Right fuel gauge needle swinging wildly

[joegoersch]

I have an 1989 J.  While in level flight with about 10 gallons in the right tank, I noticed the Right fuel gauge needle indicating 10 gallons, but then it would swing rapidly to beyond "full".  The needle would then rapidly return to 10 and then a few minutes later swing wildly back to above full.

This would happen even when level and not in turbulence, so I don't think the fuel was sloshing around.

Any thoughts ?

[ArtVandelay]

This can be sign your inboard fuel sender needs an overhaul. Because they are always submerged in avgas as opposed to outboard senders, the inboard senders overhauling more often.


Tom

[Duane Baker]

Both of my electric gauges do that, I thought it was normal for a Mooney. The mechanical gauges on the wing work well. seeya Daune

[joegoersch]

1 hour ago, ArtVandelay said:

This can be sign your inboard fuel sender needs an overhaul. Because they are always submerged in avgas as opposed to outboard senders, the inboard senders overhauling more often.


Tom

Is this a big deal (i.e. expensive) ?  I have wing fuel gauges which work fine and a fuel JPM that very accurately tells me my total fuel...so I don't know if it's worth it.  It's really more of an annoyance than anything else...

 

Thanks

[ArtVandelay]

Is this a big deal (i.e. expensive) ?  I have wing fuel gauges which work fine and a fuel JPM that very accurately tells me my total fuel...so I don't know if it's worth it.  It's really more of an annoyance than anything else...
 
Thanks

It’s been a couple of years, but it was $165, took about a week or so. Place in Pennsylvania, don’t know the name offhand. Probably during an annual is a good time to do it.


Tom

[Andy95W]

http://www.airpartsoflockhaven.com/fuel-components

[steingar]

Years ago I asked Don Maxwell himself what I had to do to the Mooney to get the gauges to indicate whether there was fuel on board.  Haven't actually done what he said to do, though it is on the list.  I have a fuel stick and a watch.  I'm content.

[carusoam]

Having working fuel gauges is critical for not joining the special club... 

On the low cost side of things...

The airparts of lockhaven OH has been a great route.

If you are into electronic upgrades... and considering an engine monitor like a JPI 900... consider adding the Cies float/sensor option...

For second opinions...  a FF/totalizer is a great way to know how much fuel you are burning...

All in...  you can have two systems to know your fuel level... and a third system that can tell you how much fuel has been burned...

The Cies system is accurate to one gallon, Same with a well calibrated FF gauge...

 

Before spending money... and dreaming big...  consider pulling and cleaning the sensor that is giving you the problem... it might be getting dirty and flopping to infinite resistance in some locations...

PP thoughts only, not a mechanic...

Best regards,

-a-

[anthonydesmet]

As Carusaom stated, check your connections inside the cockpit along the passenger side lower bulkhead.  I had the same issue with my left wing.  I pulled the connector and ground, cleaned with electrical cleaner and small wire brush and that fixed the issue.  

The JPI is great but remember the “total” isn’t the actual measured total in the wing rather the measured total based off your fuel burn and initial pilot totalizer setting.  

Plus your connection may result in the fuel total gauge swinging from full to empty and setting off your fuel low red light.  Annoying and disturbing in flight and one should never get in a habit of flying with a red caution light as a normal practice .......just my two cents.....

[ArtVandelay]

The JPI 900 does both: senders and fuel flow totaling.

 

If its a bad ground connection, which is common to all 6 gauges, I would expect more than just 1 gauge to show symptoms. If it’s a bad connection to sender, I would expect to see problems always, not just when fuel is low.

 

Cies are close to 500/each, in the J that’s $2000 plus labor, the OP clearly indicated he didn’t want to spend a lot of money, Cies plus JPI 900 would run around $12,000...pretty sure that qualifies as “a lot of money”.

Tom

 

[joegoersch]

5 hours ago, anthonydesmet said:

As Carusaom stated, check your connections inside the cockpit along the passenger side lower bulkhead.  I had the same issue with my left wing.  I pulled the connector and ground, cleaned with electrical cleaner and small wire brush and that fixed the issue.  

The JPI is great but remember the “total” isn’t the actual measured total in the wing rather the measured total based off your fuel burn and initial pilot totalizer setting.  

Plus your connection may result in the fuel total gauge swinging from full to empty and setting off your fuel low red light.  Annoying and disturbing in flight and one should never get in a habit of flying with a red caution light as a normal practice .......just my two cents.....

I have a JPI, but it just measures FF and keeps track of total (yes-based on fuel burn).  Plus the wing fuel gauges.  So four total fuel gauges (2 cockpit, 2 wing and JPI giving total). This is a lot more than most planes...

Great idea to clean connections.  Will try.

[skydvrboy]

Having just worked on my fuel gauge system, I can tell you they are really simple.  There are two fuel senders that each measure 0-30 ohms placed in series.   The gauge is just an ohm meter that reads 0-60 ohms (0 being empty - 60 being full).  If your gauge is jumping and pegging past full, it is because you are intermittently getting too much resistance (likely infinite).

As previously mentioned, pull the side panel and check for a loose wire or poorly crimped eyelet.  If you don't find anything there, pull it and clean it.  If you still have issues, repeat with the outboard sending unit, but it's most likely the inboard.

[anthonydesmet]

Since we are having a fuel discussion I thought I’d also throw this out to the group as a fun flight activity next time your out.....most of you might already do this especially if you learned to fly back in the day before JPI’s and when fuel totalizers were sh*te.....I.e. the Tomcat....

i still push my wrist stop watch and cockpit timer before engine turn over....I know what start, taxi, takeoff and climb fuel should be to the mid-teens based off pre-flight calculations and just knowing my airplane.  I also know what my fuel flow usually is based on MAP, RPM, TIT and CHT’s.  So every half hour through a 4 to 5 hour flight when I switch tanks I do a mental calculation and add up where I think I should be for total fuel burn based on time of flight and subtract it from my 75gal useable.  Then I take a look at the JPI and see how far off my mental calculation is from the JPI......just makes me feel better knowing if my gauges froze (or started swinging and were unreliable) and my JPI started acting up I still would have a pretty solid assumption of what my fuel state is.  Plus the more you practice the more confident you’ll be if the situation ever occurred. Also makes me feel better not being dependent on technology.....kind of back to the days of clock to chart to ground/VOR.  Maybe having experienced a total electrical failure in the middle of the Pacific has something to do with it also....

The last exercise is to also mentally calculate your total flight fuel burn (I usually do this during my turbo cool down) and see how it compares to the total fuel at the fuel pump when you top off......

[tmo]

11 hours ago, anthonydesmet said:

I usually do this during my turbo cool down

I see what you did there with that thread drift attempt ;-)

[anthonydesmet]

I see what you did there with that thread drift attempt ;-)

Hah! I guess I did. It was late last night. Apologies to the group


Sent from my iPhone using Tapatalk

[cliffy]

One of the first things I did when I got my Mooney was to time my fuel burns by the hour. Since my flight profile 95% of the time is the same I'm confident in the accuracy. I'd T/O, climb to @ 10,000'  and fly for 1 hr total then switch tanks and land before another hour passed. Fill the T/O tank and record the burn in that tank and estimate what the burn was per hour in the other tank by the flight time. Next flight I;d do the same and fly the second tank (in cruise) for 1 hour  and switch back to the T/O tank.  Land a refill the 2nd hour cruise tank and check fuel burn. I did this all the way to 4 full hrs of flight time (and repeated the scenario a couple of times for a better baseline). 

I know for a fact that my airplane (the way I fly it ) burns 10 gallons the first hour, 9 gallons the second hour and 8 gallons for hours 3 through 5. 

My fuel gauges are "old school" but have been repaired by Lockhaven and I know they work well enough for me to keep track of any leaks above the fuel burn. "Old school" gauges can be checked for accuracy at annual if needed or wanted. 

I also have an EI FP5 that comes out within .1 or .2 gallons of the actual fuel burn.  I also WATCH my "old school" gauges as at the very least they will show the gross quantity in the tank (if not down to a tenth of a gallon). Unlike someone mentioned here that filled their airplane at night and didn't even take the time to look at the gauges before flight the next day.  A habit developed a long time ago during runup at the end of the runway to call out the fuel selector position by touching it and then pointing to the selected tank and calling out the amount of fuel in that tank. "Right tank selected. right tank 3/4s full"  No different than in the airline business of pointing to the altitude selector on the autopilot after resetting to verify that it was set correctly. 

Now if someone wants to fly right down to the legal 30 min min for day VFR  then the digital senders make a lot of sense. Can't knock them even if one just wants them. 

[Guest]

On 1/27/2020 at 12:11 PM, joegoersch said:

I have an 1989 J.  While in level flight with about 10 gallons in the right tank, I noticed the Right fuel gauge needle indicating 10 gallons, but then it would swing rapidly to beyond "full".  The needle would then rapidly return to 10 and then a few minutes later swing wildly back to above full.

This would happen even when level and not in turbulence, so I don't think the fuel was sloshing around.

Any thoughts ?

The inboard transmitter is electrically insulated from the wing with small nylon bushings, a ground wire runs to the outer transmitter, then ultimately to ground.

Start with cleaning all of the ring terminals and see if this cures the issue.  If not, gain access to the back of the instruments and switch the wires on them to verify the gauge or system.

Clarence

[jkarch]

The one big pain here is you have to remove the interior to mess with the gauges. I’d assume removing the inboard sender also requires a reseal in that location and you probably want to do this with an empty tank too!

-J

[cliffy]

Yes but the reseal is treating the gasket with Titeseal and screwing it back in.