One of Mooney’s best kept secrets is their fuel gauge is their retrofit kits.  Pre “J” models are notorious for troublesome fuel gauges that can be unreliable and unserviceable.  Money has an upgrade kit that allows the installation of wing mounted gauges as used in the new models.  These gauges are very accurate and viewable from inside the cockpit as well as during preflight.

Kit Number 940037-501

Kit #940037-501 is for “C”, “D”, “E” and “G” models. The kit is complete with two wing mounted gauge assemblies with dial faces, two gaskets and necessary hardware.  See Fig. 1  On these models the fuel tank filler opening is located in one of the wing fuel tank access panels.  See Fig. 2 The gauge assembly can be installed through this opening without removing the panel and disturbing the sealant on the access panel.  Unfortunately, this retrofit kit can not be installed in aircraft fitted with bladders.

Cost of this kit is $267.84.  Estimated time to install is 1½ to 3 hours each side.

Kit Number 640043-501

Kit #940043-501 is for “F” and “J” models.  This kit contains the same gauges, gaskets and hardware as the previous kit and PRC, fuel tank sealant.  The fuel tank filler on the “F” and “J” is located ion an outer bay of the fuel tank and is not located in an access panel.  On these models the gauge will be located in a panel, but the panel must be removed for installation.  These installations require the gauge and access panel to be sealed with the supplied PRC sealant. See Fig. 3

Cost of this kit is $280.07.  Installation time is estimated from 2½ to 4 hours each side.

Kit Number 940043-503

Kit # 640043-503 is for the “K” models, S/N 25-0001 through 25-0446.  Installation for the “K” model is the same as the “F” and “J”.  The difference in the kits is that the “K” kit uses a different gauge.  Cost for this kit is $287.37.  Installation time is estimated at 2½  to 4 hours.

My estimated time to install these kits is based on how much time it has actually taken us to install the kits.  Times vary due to the condition of the fuel tank, drilling access panel screws and replacing damaged sealed nut plates.

How do they work?

The fuel sending unit is a conventional flat type.  The unit is mechanical and requires no electrical power.  The float is connected to a disc that rotates with float movement.  The disc contains a small magnet.  The fuel quantity indicator located at the top of the sending unit has a metal needle.  As the float moves in the tank, the disc with the magnet rotates and the indicator needle follows the magnet.  There is no mechanical connection between the indicator and the tank-sending unit.  If the indicator is damages or fades, it can be changed by popping the indicator out of its socket with an awl or ice pick.  The replacement indicator (Fig. 4) is installed using a small amount of RTV sealant and popping it back in the socket.  Cost of a replacement indicator is approximately $30.00 each.

Compared to the price of other aircraft parts, these fuel gauge retrofit kits are an economical and reliable alternative to faulty fuel gauges.

SPECIAL NOTE:  This article was written in March 2003.  Price references are strictly for that time period only.