Fuel gauge inaccuracies PA28 Cherokee
Fairly new 1966 Cherokee owner here with the original analog gauges. I’m wondering does anyone else find them inaccurate in flight , I’m finding that my gauges sometimes read a good few gallons more when in flight. If I’m parked with engine running it’s a bit higher usually maybe 2 gallons or more vs engine not running where they’re both pretty much spot on. Is anyone else noticing this? I know they’re to be taken with a pinch of salt it’s just niggling me :D
P.s Right tank sender recently replaced.
Comments
This is why all our CFIs taught us to use a watch and burn rate to “dead reckon,” remaining fuel, rather than the gauges; like you they know how inaccurate they can be!
if you’re parked on the ramp with the engine running and observing the +2 gallons, and then pull the engine back to idle and turn the alternator OFF, what happens? Do the gauges maintain +2, or do they gradually fall to the “engine off,” reading?
just filled up but it seems if I pull the alternator they do drop a little
😀 I find mine most useful as follows:
😀
I mostly use the JPI fuel totalizer and rough calculate duration based on fuel flow. The gauges help me identify if I have a massive fuel leak.
DJ
DJ, that’s too funny. Have you come up with a way to use the angle of attack gauge to detect massive leaks as well? : - ). Bob
I would first see what your alt output is for voltage. Also, what battery voltage is with engine off. On a 66 you could easily have crappy gound or corrosion on connections. Batt voltage should be close to 12.5 and with engine on in the 14.2 range. I would expect the loadmeter to be less than may be 15a with normal equip on. With all the loads off if you still have a good load showing, suspect battery or poor connections some place. Carl
48 yrs A/P IA DAL aircraft inspector. 172N
Battery usually at least 12.5v+ engine running volts around 14v and steady once battery charged, alternator guage once battery charged usually shows no more than two or three amps draw if nothing else is on… nothing seems out of the ordinary with the battery or charging system that I can tell.
Ya, sounds like main system is in good shape. Really only thing left would be to see what if any is the voltage drop at the fuel sender and make sure you have good grounds . If it is something that is way out of wack, you can bend the float arm to tweak the accuracy, even on my cessna gauges, not sure i could tell the difference of 2 gallons. Stock gages just not that accurate. I use a stick to verify actual to gage readings. Surprisingly, my 9000 hr plane gauges are pretty good. If you go to tabs you should be able to get goood idea of indicated vs actual. Bending float levers , doable but more gonna be trial and error. Do a voltage check at the senders some time before you get too involved. Carl
48 yrs A/P IA DAL aircraft inspector. 172N
I have to remind myself sometimes too READ the MANUAL lol.
and manual says 14v to check em. Way i read, you better than book! CArl
48 yrs A/P IA DAL aircraft inspector. 172N
Lol that pic pretty much explains it then 😂
When I get an AOA, I'll see if it can be calibrated to get an in-flight weight vs predicted decrease due to fuel burn. 😀
Planewrench, that is truely eye opening. Can you please post the aircraft model and year for this info?
I always thought fuel gauges in aircraft were only a little better than a wild guess. Mine read full when full, and empty when empty. When both are at half, one reads one quarter and the other reads three quarters. I replaced a gauge once with new while we had a tank off and thought that would fix it. Nope, the older one was actually better. We have looked at grounds and found no issues. If the float rod was custom bent to match the tank's indications I would have it made, but it wasn't worth the trouble of removing everything to do that.
Jim
Mike, the information i quoted was from the Piper MM covering pa28 140 all the way thru the 28r-200.
Carl
48 yrs A/P IA DAL aircraft inspector. 172N
All:
If you remove the Piper sending units, there is a procedure to bench calibrate them. Check the maintenance manual for your model.
Before calibrating, I wiped down the rheostat with lacquer thinner. A lot of crud was removed. The factory sending units are not perfect (never are), but generally give you enough warning that it's time to descend and top off.
As has been mentioned numerous times already, it's far better to monitor remaining fuel by using a clock and the burn rate (not including electronic fuel totalizers).
I've owned my plane 25 yrs, so I know it well. When I pull up to the pumps, I can usually predict within 1-2 gallons how much fuel the plane needs.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
Makes one wonder what the tolerance is on the leaning instrumentation, engine instrumentation, and the airspeed indicator, all of which can affect calculated fuel burn! Never the less, I usually leave an hour reserve which works well with a bio break 😀
Way back when I took Philosophy 101 we spent (wasted?) an entire semester debating and arguing over proofs of the existence of God. There was the Ontological argument, the Cosmological argument, and a whole bunch of others I can neither remember, nor spell.
Well, Mike you just reminded me there's a far more plausible, contemporary proof: The Grand Bladder argument. It's simply this: "God sized the human bladder so that GA pilots are FAR more likely to end up in the restroom, than in the middle of a lake, swimming for shore."
: - )
Seneca;
So true!! I am often asked "How long can you fly in your plane without stopping?"
I know in my head that I can fly from Chicago to Atlanta on one tank, but my stock answer has become "As long as my passenger with the smallest bladder can hold out."
And that's why I generally flight plan x-country trips with a stop every 2.5 to 3 hrs.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
One of my fuel gauges has always read 1/4 tank too low. Would the tank have to be removed or could the arm be bent without removal? I have already discussed putting a resistor to the gauge with my IA as a way to fix, but he says can't do that. Certainly looks like that would work though.
Ya, that far off worth pulling the tank to see whats going on with the float. Make sure the connections are good at the float and you have good grounds on the side that is bad. Using a mirror, you can see the float in the tank, make sure its all intact. I have had good luck "testing" the sender by bending a long piece of coat hanger or welding rod in order to manipulate the lever up and down in the tank to check ops. Might be worth a try too. If you take the tank out.. save time and money for the shop by YOU loosening all the tank screws. Thats the biggest time user. If the screws are all shot, get new ones before you start.
Carl
And agree, no adding resistors to make it work. That would technically be a major alteration. LOLl
48 yrs A/P IA DAL aircraft inspector. 172N
This has got me to thinking about how I fly. My Arrow has the 50 gallon tank and just from years of aiming Arrows I know 4 hours puts me real close to my VFR mins. I learned this when I was younger now that I am older I can’t last 4 hours without a stop.
Now having just flown from Central Ohio to Sun N Blister down in Florida I broke the legs up to 3.5 and just under 3 hours legs and was very diligent to switch tanks right on the hour and with the new electronic toy I flew at the fuel flow on the flight plan. I think I needed 33 gallons and fuel management had the total fuel put in each wing to less than a 5 gallon split.
As I recall my gauges showed a little more of a difference. The fullest tank showed right at half and the emptiest tank, right tank showed just above 5 gallons. I think maybe my fullest tank was generous and maybe my lowest tank was reading a bit low. I was more impressed that ForeFlight and I managed to fly the flight plan and use real close to the planned fuel burn and I did not worry about what the gauges said but now I will watch this more closely. I was just more pleased I duplicated ForeFlight fuel burn and times.
On cross country flights as long as I follow my flight plan and change tanks on time I should have legal mins when the time en route is reached. So if I encounter a giant headwind when I reach my planned time en route I will know exactly my fuel remaining. Please excuse my musings, I did this professionally for 20 years as an aircraft dispatcher. Many a time I told the pilot just fly the plan you will have the gas, I had to tell myself now. I must remember fuel is a function of time not distance in airplanes and I must use the red lever to decrease my fuel burn to fly the plan.
Now that I think about it, my gas gauges don’t agree. I have some time and I have 6, six gallon gas cans decorating my garage so I may record what every 3 gallons looks like on my gauges. Everyone needs a hobby mine will be lifting gas cans, once I get proper motivation.
1973 Arrow II factory AC removed
G5’S, G275, GNX375 Still can get lost.