are given in battling spacial disorientation is trust your instruments!!! They will save your life, and they are more reliable than you are when encountering IMC conditions. IFR is then completely based on "tech" to make it work and keep it safe. Yet the fuel gauge is the one we are told to be careful of.
Click to expand...

You're taught to trust your instruments, not your instrument. Every instrument in you cockpit is potentially unreliable, and that's why you always have multiple instruments for each and every function.

You fuel guage is no different. It is a single measure of fuel quantity. I automatically distrust anything that can only be determined from a single source. Fortunately fuel quantity is not. I can determine it just as well from a ground observation, along with fuel-flow and time.
 
Mine are pretty accurate and even better TRUSTWORTHY! I have a SIGHT GUAGE!!!
And I know how to read it!

I play a guessing game on how many gallons I have to buy. If I am within one gallon of right, I get a candy bar! I get candy bars frequently!
 
MyassisDragon said:
Fact and Fiction - some maybe, some newer ones maybe not... but most older planes I have flown IE- factory mooney's, Grummans, cennsas and pipers, all seem to be suspect to a point that I would never jump in the plane look at the gage and say "Hey I have 1/2 of a tank" then go fly using endurance based on that.

My opinion - Always dip the tank (even the AA5B can use a calibrated dip stick) and do you own endurance calculation and fly by time, not what the little gauge thing says. Unless it drops to zero during the flight, then I would question it.

I have had a few rental planes still show 1/4 or 1/2 tank when it was empty and a few would change to zero when I tap on them abruptly.

And of course, if you have a totalizator that's a different story, but we were talking gauges..
Click to expand...

True. The CFI should have gone over this carefully. Many light aircraft have faulty Gage's. Dipping with a stick should always be done. I flew a sundowner once when I had about three hundred hours. I came close to killing myself trusting the gas gage. It was wayyyy off'.
,
 
Affirmative OP. FACT.

The fuel gauges in the skywagon suck donkey units.
 
txflyer said:
Affirmative OP. FACT.

The fuel gauges in the skywagon suck donkey units.
Click to expand...

I wonder how many aircraft would pass if checked.

Fuel quantity gauges shall be calibrated to read zero during level flight when the quantity of fuel remaining is equal to the unusable fuel supply defined by 3.437.
 
bnt83 said:
I wonder how many aircraft would pass if checked.

Fuel quantity gauges shall be calibrated to read zero during level flight when the quantity of fuel remaining is equal to the unusable fuel supply defined by 3.437.
Click to expand...



Checked as in how? Never mind, I see you edited it in... :redface:

At annual time, the wagon passes because it's just a given that the gauges suck.

I compare ours to an old Chevy truck I used to have. It takes forever for them to come off full, but when they do, they go down quick.
 
txflyer said:
Checked as in how? Never mind, I see you edited it in... :redface:

At annual time, the wagon passes because it's just a given that the gauges suck.

I compare ours to an old Chevy truck I used to have. It takes forever for them to come off full, but when they do, they go down quick.
Click to expand...

Only reason I brought this thread up is that I'm working on putting two fresh senders and a new Aerospace Logic FL202 STC'ed primary fuel gauge in. The gauge I'm sure is top notch but it will be limited to whatever the senders can read. I don't recall specifics but I'm pretty sure it takes about two gallons before the floats move in this airplane.

So I'm pretty sure the new gauge will be accurate when fuel level is(guessing) above 2 gallons or below 23 gallons. Anything outside of that (25 gallon tanks) it will just read empty or full.
 
Last edited:
LDJones said:
Sometimes in some airplanes. But a week ago while ferrying a plane to FL the totalizer was telling me I had almost two hours of range left when the low fuel warning in one tank came on. Not in the mood to bet on either, I stopped and had less than :45 left in the tanks. Turns out the totalizer had been "ball parked" but never refined with real world data.

Lesson learned. Never assume unless you have personal experience with the particular aircraft.
Click to expand...


I can tell you this, from full tanks, and properly reset when full, when mine says I have used 25 gallons, the gas pump reads the same within .3 gallons. Always.

But if you do not set it to full tanks after a fill up, you can run into your situation.
 
txflyer said:
Checked as in how? Never mind, I see you edited it in... :redface:

At annual time, the wagon passes because it's just a given that the gauges suck.

I compare ours to an old Chevy truck I used to have. It takes forever for them to come off full, but when they do, they go down quick.
Click to expand...

:rofl::rofl::rofl:
 
bnt83 said:
I wonder how many aircraft would pass if checked.

Fuel quantity gauges shall be calibrated to read zero during level flight when the quantity of fuel remaining is equal to the unusable fuel supply defined by 3.437.
Click to expand...

That reg is often mischaracterized as meaning "the guages only need to be accurate when empty" when it actually means that "E" needs to be not empty-empty, but no useable fuel.
 
Fuel management in a plane is a top concern for me but I fly with minimum fuel. Long ago I made my own dip sticks by starting with zero usable and adding five a side and making sticks to indicate what was in there. My sticks have proven accurate over and over again. I had stock Cessna gauges and switched to new senders and Aerospace Logic digital gauges. I have mixed reviews on that. A Cessna tank is difficult to gauge. Accurate reading of fuel quantity in a crazy environment has shortcomings. That led me to add a FS450 totalizer. That helps but also isn't perfect. Factory K factor was spot on but my failure to correctly adjust it for added fuel is a problem. Like I said, I never fill my tanks. With my deadly accurate fuel gauges and deadly accurate flow instrument I still rely on my dip stick and a watch as my primary fuel management tools.

The best fuel gauges I know are sight gauges in the wing root of a Cub.
 
Zeldman said:
The fuel gauge is only required to be accurate when the fuel tank is empty. Does that make you feel better..?? :lol:
Click to expand...

As I suspect you know, that is an old wive's tale.

Fuel Gauges are required equipment by the FARs. A different FAR requires all gauges to be accurate. Unfortunately there is no definition of accurate....

"Accurate when empty" is actually a point of calibration. Gauges are designed to show zero fuel remaining when there is no usable fuel remaining. Overlooking the definition of accurate for a moment, it is nice to know that 'zero' on your C-150 means the same thing as on your C-130 Hercules

-Skip
 
Fearless Tower said:
I thought his issue was not being able to reach the fuel selector to change tanks?
Click to expand...

The way I understood when I read it was that multiple issues compounded.

1) He couldn't see the fuel level, even though it was a sight gauge because it was behind the pilot's seat. The mechanic supposedly mounted a little mirror in the cockpit for him.

2) He couldn't reach the fuel selector, even after he and his mechanic tried to attach some vice grips to it in order to extend the selector. It required the pilot to rotate 90 degrees in the seat to change.

3) The mechanic told him very clearly he only had X amount of fuel left, and they pushed him to take on more fuel. He declined, saying he wouldn't be up that long, and he should have plenty.

Wholly and completely irresponsible, something that could have been prevented in so many ways.
 
My fuel gauge is on my wrist. Been that way for over 50 years. Hasn't failed yet. Nothing is perfect, but this method seems reasonably close.
The gauge on the panel is a back up indicator - and a warning device if the reading is changing faster than the watch - the watch is primary otherwise.

Now as to accuracy when empty: My outboard tanks are reasonably close (actually show empty with a bit less than ten minutes of fuel left - I know because I run them dry often)
The mains, I haven't a clue. They have gone below one hour of remaining fuel maybe twice in 15 years -and that was by 8 or 9 minutes at the most. The gas I put in suggested that the gauge was within two gallons of being accurate.
Close enough for government work - and I hope never to test it. .:D

Just had this discussion on Tugnuts recently (Ranger Tug owners group). Fella was all bent out of shape that he ran out of fuel while there was still a some showing on the gauge. While there were a few loose thinkers blowing opinions out of their nether regions, most of the tug owners I consider competent bluntly told him to start using the engine hour meter (a clock) for tracking fuel burn.
 
Dr. O said:
My fuel gauge is on my wrist. Been that way for over 50 years. Hasn't failed yet. Nothing is perfect, but this method seems reasonably close.
The gauge on the panel is a back up indicator - and a warning device if the reading is changing faster than the watch - the watch is primary otherwise.
Click to expand...

This is what I was taught, and I'm sticking to it. Also verifying fuel level during preflight, fillup, etc. I've really got to have a look in the tank prior to takeoff.
 
TheTraveler said:
This is what I was taught, and I'm sticking to it. Also verifying fuel level during preflight, fillup, etc. I've really got to have a look in the tank prior to takeoff.
Click to expand...

Exactly. Check you fuel before you launch. Calculate your consumption every time you fuel and watch your time.

A lot of talk about using totalizers, but I have seen them give erroneous info too.
 
Fearless Tower said:
Exactly. Check you fuel before you launch. Calculate your consumption every time you fuel and watch your time.

A lot of talk about using totalizers, but I have seen them give erroneous info too.
Click to expand...

We had a thread about this sometime in 2012 or 2013. I remember posting my strong opinion that I will never fly without actually climbing up and looking into the tank during preflight or prior to takeoff. A few thought I was crazy, but right back at them, IMO. I have not yet been in a situation where I wasn't able to open the tank and verify (commercial riding aside).
 
I trust my gauges, and my totalizer, but eyes-on is the enabler of the other two. Gauges are a gross indicator, totalizer is dead-nuts accurate, but if I did not see the gas in the tanks, I could be starting out several gallons low, a difference which might or might not be readily apparent on the gauges.
 
The shop manual for my Beech Sport 19 states "Fuel gauges register full whenever a quantity greater than 20 gallons is in the tank." The tanks hold 30 gallons each. I could not find this in the POH, still looking, but it is correct. I did find in the POH you should not take off with 10gallons or less in each tank (4 gallons unusable per tank).I know my fuel burn, visually check each tank, and use my (tachometer/hour meter) as a time devise. Don't trust my fuel gauges!!!
 
Last edited:
Wow, sure are a lot of defective fuel indicators out there. I have a gauge. It's accurate. It's been tested at all cardinal points on the gauge. I've dipped the tanks to verify. I use the gauge at it was designed, to indicate the fuel remaining in the tank.

If it should break in flight I would land and have it repaired, just like anything else.
 
Any fuel situation should require two methods for verification. Keep a running total would be a first one. Example being we took off with 40 gallons (known) burned 20 for the flight and 20 remains. Refilled with 25 gallons, departed with 45 and burned 15, ended with 30 in the tank.

Second method of verification is in the form of a fuel gauge or totalizer. It should agree with the first method (plus or minus a small number). If either method is showing more than an appreciable difference then there is a problem.

The third point of verification comes by fueling with a known quantity (such as tanks full).
 
bnt83 said:
Only reason I brought this thread up is that I'm working on putting two fresh senders and a new Aerospace Logic FL202 STC'ed primary fuel gauge in. The gauge I'm sure is top notch but it will be limited to whatever the senders can read. I don't recall specifics but I'm pretty sure it takes about two gallons before the floats move in this airplane.

So I'm pretty sure the new gauge will be accurate when fuel level is(guessing) above 2 gallons or below 23 gallons. Anything outside of that (25 gallon tanks) it will just read empty or full.
Click to expand...

Brian,
I just finished changing my fuel quantity system to an Aerospace Logic FL252 and EI Magnetic Probes. To get the Cessna (or most other) Probes overhauled will cost $300+ each, and the Electronics International Magnetic Probes will never go bad and will always track smoothly with a predictable output and they cost ~$300 new. The FL202 uses your existing resistive probes, which are prone to failure from wear and contamination. Downside to the magnetic probes are that you must run a 5vdc excitation wire out to each sender and in return, they'll send back ~0-5vdc to drive the indicator.

Anyway, my new magnetic probes, adjusted to sit on the bottom of the tank, start floating at a little less than 2 gallons, which is fine with me. If I let myself get that low on gas, accuracy will not be my biggest concern.

They track reliably through the full swing, and I know what my fuel quantity is to the tenth of a gallon at all times. It matches my JPI Fuel Flow readings, and even with these two systems, I still dip my tanks before each flight.

So to the OP, yea, these stock systems are terrible, and it'll cost you a grand in parts to have an accurate system. With fuel exhaustion a primary killer (yea, I know,it only happens to the other, stupid pilots), I feel that $1,000 to help negate that problem was money well spent.
 
Last edited:
JohnAJohnson said:
Brian,
I just finished changing my fuel quantity system to an Aerospace Logic FL252 and EI Magnetic Probes. To get the Cessna (or most other) Probes overhauled will cost $300+ each, and the Electronics International Magnetic Probes will never go bad and will always track smoothly with a predictable output and they cost ~$300 new. The FL202 uses your existing resistive probes, which are prone to failure from wear and contamination. Downside to the magnetic probes are that you must run a 5vdc excitation wire out to each sender and in return, they'll send back ~0-5vdc to drive the indicator.

Anyway, my new magnetic probes, adjusted to sit on the bottom of the tank, start floating at a little less than 2 gallons, which is fine with me. If I let myself get that low on gas, accuracy will not be my biggest concern.

They track reliably through the full swing, and I know what my fuel quantity is to the tenth of a gallon at all times. It matches my JPI Fuel Flow readings, and even with these two systems, I still dip my tanks before each flight.

So to the OP, yea, these stock systems are terrible, and it'll cost you a grand in parts to have an accurate system. With fuel exhaustion a primary killer (yea, I know,it only happens to the other, stupid pilots), I feel that $1,000 to help negate that problem was money well spent.
Click to expand...


You pretty much confirmed everything I've read and came up researching.


I haven't leveled the airplane but did dump 1.5 gallons in one tank and it doesn't raise the float. The Legal unusable of .5 gallon doesn't even make it up it the rib inboard of the float. :rolleyes:
 
My primary fuel gauge is always going to be my eyes looking in the tanks during my pre-flight. I would never rely on any gauge fully. One can reasonable estimate fuel burn during flight and check that the change in the gauges makes sense, but most fuel gauges are going to be a bit off at times (no different than a car).

I would never, for example, flip the master switch on see adequate fuel in the gauge and just go. Also, I'm not always flying on a totally full tank but I'm never going to put myself in a position where I'm thinking "geesh I hope the gauge is correct."
 
rocketflyer84 said:
My primary fuel gauge is always going to be my eyes looking in the tanks during my pre-flight.
Click to expand...
That is good practice, but doesn't work in a lot of airplanes. In my Baron, for example, the caps are at the outboard end of the fuel cell and the dihedral is such that you won't see any visible fuel below about 40-45 gallons (full is 68).
 
Fearless Tower said:
That is good practice, but doesn't work in a lot of airplanes. In my Baron, for example, the caps are at the outboard end of the fuel cell and the dihedral is such that you won't see any visible fuel below about 40-45 gallons (full is 68).
Click to expand...

True... Although in that case I'm still going to want some evidence (other than a gauge) regarding how much fuel is onboard. If for some reason the tank wasn't filled back up I would check the fueling record to see how much was put in the tanks by the truck. If it was filled full and the last flight was 1.5 hrs and now guage says it's down 15 gallons that makes sense (if you burn 10 an hour).

Maybe it's just a personal habit having learned on a Piper Warrior where checking fuel level against the 17 gallon visual tab in the tank is part of preflight (which also made me learn quick that what the guage says and what's in the tanks aren't always completely accurate!), but I just always want confirmation on fuel levels. Taking off without enough fuel is one of the dumbest things a pilot can do and is surely to get one nailed should something happen.
 
JohnAJohnson said:
Brian,
I just finished changing my fuel quantity system to an Aerospace Logic FL252 and EI Magnetic Probes. To get the Cessna (or most other) Probes overhauled will cost $300+ each, and the Electronics International Magnetic Probes will never go bad and will always track smoothly with a predictable output and they cost ~$300 new. The FL202 uses your existing resistive probes, which are prone to failure from wear and contamination. Downside to the magnetic probes are that you must run a 5vdc excitation wire out to each sender and in return, they'll send back ~0-5vdc to drive the indicator.

Anyway, my new magnetic probes, adjusted to sit on the bottom of the tank, start floating at a little less than 2 gallons, which is fine with me. If I let myself get that low on gas, accuracy will not be my biggest concern.

They track reliably through the full swing, and I know what my fuel quantity is to the tenth of a gallon at all times. It matches my JPI Fuel Flow readings, and even with these two systems, I still dip my tanks before each flight.

So to the OP, yea, these stock systems are terrible, and it'll cost you a grand in parts to have an accurate system. With fuel exhaustion a primary killer (yea, I know,it only happens to the other, stupid pilots), I feel that $1,000 to help negate that problem was money well spent.
Click to expand...

I used Aerospace Logic 100 series gauges and new MacFarlane senders. I calibrated the instruments 1 gallon at a time from 3 gallons through 30 and every gallon registered. But that's in level flight attitude in a still hangar. The readings during flight are not so calm or stable. No criticism of AL. Fuel readings in an airplane wing are a difficult task.

I've never heard of EI magnetic senders. My senders are resistive. Simple float arms.
 
Last edited:
Fearless Tower said:
That is good practice, but doesn't work in a lot of airplanes. In my Baron, for example, the caps are at the outboard end of the fuel cell and the dihedral is such that you won't see any visible fuel below about 40-45 gallons (full is 68).
Click to expand...


Doesn't work for most larger aircraft unless they are equipped with a drip stick or something.
 
JeffDG said:
That reg is often mischaracterized as meaning "the guages only need to be accurate when empty" when it actually means that "E" needs to be not empty-empty, but no useable fuel.
Click to expand...

Cessna must be magicians because I don't see how the Cessna 177/B ever met that reg. Unusable fuel is .5 gallons in each tank. It takes over 1.5 gallons to raise the float. How many other aircraft are like that?




 
Last edited:
Fearless Tower said:
I thought his issue was not being able to reach the fuel selector to change tanks?
Click to expand...

That was after he ran the tank dry. This was theorized as happening earlier than expected because the sight gauges didn't read linearly in that aircraft.

My guess was that since he had arranged for a mechanic to work on the fuel selector in the upcoming week that he was specifically trying to burn the tanks down as much as possible.
 
You must log in or register to reply here.
Back
Top