LH Fuel gauge shows only 18gal when filled 25

[NicoN]

We have a 1980 M20K with 72gal tank capacity.

One or 2 years ago the tanks were re-sealed due to fuel leak.

The other co-owners tell me that since then the left tank is showing 18gal max., even when filled with more.

my own experience is similar. We always fill both tanks with 25gal.

The RH fuel gauge is showing 25gal as expected, while the left is showing - surprise -  18 gals, which is simply half of the complete capcity.

In flight, I think the indication for LH is quite fast moving  to lower numbers, but I did not take the time to Monitor thsi in accordance with fuel flow. I also did not try what happens when the fuel gauge says "0". Still Fuel for about 45min in that tank?

As I have a maintenance Manual for the m20K, I know that there are 2 fuel senders on each side and that they are wired in series.

But the Manual does not give substantial Information on typical failure situations.

Can the above described symptoms be tracked down to a specific fuel Sender and what Kind of Problem can be the reason? Is it the iB or OB fuel Sender?

broken wire? Or simply a fuel arm which stucks to the bottom of the tank?

[steingar]

One year at Oshkosh I asked Don Maxwell what to do to make the fuel gauges show that there was actually fuel aboard the aircraft.  Judging from the reaction from the audience I surmised that I wasn't the only one with that particular problem.

[N201MKTurbo]

They didn’t install the inboard fuel sender correctly. It needs insulators to isolate it from ground. If they ground the sender it will do what you describe.

[NicoN]

You have a distinct opinion whta causes the Problem.

Please excuse my stupid question; I am not english native speaking.

I think, "insulator" is meant electrically while "gasket" means something different.

Is there a drawing available where I can see what is needed ? I guess this means one wire goes to the fuel Sender while the Body should be isolated from the aircraft Body?

is there a part I have to order?

[DualRatedFlyer]

20 minutes ago, N201MKTurbo said:

They didn’t install the inboard fuel sender correctly. It needs insulators to isolate it from ground. If they ground the sender it will do what you describe.

Is this true only for the inboard, our could the inverse situation apply -- i.e. outboard is grounded and inboard is not.  Just curious as to why you think its the inboard - i have a similar issue.

[N201MKTurbo]

You should search for previous posts. It has been discussed quite a bit.

The fuel senders are wired in series. The outboard sensor is grounded. Its wire is connected to the inboard sender's mounting flange. the inboard sender is insulated from ground with the gasket and insulating washers on the mounting screws. If they neglect to install the insulating washers, it grounds the inboard sender and shorts out the outboard sender. This will show that the outboard sender is empty.

[NicoN]

This sounds doable.

I do not have a Manual at the Moment.

What size of screws are used? I think, what I Need are "shoulder washers", right ? Size ?

Another question: Is it possible to do the work without emptying the fuel tank? I mean, put the insulating washer in screw after screw without removing the fuel Sender and gasket.

[N201MKTurbo]

https://www.alliedelec.com/abbatron-hh-smith-2535/70210044/

http://www.abbatron.com/products/54-insulated-washers/305-insulated-washer

These are the insulators specified in the parts manual.

 

Edited June 29, 2018 by N201MKTurbo

[mooney2201]

want to end this problem....install CEIS FUEL SENDERS......DIGITAL SENDERS

[ArtVandelay]

These are the insulators specified in the parts manual.
 

I had a problem when tightened down, the insulators pushing through allowing contact, I had to add an additional plastic washer.

[N201MKTurbo]

3 hours ago, teejayevans said:

I had a problem when tightened down, the insulators pushing through allowing contact, I had to add an additional plastic washer.

It has been a while sense I installed some new ones, but I think they are a bit long and I had to trim the ends a bit.

[1964-M20E]

go look at this topic and look at the schematic I attached.   I just solved a similar issue.  Your outboard sending unit wire connected to the inboard sending unit is grounded somewhere. 

Something on the inboard sending unit housing is grounded.

Has the inboard sending unit been removed recently?

Has the wire from the outboard sending unit been disconnected and reconnected recently?

C

 

[1964-M20E]

23 hours ago, N201MKTurbo said:

https://www.alliedelec.com/abbatron-hh-smith-2535/70210044/

http://www.abbatron.com/products/54-insulated-washers/305-insulated-washer

These are the insulators specified in the parts manual.

 

great link

Just checking though don't we need the ones that fit #10 screws?

https://www.alliedelec.com/abbatron-hh-smith-2537/70927493/

[N201MKTurbo]

4 hours ago, 1964-M20E said:

great link

Just checking though don't we need the ones that fit #10 screws?

https://www.alliedelec.com/abbatron-hh-smith-2537/70927493/

This is from the parts catalog.

MS35206-327 - Non-Structural Pan Head Screw 6-32 X 9/16 - Cadmium II Plated (alt part # AN515-632R17)

MS35206-231 is 5/8 long

[NicoN]

To bring this Topic to a positive end, I can Report "Mission completed"

I had to remove the whole lower interior side Panel including the air vent in the foot room (correct?) to get Access to the fuel Sender.

And indeed: All but one screws had the insulating washer installed. The last had not!.

After isolating the screw my simple "continuity tester" still showed me a Connection between the housing and my screws.

But that effect came from the nearly empty tank. Using an Ohmmeter gave me about 9 Ohms.

Now the fuel gauge Shows the full range!

I am happy!

Thank you for all your help!

[Raptor05121]

Excellent job, MS!