LOW FUEL L-R warning light

[turbotrk]

Hi, I own by less than one year an M20K 252 TSE and I have been doing several tests on the fuel flow meter and fuel televels. What I have found is actually the LOW FUEL L-R coming out earlier than specified in the POH, at least I suppose so. The light should come on when there is left 2.5 to 3 GAL usable fuel but during refill I noticed that to have full tanks I needed 5 gallons less. That means that in my aircraft the light comes on when there is less than 7.5-8 gallons. Also the FF indicator seems to agree perfectly with the amount of fuel burned and the that needed to refill to full. The problem is that 7.5 on both tanks is still one our flying time and could make the difference when you have to make planning, but I have to be 100% sure that this is true as flying with that light on does not make me feel confortable and I have not tryed to see after how long it starts not to supply fuel anymore.

Does anybody who has the same plane have the same problem?

[Jeff_S]

My fuel warning lights always seem to come on with 8 gallons remaining...at least this was true in the J. I haven't tested it in the Ovation, but I seem to recall that's what the POH says. I'll have to double check. But are you sure your POH says it would come on with only 2.5-3 gallons left? That seems awfully low...almost like that's the unusable fuel in the tank.  You might want to check that again.

 

And then...

 

Well, just checked the POH and here's what mine says:

 

"RED light indicates 6 to 8 gals. (23 to 30.3 liters) S/N 29-0170 thru 29-TBA of usable fuel remain in the respective tanks. Switch to fuller tank."

[carusoam]

Fuel levels and warning lights are not as accurate or as reliable as FF can be.

Both require proper testing (as a new owner ) to make sure they match the POH values.

To get the accuracy, FF has some challenges as well. The K factor is adjustable. Don't forget to reset the total to zero when refilling.

Total fuel volume is often a question of the method used to fill up. How level is the ground? To how high up the fill neck is proper? How much air gets trapped?

With experience AND these two systems, a pilot can accurately calculate the usable fuel left in the tank.

The tie-breaker is the wing mounted fuel gauges on the wing, use caution, these are calibrated for attitude on the ground.

It may take several flights repeating the procedure over and over to be comfortable.

Trust, but verify!

If you don't prove it to yourself first, you won't be able to use it comfortably...

Welcome aboard,

-a-

[turbotrk]

This is what is in the POH. Warning light is connected to televel, so not really reliable on my advise.

As I stated before it says that light comes on when there is less than 2-1/2 , 3 gallon of usable fuel in the respective tanks.

Fuel flow is adjustable as I have a Shadin Miniflow L and I can change it with any K factor but at the moment 85000 in accordance with the STC seems to be working pretty well.

[orionflt]

so what your saying is that the light comes on with 6.5-7 gallons of usable fuel remaining per side.....I do not see that as a problem, you know that the numbers are and honestly they are in line with your IFR reserve numbers.

 

Brian 

[Bob - S50]

Remember that indications are supposed to be in level flight, not on the ground.  To test for accuracy you'll need to put the airplane into a level flight attitude first.  For our J we had to put the plane on jacks because you really have to raise the tail a LOT to get to level flight attitude.  For the J, level flight is measured at the battery access door.  Check your POH for correct procedures (weight and balance section).

 

Once you have the plane in the proper attitude and the tanks drained, add the unusable fuel.  Then you can start measuring fuel into the tank.  I used a gallon milk jug that I washed thoroughly and calibrated with water using my wife's kitchen measuring cup.  Add fuel until the light goes out.

 

Bob

[turbotrk]

Good idea, I am going to try that, it's better to find fisically when the lights come on rather than calculating it and rely on numbers. Of course if it is more I am on the safe side but on some occasions, like bad weather diverting, it can make the difference on deciding where to go.

[carqwik]

If your low fuel light(s) come on in flight, it means one of two things... "it's time to land this sucker" or "switch tanks you dummy!"

[Awful_Charlie]

I'm a bit anal about fuel indications, and spent the time calibrating it so I know exactly where I am from what I can get. Hopefully that means the loss of one system gives me other options.

 

To start with, I record all fuel that goes in, and the Shadin 'Used' and 'Remaining' after each flight. This means I can get the Shadin (and as it happens, the EDM, which is fed from the same transducer) to within 2%. There's not much point IMO trying to get it closer, as fuel dispensing equipment is allowed (in the EU anyway, not sure about the US) a +1% -0.5% tolerance, and the transducer is measuring volume (not weight) and of course the density changes with temperature, so you can't easily guarantee what you put in is exactly what you are going to have to burn!.

 

Having got a good fuel flow figure, I can then run a tank dry in flight. This is also a handy point to note if the internal gauge is accurate at the empty point (adjustment method in the MM) By recording the Shadin figure when the low fuel light comes on, and again when the engine starts to surge, I can calculate the fuel remaining when the light first comes on. (adjustment for this figure is in the MM)

On the ground, I then fill the tank to each of the marks on the wing gauge and record how much goes in for each graduation. I now have a figure for each mark when the aircraft is in ground attitude. I can also check the internal gauge 'Full' indication (again, adjustment method in the MM) as soon as airborne.

 

When I next go flying, I can record (from the Shadin) the fuel burnt at each graduation on the internal gauge, and also the wing indicator. (note this might require a bit of a table, as a massive fuel imbalance isn't pleasant to fly with, so also need to record the Shadin figures at each tank change point) Now I have a complete set of figures for one tank - then it's time to repeat for the other side. (I don't fancy running both sides dry in flight!)

 

Of course, things change, sometimes planned and sometimes not, so I try to make a habit of running a tank dry at least once a year to make sure I'm not placing trust in things that don't warrant it. By comparing what was with what's now, I can see if things are changing, and decide if that warrants attention.

 

I did very few of these flights with the sole purpose of calibrating the fuel, just continuous recording of what happened when, and then worked it out from the comfort of home. Of course, like the OP, I buy and order fuel in litres, yes all my indications are in USG, so there's a conversion factor to put in too. I keep a crib sheet on my kneeboard to work out the 'Fuel Added' figure for the Shadin when not filling up.

 

FWIW. my left warning comes on with 1.9USG remaining, the right with 2.6, so at about 10 mins to go for each at my fuel flows. I'd like to knock them up a bit, so more like 20-30 mins a side, it's on the 'To Do' list, as the MM specifies between 6 and 9 as the trigger point which would fit

[N601RX]

Although with the JPI 900 I finally have a digital fuel level readout that has been calibrated and appears to work well, I still have more trust in the fuel flow transducer. I no longer switch tanks every 30 minutes as I was originally trained to do, I just switch them every 10 gallons. That makes it very easy for me to keep up with how much fuel is in left in each tanks and it accurately accounts for fuel used during climb or any other flight condition.

[LANCECASPER]

My hope is to never see see either of those lights and never be part of the most preventable accident in aviation - fuel starvation.

[ovation0219]

Those lights are adjustable my AI flew tank down to engine sputter switched tanks landed added 9 gallons and adjusted light to that amount with plane leveled as it would be in flight. they both work perfectly every time.

[1964-M20E]

My recent trip had me landing with the least amount of fuel so far and that was 1 hour of flying time and that was close enough to empty for me.  I felt confident having the fuel flow meter and knowing how much I've used and how much was left.  With out the fuel flow I would have landed and fueled up at some point just to be sure.  Keeping track of flight times is the backup plan.

 

 

With the 54 gallon bladders I burn 10 off one tank and then 20 or more from the opposite tank or until I'm about 15 minuets from my destination then I select the fullest tank for landing.

[Danb]

Charlie is there a hazard in running a tank dry such as getting dirt in the injectors etc..I have no clue just asking for my knowledge...

[Awful_Charlie]

I guess there might be a very slight chance, but running a tank low exposes you to as much risk.

 

The tank pickup is about 1/2 or 3/8" diameter, and the exposed end is tubular gauze about 2" long. it sits 1/4" or 1/2" above the bottom surface of the tank. Heavy material will sit on the bottom of the tank and get ignored by the pickup. and hopefully migrate towards the drain when you pull it out when sampling. Floating 'scum' if it fits through the gauze could potentially get as far as the gascolator where it should be filtered out. If it gets past there, there is another filter in the injector assembly, which I have a suspicion is actually coarser that the gascolator.

 

Of course, if you are not careful what you put in your tank in the first place, then you make your chances of all sorts of failures higher!

[Piloto]

Un useable fuel as per POH is during an attitude that can cause fuel to un port such as a steep side slip. In normal level flight the un useable fuel amount is much lower. Keep in mind that the warning light does not know if you are in a climb or side slip or in strong headwinds or your other tank is empty.

 

José

[N201MKTurbo]

I would suspect the inlet filter on the RSA-5 won't let anything through that won't pass through the system.

[Cruiser]

I tried confirming the Low Fuel Alert by running on one tank till the light came on to check it. It got down to 3 gallons on the digital gauge and was still running smooth before I chickened out and switched to the other tank with plenty of fuel in it. When I made my turn to enter the pattern, the low fuel light came on and stayed on for that tank.

 

I guess that really doesn't tell me anything, but my plan would be to keep enough fuel in one tank to get me to my destination and then run on the the other tank till the low fuel light comes on.

[unicom]

Hi All,

Since I had installed Monroy Long Range Fuel Tanks last year, I wanted to measure precisely what was the amount of fuel my M20J could carry. I understand this amount may vary slightly from one aircraft to the other.

After reading the POH, I found out the low fuel light would come on with a remaining quantity of 2.5 to 3 gallons. Then, completing the refill of the tank, that would give me a good idea of the usable amount of fuel in my wings. That was the plan...

With my left fuel gauge now reading 0 at 5500', I was nervously waiting for the left low fuel light alarm to come on...when my engine suddenly decided to run rough due to fuel starvation !!!

That is exactly at that moment that the low fuel alarm decided to finally illuminate...just a bit late  !!!

I understand the Low Fuel Alarm sensor can be adjusted. Anyone could please explain what is the procedure ? It is not that I do not trust my mechanic, but I found it generally saves a lot of time with prior advice from my fellow mooney pilots.

Cheers,

Philippe

1980 M20J - FGPHR

[turbotrk]

2 hours ago, unicom said:

Here is the  Hi All,

Since I had installed Monroy Long Range Fuel Tanks last year, I wanted to measure precisely what was the amount of fuel my M20J could carry. I understand this amount may vary slightly from one aircraft to the other.

After reading the POH, I found out the low fuel light would come on with a remaining quantity of 2.5 to 3 gallons. Then, completing the refill of the tank, that would give me a good idea of the usable amount of fuel in my wings. That was the plan...

With my left fuel gauge now reading 0 at 5500', I was nervously waiting for the left low fuel light alarm to come on...when my engine suddenly decided to run rough due to fuel starvation !!!

That is exactly at that moment that the low fuel alarm decided to finally illuminate...just a bit late  !!!

I understand the Low Fuel Alarm sensor can be adjusted. Anyone could please explain what is the procedure ? It is not that I do not trust my mechanic, but I found it generally saves a lot of time with prior advice from my fellow mooney pilots.

Cheers,

Philippe

1980 M20J - FGPHR

Here is the procedure:

[StevenL757]

On October 13, 2014 at 3:00 PM, N601RX said:

Although with the JPI 900 I finally have a digital fuel level readout that has been calibrated and appears to work well, I still have more trust in the fuel flow transducer. I no longer switch tanks every 30 minutes as I was originally trained to do, I just switch them every 10 gallons. That makes it very easy for me to keep up with how much fuel is in left in each tanks and it accurately accounts for fuel used during climb or any other flight condition.

Just curious...whose digital senders do you have?  Did you work with CIES in Oregon?

[Yetti]

I think gasoline will melt a milk jug after a while.  At least the older ones it would.  The fuel servo screen should be checked at annual and it is very fine screen

[M20S Driver]

Don Maxwell says not to dry a tank in a Mooney...  Never.

His reasoning is that the "O" rings in the fuel selector valve may not be perfect and leak air from the empty tank side causing compromised fuel flow between the mechanical pump and fuller tank.   

My low fuel light comes on at about 7.5 gal and I make sure the other tank is at 12 gal or more at destination...  This is my personal absolute minimum.

[unicom]

6 hours ago, turbotrk said:

Here is the procedure:

 

Hi Turbotrk

Thank you so much for this very quick response.

I will try that with my mechanic and let you know the result.

Cheers,

Philippe

[rbridges]

that reminds me of my Garmin GPS with traffic alert for the car.  My wife and I laugh about how it gives a heavy traffic warning about the time you've already reached it.