I attached the image of measurements I made with my "G" and its long-range tanks. I'm using the J-Hawk J-Air Fuelhawk 11" Universal AvGas Pre-Flight Fuel Dipstick. Also, I sincerely recommend a Fuel Stop - FuelHawk Saver attached to the fuel dipstick. It would be easy to lose the dipstick in any 337 fuel tank.

This was very time consuming work. Each reading was taken with the dipstick resting in the lateral channel that runs down the length of the wing tank. The lowest reading was made with fuel in that channel, directly below the port.

Use the chart at your own risk. Honestly, I will check the accuracy of my recorded data the next time I have the fuel below the filler ports.

The right gauge has stopped working since I bought the airplane. If the problem is in the indicator, I will install the Aerospace Logic FL212 electronic gauge on my aircraft; it is STC'd for the 337.

I'm glad you mentioned the insight Gem 4 engine monitor. I think I am going to head for that. I like the vibration analysis capability. My fuel gauge gone so I will likely be doing the aerospace logic fuel indicator with CiES probes after the holidays at the same time. (In the meantime, I still need to squeeze ADS-B out in before end of December.)

One thing about the Aerospace logic fuel gauge: per the STC it can be the only fuel gauge installed. So any later upgrade to glass engine management or glass navigation will mean the aerospace logic unit comes out (or you don’t hook up fuel to the fancy glass stuff).

I plan on replacing my capacitance system with CiES probes and then the aerospace logic indicator. The real cost will probably be the probes and wiring. But probes are compatible with a number of systems.

Any recommendations for an electronic fuel gauge?
 

So has anyone pulled the trigger and actually installed the CiES fuel senders yet? I pulled the left tanks at annual to re-cork the tank straps and now the gauges are shot. I am looking at CiES and any other option out there. I still have the Stewart gauges and would prefer something to work with them for now until I am in a position to get an engine monitor. Anybody know of any other fuel sender options?

Yes, I’ve put CiES senders and a JPI960 in my plane. The installation required a little debugging (it turns out that the senders should not be grounded to the airframe - I think that was the problem), but once that was solved they are quite nice. Another Skymaster in the area also upgraded but used three sensors per tank instead of the two per tank that I’ve got and as a result I think they have more accuracy in the middle of the range.