Wing Fuel Dial

[flyfast]

My right side wing mounted fuel gauge decided to fly the coop. Does anyone know where I can get one? 

[KSMooniac]

You can only get them through a Mooney Service Center, so call your favorite and cross your fingers.  

[Ragsf15e]

2 hours ago, flyfast said:

My right side wing mounted fuel gauge decided to fly the coop. Does anyone know where I can get one? 

There’s a thread around here where @dkkim73 did an awesome job with an ots sensor from the same company that made the Mooney ones.  His look real nice.  I can’t find the thread but I’ll bet he’ll help us out.

[dkkim73]

Ah, you have the Acclaim as well. As you might know, the marking are all different. I detailed my issues in this thread, linking here to the post where I described my improvised solution (starting with available dials). It's been working pretty well: 

 

 

 

@Ragsf15e thanks for the kind words. As chief engineer of Ghetto Aviation, I am flattered...

 

[Ragsf15e]

1 hour ago, dkkim73 said:

Ah, you have the Acclaim as well. As you might know, the marking are all different. I detailed my issues in this thread, linking here to the post where I described my improvised solution (starting with available dials). It's been working pretty well: 

 

 

 

@Ragsf15e thanks for the kind words. As chief engineer of Ghetto Aviation, I am flattered...

 

I now have a 252 with the same dials. They seem pretty necessary since you can’t easily see down there and measure the fuel.  I just hope mine are glued in real good!

[Z W]

6 hours ago, Ragsf15e said:

I now have a 252 with the same dials. They seem pretty necessary since you can’t easily see down there and measure the fuel.  I just hope mine are glued in real good!

They're kind of nice to have, but I wouldn't say "necessary." Mine are pretty accurate until they get below about 12 gallons, then they suddenly start reading zero. Really bothered me at first. Still bothers me a little bit, even though I know.

Useful mostly for seeing if the fuel guy got to you without having to power on the plane and check the dash gauges or physically look in the tank. I don't find them reliable as an in-flight cross-check when it matters. Your experience may vary.

[Ragsf15e]

3 hours ago, Z W said:

They're kind of nice to have, but I wouldn't say "necessary." Mine are pretty accurate until they get below about 12 gallons, then they suddenly start reading zero. Really bothered me at first. Still bothers me a little bit, even though I know.

Useful mostly for seeing if the fuel guy got to you without having to power on the plane and check the dash gauges or physically look in the tank. I don't find them reliable as an in-flight cross-check when it matters. Your experience may vary.

Ok, humor my dumb question since I’m new to my 252… how do you get a good look in the tanks with that metal flapper in the way?  And can you dip them or see a tab?  Id really like to know exactly how much fuel I have (and I have cies senders with a g3x, so it should be good), but I haven’t been able to really verify it yet.  In my F, i could see the tab and verify 25 gallons.  In this one, I have Monroy tanks, so if I get more than ~30gallons in the mains, some will feed into the outbound tanks and then nothing reads right?

[Pinecone]

You can just push the flap with your finger to look in.

You can dip the tanks also.  Just push the flap down, inside measuring device and measure.  I did an article for Mooney Flyer in fall 2022 about how to calibrate your dipstick and some options.   My favorite now is the short Universal Fuel Hawk.

https://www.aircraftspruce.com/catalog/pspages/fuelhawkuniv11.php

Or, if you want a more precise reading the Fuel Stick.  With the fuel stick, if you send your calibration numbers and they will send you a file that is customized to YOUR plane and reads out in Gallons.

https://www.sportys.com/fuelstik.html?utm_source=google&utm_medium=cpc&utm_campaign=&creative={AdId}&device=c&matchtype=&gad_source=1&gclid=EAIaIQobChMIlsuBqtS0iwMVq1xHAR3swTn6EAQYAiABEgIbffD_BwE

[Z W]

3 hours ago, Ragsf15e said:

Ok, humor my dumb question since I’m new to my 252… how do you get a good look in the tanks with that metal flapper in the way?  And can you dip them or see a tab?  Id really like to know exactly how much fuel I have (and I have cies senders with a g3x, so it should be good), but I haven’t been able to really verify it yet.  In my F, i could see the tab and verify 25 gallons.  In this one, I have Monroy tanks, so if I get more than ~30gallons in the mains, some will feed into the outbound tanks and then nothing reads right?

This is, in my opinion, one of the weaknesses of the 252, or likely any Mooney with long range tanks. It's very difficult to know with precision how much fuel you have on board unless you always do the fueling yourself, which I have not found to be practical. I usually fly around knowing within 10 gallons +/- what is in the tanks. I compensate by planning to land with 2+ hours of fuel on board, which is easy to do because of the plane's efficiency.

The problem is - you ask the FBO to "top the inboard tanks" which should be 75 gallons on board. In reality, they sometimes short you by as much as 5 gallons per side, depending on how patient the line guy is in topping you up. And you can't tell how much you were shorted by looking in the tanks, because by the time you get back to the plane, the fuel has flowed out into the outboard tanks and you can see those are 1/3 full and the mains are 2/3 full. You get in the plane, and set the fuel totalizer to 75 gallons, because that's a pretty good guess, but often you're really at 65-75. Sometimes I adjust the totalizer setting based on the fuel receipt or by what I see on the visual check.

Then you fly for 3 hours, or about 36 gallons, land, and ask the FBO to "top the mains" again. Same problem repeats. You will rarely fully top both the inboards and outboards, because if you do, most planes are over gross or near it with just the pilot and a small bag. So you're always doing the dance between fuel orders, looking in the tank, fuel totalizer, and looking at the fuel receipts. Looking at the wing gauges can kind of help but not really.

It's not really a problem because 75 gallons in the inboards is about 5.5 hours of endurance which is way longer than I like to fly. But on one or two occasions, I've ended up fighting headwinds, extending my planned flight to 4.25 hours, and worrying about the fuel levels because the FBO only filled me with 30 gallons when it should have been more like 40. If I know I'm doing a 4-hour leg, I will put 10 gallons or so into the long range tanks if possible and try to take off with 85 gallons on board. Even better yet, if I fuel myself at a self-serve pump, I can make sure I get a good top off and it's much less of an issue, but the way I fly that's not always an option.

The only other solution is to do like @Pinecone has done and create a custom spreadsheet with dipstick measurements for each tank. To truly maximize your range I think that's required. But I don't like pushing range or staring at empty fuel gauges, so I just land with 25+ gallons on board. If I ever have to have 4 adults on board, which is rare, I try to take off with 50 gallons and limit my flight to 2.5 hours max.

[Ragsf15e]

5 hours ago, Z W said:

This is, in my opinion, one of the weaknesses of the 252, or likely any Mooney with long range tanks. It's very difficult to know with precision how much fuel you have on board unless you always do the fueling yourself, which I have not found to be practical. I usually fly around knowing within 10 gallons +/- what is in the tanks. I compensate by planning to land with 2+ hours of fuel on board, which is easy to do because of the plane's efficiency.

The problem is - you ask the FBO to "top the inboard tanks" which should be 75 gallons on board. In reality, they sometimes short you by as much as 5 gallons per side, depending on how patient the line guy is in topping you up. And you can't tell how much you were shorted by looking in the tanks, because by the time you get back to the plane, the fuel has flowed out into the outboard tanks and you can see those are 1/3 full and the mains are 2/3 full. You get in the plane, and set the fuel totalizer to 75 gallons, because that's a pretty good guess, but often you're really at 65-75. Sometimes I adjust the totalizer setting based on the fuel receipt or by what I see on the visual check.

Then you fly for 3 hours, or about 36 gallons, land, and ask the FBO to "top the mains" again. Same problem repeats. You will rarely fully top both the inboards and outboards, because if you do, most planes are over gross or near it with just the pilot and a small bag. So you're always doing the dance between fuel orders, looking in the tank, fuel totalizer, and looking at the fuel receipts. Looking at the wing gauges can kind of help but not really.

It's not really a problem because 75 gallons in the inboards is about 5.5 hours of endurance which is way longer than I like to fly. But on one or two occasions, I've ended up fighting headwinds, extending my planned flight to 4.25 hours, and worrying about the fuel levels because the FBO only filled me with 30 gallons when it should have been more like 40. If I know I'm doing a 4-hour leg, I will put 10 gallons or so into the long range tanks if possible and try to take off with 85 gallons on board. Even better yet, if I fuel myself at a self-serve pump, I can make sure I get a good top off and it's much less of an issue, but the way I fly that's not always an option.

The only other solution is to do like @Pinecone has done and create a custom spreadsheet with dipstick measurements for each tank. To truly maximize your range I think that's required. But I don't like pushing range or staring at empty fuel gauges, so I just land with 25+ gallons on board. If I ever have to have 4 adults on board, which is rare, I try to take off with 50 gallons and limit my flight to 2.5 hours max.

Very helpful, thanks.  I also found @Pinecones thread on his fuel sticks.  Both techniques are helpful.  I usually fly with 4 people (2 kids) and we often fly 500+nm, so the lbs are important.  Having the extra gw of the Encore conversion helps, but I don’t want to carry around too much extra (or short myself).

[Pinecone]

The other option is the Cies senders.  When calibrated to a good fuel gauge, they are accurate to the gallon. But a LOT more cost than a dipstick of some sort.

[dkkim73]

It would be nice to have better electronic senders. Lower down on the list of spend priorities, but still. 

I think someone above mentioned they didn't have great experience with the mechanical wing gauges. I've found them very useful. My experience (also foretold by my transition instructor) is that accuracy goes: 

1. Totalizer/FF meter and keeping track of burn -isbetterthan- 2. Wing gauges -isbetterthan- 3.  Electronic senders that feed G1000. 

Current practice is to watch burning and predictions (FPL on G1000) and look at the wing gauges as part of my periodic cruise checks. I think they're a great safety feature and @PT20J's tip of putting clear tape over them has worked well to prevent them from debarking prior to destination. 

 

 

[NickG]

7 hours ago, Pinecone said:

The other option is the Cies senders.  When calibrated to a good fuel gauge, they are accurate to the gallon. But a LOT more cost than a dipstick of some sort.

I have Cies senders. They are very accurate. Combined with my G3X and the engine data that automatically downloads to my ipad, I can see the exact fuel quantity I have at shutdown. While I love wing gauges for their convenience, I don't need them. 

[Ragsf15e]

On 2/10/2025 at 5:35 PM, NickG said:

I have Cies senders. They are very accurate. Combined with my G3X and the engine data that automatically downloads to my ipad, I can see the exact fuel quantity I have at shutdown. While I love wing gauges for their convenience, I don't need them. 

The hard thing is with the Monroy tanks.  Since they feed back and forth to the mains, it’s harder to just look in and verify what your gages and totalizer say.  I have cies and g3x as well, but it’s a little disconcerting until you’ve gone through the exercise @Pinecone did to verify exactly what he had, where it was, and how to verify (measure) it.

[Z W]

The dash gauges on my G500TXi are very accurate once you get below about 25 gallons total on that side. It's just when you are over 25 gallons and some of that fuel is out in the Monroy extended tank, the gauge is still going to read 25 gallons, even though you have more. The wing gauge will do the same.

If starting out after a fuel stop where the inboard tanks were topped (37.5 gallons per side in theory), the gauges will read full, then quickly drop to about 25 gallons as the fuel flows out into the outboards, then stay at 25 gallons until you get below that, then become accurate again until 0.

If starting out quickly after fully topping both inboard and outboard tanks (52.5 gallons per side, rarely done), the gauges will sit pegged at full until you reach somewhere around 37 gallons of actual fuel, then the gauges will quickly drop to about 25 (inaccurate) and stay there until you reach 25 gallons of actual fuel, then be accurate again until 0.

The gauge system is reliable but inaccurate and can be confusing.  You have to think about it and understand how it works. If you don't, you may be alarmed as the gauges quickly drop and think you have a fuel leak somewhere, or that they're frozen in place when they stop moving. And, as I said before, my wing gauges quickly drop from 10 to 0 as well and are not reliable at those levels. 

If the plane were not so efficient, making it easy to just carry extra fuel, I think this would be more of a problem than it really is.