How full is full on your fuel tanks?

[JCD]

My M20J 201 holds 32 gallons per side in her tanks. There are tabs in the tanks that at the bottom of the tabs, on level ground, are the 25 gallons of fuel remaining.

 

My question is what is full 32 gallons? Is it to the top so that when you put the cap in it overflows? Is there a marking on the tab that shows full? How are you suppose to know you in fact have the full 32 gallons in each tank?

 

Any expertise on this is greatly appreciated.

 

 

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[kortopates]

Full is at the base of the pipe or fill tube. Above the base of the fill tube is for expansion. But yes you can keep filling above "Full" but you should be at rated capacity at the base. You should empty each tank and actually measure it as many Mooney owners have done since many  have found they have less than than rated capacity. One reason for this is if sealant was applied to vent holes in the top of the rib, then the inside bay will not be able to vent the air and won't fill on its own. Before you count on gallons you may or may not have its a good idea to measure your capacity and calibrate your own dip stick for measuring partially filled tanks. It will also ensure you have an accurate weight for any fill level you decide to use. if you have the little fuel gauges on the top of the tank you can also verify their accuracy. They are usually pretty good.

[carusoam]

Added detail...  the POH usually has some of these details.  A modern POH has fuel level covered in several places.  Proper decals. Temperature vs. fuel density.  Procedures for filling.  Use of 'dry gas'.  Annuciator panel and how to initiate the fuel low level warning system.  The instrument panel also has some detail as does the fuel tank selector valve.

The part You will find most amusing.  New owners test the accuracy of their fuel level system.  They also develop a way to know how much fuel is in the tank when it is partially filled.  Search on sticking the tank.

There is a fair amount of level sensor challenges and solutions to read about.

Check the calibration of your Fuel Flow system.  Compare the fuel used numbers to the reality of what is left in the tank or how fuel it takes to refill.

Does your panel have a fully integrated JPI?  There are some new digital fuel level sensors that would go good with that...

When you are done, compare your paperwork and procedures to reality.  It would be crummy to find out something isn't right the hard way.  Trust but verify is the only way to know before you go... 

PP thoughts only...

Best regards,

-a-

Edited February 8, 2017 by carusoam

[Bob - S50]

Last time we calibrated our digital fuel gauge, 32 gallons put the level just over the lower lip of the fill port.

If you trust your 25 gallons tabs, fill to that point and then see if you can put another 7 gallons in.  If so, see where the level is.  If not, you'll know how much you can get in the wing.  Either that or the 25 gallon tab is inaccurate.

Either way, if you are worried about 2 gallons of gas, you are pushing the envelope anyway.  I plan to land with 10+ gallons.  If I was off by 2 gallons/side, I'd still be landing with 6.

But, as said by others, drain the tank, then meter in fuel to see where 25 and 32 gallons really are.  I know that if the wing is just barely wet below the fill port, there are 7 gallons in that tank.

[peevee]

with the monroy tanks, god only knows.

[201er]

4 hours ago, peevee said:

with the monroy tanks, god only knows.

Are you calling Jose god or are you implying that even he doesn't know? Which is it?

[Hank]

I generally fill to 1/2" below the top of the opening, so there is room for expansion in the sun, if I am not departing immediately. For max capacity takeoff, I fill 'em right to the top at the back of the cap, but can't imagine that the ~1/2 gallon per side will make much of a difference. Although I have noticed that when traveling, the latter is always employed by the FBOs where I stop . . .

[mikeyhaley]

I just ran my right tank out of fuel coming back from Phoenix earlier today. I wanted to make sure where the "full" mark is as well. I've done it before and can't find where I wrote it down, and of course, I'm second guessing myself. I have an M20K and the capacity is 38.5 in each side with 35 usable. For some reason I remember I could only fit another 33 in each side after the tank "runs out". (2 gallons short of what the POH says) It seems the last 3 gallons or so take forever since you have to pump it very slowly. I'll report back when I fill it up. Stayed tuned!

[mikeyhaley]

I also wanted to see what the fuel gauge reads when the tank is out of usable fuel. Looks like the left edge of the needle is right at the right edge of the last white part. It clearly does not read properly. The needle is far from the "red" of empty and was at that spot for the last 10-15 minutes before it finally sputtered and ran out of fuel.

 

Edited February 10, 2017 by mikeyhaley
Added image

[JCD]

I generally fill to 1/2" below the top of the opening, so there is room for expansion in the sun, if I am not departing immediately. For max capacity takeoff, I fill 'em right to the top at the back of the cap, but can't imagine that the ~1/2 gallon per side will make much of a difference. Although I have noticed that when traveling, the latter is always employed by the FBOs where I stop . . .

Yes except for the Henderson Airport (KHND) they filled my tanks to the brim then shoved the caps on and then it got warm. Fuel expanded and stained my wing over a year ago. Although it has faded a little there is still a blue stain on my paint. Worst pRt was they put the caps on crooked and it came a monsoon and I spent an hour draining water from my tanks. Was not fun!


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[JCD]

I just ran my right tank out of fuel coming back from Phoenix earlier today. I wanted to make sure where the "full" mark is as well. I've done it before and can't find where I wrote it down, and of course, I'm second guessing myself. I have an M20K and the capacity is 38.5 in each side with 35 usable. For some reason I remember I could only fit another 33 in each side after the tank "runs out". (2 gallons short of what the POH says) It seems the last 3 gallons or so take forever since you have to pump it very slowly. I'll report back when I fill it up. Stayed tuned!

Yes very interested in your results. How do you run your tanks dry? Do you fly it until the engine stops?


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[JCD]

I also wanted to see what the fuel gauge reads when the tank is out of usable fuel. Looks like the left edge of the needle is right at the right edge of the last white part. It clearly does not read properly. The needle is far from the "red" of empty and was at that spot for the last 10-15 minutes before it finally sputtered and ran out of fuel.
 

Sputtered? I am not that gutsy.


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[Hank]

22 minutes ago, JCD said:

Sputtered? I am not that gutsy.
 

 

That's the most accurate way to know that your tank is dry. If you drain it on the ground, the angle of the wing is different, and by removing the drain, you are creating new artificial low spot that you won't be able to reach with the plug in.

Just be ready, make sure there is fuel in the other tank and that the switching valve moves freely. Watch the fuel pressure, it may become unsteady. The engine may sputter and cough a couple of times, it may just cut off  (mine has done both . . . ). Retard the throttle a little bit, switch the fuel and she should fire right back up--so reset the power and motor on. Do try to have this happen with enough fuel to reach a good airport or your home field, where you can  shut down a day see what's in the tank a day how much it takes to fill it back up. 

If you're gonna do do this, take the time to make a dip stick for yourself. Add fuel in 1 or 2 gallon increments, dip the tank with a paint stir stick and make a mark. This will let you dip the tanks with confidence and know the amount of usable fuel in them very accurately. 

[aaronk25]

I run a tank dry in flight as a standard practice on long endurance flights. 33.3 gallons in the J with 32 usable in most flight attitudes. Always know when it's in the last .5 gallon as the slightest nose down attitude will cause it to sputter as fuel pickup is in aft part of tank.

On a long flight if going to land with 1 hour fuel in reserve (good weather, daytime) it's better to have it all in one tank instead of 5gallons a side sloshing around. Also 5gallons is not readable on the wing sight gauges but 10gallons is so it's another 3rd check of how much fuel is on board with the 1st being the electric gauges, 2nd bring fuel totalizer and 3rd cross check against the wing sight gauges.


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[mikeyhaley]

12 hours ago, JCD said:

 

Yes very interested in your results. How do you run your tanks dry? Do you fly it until the engine stops?


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Oh it sputters! Not gonna lie, I was nervous ...er um OK very very nervous! The first time I tried it on my way back from KADH. I actually chickened out the first time and decided the needle was low enough! At that time I only had my PP for 3 months. I was definitely erroring on the side of caution. But after I was way more comfortable flying, I ran it dry. The engine sputters a little then you just switch it to the other tank and away ya go. (P.S. Don't do it with your nervous GF in the co-pilot seat. oops!) If you have an engine monitor, you will see the temps to start fluctuating about 6-8 seconds before the engine sputters. Now... that being said, make sure you turn the boost pump ON if you previously ran the other tank dry. You may crap your pants a little when you switch tanks and away you DON'T go. Glad I was quick on my reaction and turned the boost pump on the first time I ran both tanks dry. (Obviously not at the same time, but back to back flights) Good news is I was over the desert at 12k so had plenty of time and not a big deal.

[aaronk25]

I wonder if it should be part of private pilot training to turn the fuel selector off to give the experience of what a engine failure feels like and respond to it calmly making sure the pilot knows it's going to happen. Also would kill the fear of running a tank out.


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