Need Help - Fuel Gauges only go to 17

Any DA42 related topics.

Moderators: Rick, Lance Murray

Post Reply
NatWolfe
1 Diamond Member
1 Diamond Member
FIRST NAME: Nathan
Aircraft: DA42MPP
Registration: NotPrvd
Airport: KLVK

Posts: 1
Joined: Tue Mar 30, 2021 9:45 pm

Need Help - Fuel Gauges only go to 17

Post by NatWolfe »

I have a 2015 DA42 NG. On a recent cross country over the Rockies I encountered a bit of turbulence (Light but steady chop - and I'm not certain this fact is relevant at all to the problem) I was cruising at FL180 and a bit over an hour in I looked at the fuel gauges (Which were always SPOT on) and they read 17 both L&R. Mental calculation calculated that as smelling correct and it aligned with with fuel computer so I continued flying and about 30 mins later I checked again.... Both Fuel Gauges read 17 Gal remaining.

This was obviously incorrect so a quick calc told me I should be burning a gallon a side every 8 mins (ish). So I kept an eye on it. The gauges persisted at 17gal / side.

The fuel gauges continued to read 17 Gal remaining for the next 30 mins. I am equipped with aux tanks so I started moving fuel from my full aux tanks into the mains. (This happens at 1gph / side and I calculated the number of minutes until the tanks should read 18-19 gal remaining and exactly on schedule the fuel levels began to rise in the mains. I've performed this test multiple times with the same result.

I took the plane to the Diamond premier shop and told them both gauges started acting up at the same time on the same flight and the problem has persisted since it started. They drained the tanks and refilled them while checking the senders and they've indicated to me that the senders are working correctly and to talk to Garmin (Avionics shop) about it. (Sigh)

1) Any idea what might have caused the problem? It's not like that was the first time I'd been in turbulence?
2) Anyone else have this problem in that past and have any idea what fixed it?
3) It seems at least somewhat plausible that this could be a Garmin / software issue, but I'm hesitant to plop the aircraft into the avionics shop with instructions to "go find the problem."
4) It seems like If I'm going to go that route I should have them just reload the software for the G1000 in full (Which I've heard is a custom load from Diamond? Anyone know that for sure?)

Anyone Have Thoughts / Experience with this sort of issue?


Thanks,

Nat
User avatar
CFIDave
5 Diamonds Member
5 Diamonds Member
FIRST NAME: Dave
Aircraft: DA62
Registration: N62DV
Airport: KJYO

Posts: 2179
Joined: Wed Nov 07, 2012 3:40 pm
Has thanked: 144 times
Been thanked: 954 times

Re: Need Help - Fuel Gauges only go to 17

Post by CFIDave »

There's probably nothing wrong with your fuel gauges. There's a "dead spot" that normally causes the gauges to read 17 gallons for a long time as you continue to fly and consume fuel. I'm really surprised that Garmin and Premier couldn't have told you this.

Each 25 gallon aluminum fuel tank in the wings is actually 3 chambers interconnected via short hoses. The inboard chamber has a fuel level sensor (capacitive rod) that will read up to 17 gallons total. But there's a totally separate fuel level sensor rod for the 5 gallon outboard chamber (on a Lycoming DA40 that would be the "extended range" tank, but the DA42 has the same configuration).

As you consume fuel and empty the outboard and middle chambers, the G1000 MFD fuel gauge will show 17 gallons for a long time because the capacitive rod installed in the inboard chamber hasn't yet sensed fuel being consumed. The G1000 software attempts to hide that there are actually 2 fuel level sensors in each wing, but can't overcome the "dead spot" in the middle chamber between approximately 17 and 20 gallons (where there's no sensor) where it's not possible to provide an accurate reading.
Attachments
Screen Shot 2021-04-09 at 10.30.57 AM.png
Last edited by CFIDave on Fri Apr 09, 2021 2:40 pm, edited 1 time in total.
N62DV DA62 62.056
N42DA DA42-VI 42.N117 (sold)
N811ET DA40 XLS 40.874 (sold)
KJYO Leesburg, Virginia
User avatar
Chris
5 Diamonds Member
5 Diamonds Member
FIRST NAME: Chris
Aircraft: DA42NG
Registration: N449TS
Airport: KHIO

Posts: 648
Joined: Sat Jun 19, 2010 3:34 am
Has thanked: 426 times
Been thanked: 206 times

Re: Need Help - Fuel Gauges only go to 17

Post by Chris »

I have less than 30 hours in my NG, so I'm by no means an expert, but I've noticed this exact same behavior at least a couple of times. The fuel gauges "stick" at 17 gals per side for a while and then start to catch up with reality a bit later. I've attributed this to the fact that only the inner and outer chambers of the fuel tanks have level sensors, so there's some imprecision when the outer one empties.

Ah, I see that Dave just posted a full explanation.
Chris
N449TS / DA42-NG / 42.AC049
KHIO
User avatar
ememic99
5 Diamonds Member
5 Diamonds Member
FIRST NAME: Emir
Aircraft: DA42
Registration: SEMAD
Airport: LDZA LDVA

Posts: 691
Joined: Wed Apr 09, 2014 10:31 am
Has thanked: 154 times
Been thanked: 229 times

Re: Need Help - Fuel Gauges only go to 17

Post by ememic99 »

That's normal behaviour as CFIDave explained. Fuel gauges are kind of accurate between 25 and 19 gallons and then when they start to show below 17 gallons per side but for both these ranges the accuracy has to be taken with grain of salt. You can rely on fuel totalizer - check it when refueling to confirm correct consumption.

Regarding your transferring fuel from aux tanks to wings, you should start this earlier in the flight to confirm availability of this fuel and proper pump functioning - you don't want to learn too late that the pump doesn't work properly and that aux fuel is not available. Moreover, when flying high, aux fuel will be much colder and you want to have decent quantity of warm fuel in the wings to mix with in order to avoid low fuel temperature.

I turn it on once fuel reaches 18 gallons per side and usually both pumps turn off automatically when the level reaches 22 gallons. Right hand side pump in my case is a bit slower, lagging behind left one for a minute or so. On few occasions I noticed one pump didn't turn off automatically when same level was reached (overfilling one wing) and I had to turn it off. Of course, usually pump switches have to be turned on and off simultaneously.
User avatar
photoSteveZ
3 Diamonds Member
3 Diamonds Member
FIRST NAME: Steve
Aircraft: DA62
Registration: N691DA
Airport: KEIK

Posts: 66
Joined: Wed Dec 23, 2020 4:10 pm
Has thanked: 86 times
Been thanked: 48 times

Re: Need Help - Fuel Gauges only go to 17

Post by photoSteveZ »

I'm glad to see this thread, because in the three months I've been flying a DA62 I have noticed the hitch in the fuel gauges' gitalong around 17 gallons, but didn't think it through. After reading these posts I went out to the airplane, hooked up ground power, read the fuel gauges (17 gal each main, 18 gal each aux) and transferred enough fuel from the Aux tanks to bring the Main gauges up to 19 gallons. Turns out I had about four gallons less fuel in the mains (two gal. less, each) than I thought...if I am to believe the gauges. ;)
User avatar
CFIDave
5 Diamonds Member
5 Diamonds Member
FIRST NAME: Dave
Aircraft: DA62
Registration: N62DV
Airport: KJYO

Posts: 2179
Joined: Wed Nov 07, 2012 3:40 pm
Has thanked: 144 times
Been thanked: 954 times

Re: Need Help - Fuel Gauges only go to 17

Post by CFIDave »

photoSteveZ wrote:
Mon Apr 12, 2021 11:00 pm
I'm glad to see this thread, because in the three months I've been flying a DA62 I have noticed the hitch in the fuel gauges' gitalong around 17 gallons
Yes, the DA62 main fuel tanks and gauges work exactly the same as for the DA42, with the same unusual behavior around 17 gallons. The only difference is that DA62s with NXi also have AUX fuel tank gauges (that are lacking on all DA42s and Legacy G1000 DA62s).

But the totalizer amount tends to be spot-on.
N62DV DA62 62.056
N42DA DA42-VI 42.N117 (sold)
N811ET DA40 XLS 40.874 (sold)
KJYO Leesburg, Virginia
Post Reply