Moeller Float Gage Accuracy

[DonFromTX]

My newly purchased 12 has the fuselage fuel tank with the Moeller gage. As delivered, it shows about 3/4 full, but it is actually near 1/2 full. I hear that they are so far off as to be useless, but I want to re-label it or something to be more accurate. Has anyone else had this trouble and made a solution?

[tomkk]

I, frankly, pretty much ignore it. Although it goes against every "Thou shalt never rely on your gas gauge" instruction I've ever had, My Skyview (measured) fuel quantity is VERY accurate and I've come to believe. No so with the Moeller.

[Top Cat]

Don
When I first got my SLSA the Moeller gauge was pretty accurate as compared to expected fuel burn and fuel loaded. After three years I've gotten my k-factor down so as the fuel burn I've experienced is reflected on the SkyView EMS and backed up by the Moeller gauge.

That said over this past year my Moeller gauge began to stick or not move. Possibly due to my mechanic removing the tank a couple of times for annual and installing mods.
Lately the Moeller will stick after adding fuel until I repeatedly tap the gauge to make it move to where it should be. In flight the gauge won't move until a full tank has burned down to about 15 gallons then it will move down accurately reflecting tank level.

The RV-12 fuel system has been frustrating in my experience. I'd much prefer to have fixed wings and a fuel tank in each say 12 to 15 gallons with no cabin tank.
Ive managed the fuel with a combination of eyeball, fuel loaded v fuel used , tapping the Moeller, and now fine tuning the k-factor.

[DaleB]

I have three fuel gauges...

1. The float gauge. Displays on the D-180. Very accurate, but only when the fuel level drops down to 14 gallons or less, otherwise it's pegged at full. I use it as my primary indication when I'm flying, after the first hour or two.
2. The D180 fuel totalizer. Fairly accurate, but the more fuel you burn the further off you geet. Fortunately its little white lies tell me I have a little less fuel than I really do. It's close enough that really, if I have to worry about HOW accurate it is I know I'm way too close to empty. And, I don't think it's just the K factor. Sometimes the cruise fuel burn shows what I expect, sometimes it's one or more GPH higher than I know I'm probably burning. I don't know what's up with that.
3. The Moeller gauge. I think it's about right at the bottom end, but all I really use it for is a rough idea of how far I have to go when dumping gas into the tank. It's a nice little double check during pre-flight, but I don't really count on it for any sort of accuracy.

Point is, all three tell me the same thing under all but completely full tank conditions. If I see one out of whack, I know it's time to investigate.

Mine originally had a sight glass too. It's gone. It leaked like a sieve, and was opaque enough to be useless anyway.

[tomkk]

Originally Posted by Top Cat

Don
The RV-12 fuel system has been frustrating in my experience. I'd much prefer to have fixed wings and a fuel tank in each say 12 to 15 gallons with no cabin tank.

I've not had any frustrations with the fuel system - it's worked as advertised without any problems. Having said that, like you, I'd prefer to have the fuel in the wings rather than behind my passenger ...

[Piper J3]

I have four ways to determine fuel quantity before flight: Moeller, sight-gage on side of tank, Dynon D-180, and dip stick.

The only one I completely trust is the dip stick – very accurate / never lies…

[rvbuilder2002]

Originally Posted by Top Cat

In flight the gauge won't move until a full tank has burned down to about 15 gallons then it will move down accurately reflecting tank level.

Originally Posted by DaleB

Point is, all three tell me the same thing under all but completely full tank conditions.

Since the RV-12 fuel tank by design slopes upward as it moves aft, neither the float sensor for the EFIS fuel gauge or the float on the Moeller gauge are at the highest fuel level point when the tank is totally full (the fuel filling the aft portion of the tank is above the highest float levels), so neither will show any change until you have burned off 3-4 gallons of fuel (The Moeller is further aft so it will begin to show a change a little sooner than the EFIS gauge).

[DonFromTX]

Thanks a lot guys, that is very helpful. I have wing tanks in my main RV12 largely for those reasons. The ferry pilot told me the K factor for the red cube is way off, needs a much larger number put in.

[rvbuilder2002]

Originally Posted by DonFromTX

Thanks a lot guys, that is very helpful. I have wing tanks in my main RV12 largely for those reasons.

This is not a problem with the RV-12 (and not exclusive to the RV-12 either... all of the other RV models have gauges that can't read the upper 4 gallons or so because of wing dihedral). When is it that important to have a absolute gauge indication of the first 3 or 4 gallons that get used. The important thing is for accuracy at that last 3 or 4 gallons. The RV-12 tank does well with this.

A long / full span skinny tank in the wing with the dihedral tilt will be effected even worse than any of the other RV's are.

[Pat Stewart]

Just like the wing tanks in most RVs the first 5 gallons or so must be burned before any gauge will be effective. I found the Moeller to be pretty accurate from about ten gallons down. Once you start experimenting with K Factor the fuel burned indication will start to become more accurate but the gauge itself is no different from the Moeller. I always kept track of climb time and cruise time and never took off in the 12 with less than 10 gallons. My 7A with duel Skyviews will only show 15 gallons when full and will not move until it is down to that level but the fuel flow is pretty accurate.