M20F Fuel Transmitter Issue

[TonyPynes]

Just had my Mooney's annual completed. It was my first one and it went well and very happy with the experience. One issue that is still being worked out is the fuel level transmitters and gage calibration. Original issue was left tank gage took a few minutes to come alive each time I flew, which is not a problem really but the other was the left tank also recently started showing another problem, at 1/4 tank remaining it would pop up to 3/4.  My Mooney M20F has two transmitters and floats in each tank. Inboard and outboard and they share a ground with the inboard having insulated grommets for the screws, a strap to the outboard and then the outboard has no grommets for insulating as I assume it is grounded that way. Transmitters and gages were sent to Air Parts of Lochhaven for repair. They rebuilt them and replaced the brass floats with a new type of float. When installed they showed empty with 8 gallons and showed 3/4 with a full tank. My tank is 32 gallons. My mechanic tried to adjust the float arm with no improvement and also looked at the gage itself. During the process he saw both individually indicated 0-30 ohms which is correct then the inboard stopped indicating altogether. We are sending it all back to Air Parts. Should this be this hard? Any thoughts? Advice welcome.

[N9660M]

Tony, I've had some similar issues with my M20F.  Was told by the MSC that did my first annual that the floats can be a bear to get adjusted.  As long as they are functioning, they're legal, but I just don't put much faith in them.  The first couple years I had my plane I just calculated fuel remaining based on time of flight and fuel burn rate.

I later installed an EDM-700 with fuel flow, which is great.  Now it's easy to know exactly how much fuel I have remaining.

Take care - Jim

[Lood]

To be honest, I didn't know that accurate analogue fuel gauges actually existed. The gauges on my C172 were similar to its door latches - they were only there because they had to be but it didn't necesarily mean they worked. I can't recall wether the fuel gauges on my Robin worked correctly - I suppose I would've remebered if they did.
So, I just took it for granted when the ones on my Mooney were all over the place from day one. I've actually had the whole cluster serviced and calibrated but the fuel gauges are still indicating whatever they feel like. I just use my self calibrated dipstick together with the JPI EDM700.
I must admit though that it is a source of great and endless frustration and annoyment...

[DonMuncy]

I'm not certain, but I suspect your fuel sensing system works like my K model. On mine, the wire goes from the gauge to the coil in the inboard float, but the gauge there is not grounded. the wire is insulated from the flange with a fiber washer. The wire then continues to and through the outboard float coil and then to ground. The net result of this is that the gauge senses the cumulative resistance of both floats. I couldn't tell from your post if you were aware of this.

[TonyPynes]

Quote: DonMuncy

I'm not certain, but I suspect your fuel sensing system works like my K model. On mine, the wire goes from the gauge to the coil in the inboard float, but the gauge there is not grounded. the wire is insulated from the flange with a fiber washer. The wire then continues to and through the outboard float coil and then to ground. The net result of this is that the gauge senses the cumulative resistance of both floats. I couldn't tell from your post if you were aware of this.

[Mooneymite]

The only airplane I've ever owned with dead-on accurate fuel gauges was an RV-4 with automotive equipment.  It was always "right on".

 

The only fuel indicator I actually trust in my Mooney is the clock, though the recently installed EI fuel flow is proving itself accurate to about .1 gallon/hr. of flight.  The gages are there for legal reasons.  I wouldn't trust them for any serious fuel decisions.

When I first got my Mooney, I futzed with the senders/wiring/gages, etc. endlessly....nothing made them trustworthy.

[TonyPynes]

I would care less but i am about to start IR flight training and really dont want any thing like a gage not working to cause issues.

[M20F-1968]

I would not use the old style fuel senders from the F model, even if they were rebuilt.  I would install the newer style which is in the current production.  The new ones are mostly the same except for the shape of the arm.  There are retrofit numbers for the J (and I believe F) which is the same tank.  I have two extra inboard senders if you would like and 2 outboard senders with straight arms.  You can call me at (617) 877-0025 or e-mail me at johnabreda@yahoo.com  Check with your A&P.  In any case, the newer style senders are much more reliable mechanically.  Design wise, the float arm is shorter and errors are not magnified. 

John Breda

[AmigOne]

For whatever is worth in my 68 Ranger the left fuel gauge works very well and the right one very badly.  Since I have the JPI fuel computer which I know to be very accurate that is what I use.  Also I always fill the tanks after a flight so I know that 2 hrs per tank is safe with at least .45m VFR reserve.  Coming from Oshkosh, 9000 ft, 23/21.5, for test purposes I timed 2.5 hrs on the cruise tank and upon fillup I had 1 gl left in this tank.

[TonyPynes]

I think my longer term plan will be to get a 930 or something for primary but for now I just wanted the appearance that things worked close to as they should. I always use time and power settings to calculate fuel and prob always will as a back up even if I upgrade later. With instrument flying starting soon I want everything as close to good working order as possible. My mechanic just got the senders back after sending them back to Air Parts for issues with the inboard one. Hopefully we will get them set up and working this time. Messing with them has added a month to my annual. I guess that is one way to avoid the heat. Next week I need to be in Savannah to visit Gulfstream...plan on flying myself after some test piloting.

[TonyPynes]

Quote: M20F-1968

I would not use the old style fuel senders from the F model, even if they were rebuilt.  I would install the newer style which is in the current production.  The new ones are mostly the same except for the shape of the arm.  There are retrofit numbers for the J (and I believe F) which is the same tank.  I have two extra inboard senders if you would like and 2 outboard senders with straight arms.  You can call me at (617) 877-0025 or e-mail me at johnabreda@yahoo.com  Check with your A&P.  In any case, the newer style senders are much more reliable mechanically.  Design wise, the float arm is shorter and errors are not magnified. 

John Breda

[TonyPynes]

Quote: AustinPynes

John,

 

You have lots I would love to have. But my budget has me on a one step at a time plan. If I had thought about your senders before paying for rebuilt Iwould have gone that route. If these do not work,might still.

[funvee]

I would not use the old style fuel senders from the F model, even if they were rebuilt. I would install the newer style which is in the current production. The new ones are mostly the same except for the shape of the arm. There are retrofit numbers for the J (and I believe F) which is the same tank. I have two extra inboard senders if you would like and 2 outboard senders with straight arms. You can call me at (617) 877-0025 or e-mail me at johnabreda@yahoo.com Check with your A&P. In any case, the newer style senders are much more reliable mechanically. Design wise, the float arm is shorter and errors are not magnified.

John Breda

Do you have part number for the new ones? Also, does anyone have a drawing of where they are installed and their associated wiring? I have the shop manual but i don't see a detailed drawing.

Thanks

[M20F-1968]

Check with a Mooney service center. I do not have the part numbers just now but the senders are similar but for their shape (straight or bent) and the wire shape. The wiring is the same as the originals. As I recall, the outboard sender is grounded to the airframe. The inboard sender is not,

John Breda

[N201MKTurbo]

Have you checked the gauges themselves? when I had a M20f they were always the problem, they have some cheap little wire wound potentiometers in them that get a bad connection after a few decades.

[captainglen]

N201MKTurbo post mentioned the wire wound potentiometers inside the instrument cluster unit, these are the span adjustments for the  fuel quantity gague and set the full level. The zero fuel quantity is set by bending the float arm. To avoid going back and forth between the two manually bring the floats to the top and adjust the pots to full indication, aduust the bend on the float arms tho jeat touch the bottom of the tank jest as the transmitter reaches the mechanical stop.

[captainglen]

One more thing I should mention is that the gague clusters themselves do not age well. The shafts of the D'Arsonval meters wear allowing radial play. Once the radial play is enough to allow the coil to come in contact with the magnet the meter will stick and tend to move in jumps. I have tried adjusting the shaft end jewels but most of the wear is at the shaft end percision points and the results of adjustment are poor at best. I am considering replacing my entire cluster with MITCHELL GAUGES because my oil temp has already secumbed to this disease.