Fuel gauge magnets

[airlaw]

Aloha: I have one fuel gauge that apparently has a weak magnet. I haven't drained the tank to inspect, but we had this problem before.
Can you get these parts; the article in 2d quarter 2012 news did not cover this as he found a working replacement.
Any ideas would be appreciated. Mahalo and Aloha. David Bettencourt

[airlaw]

I have two 1952 170B models. I haven't had the gauge out in a while, but I'm sure it was a magnetic connection. David

[3958v]

The magnet may just be loose on the shaft. If that is the case a dab of proseal used to seal fuel tanks fixed mine years ago and it still works fine over 10 years
later. Bill K

[blueldr]

Aryana,
The float arm on the inside of the wing root mounted fuel gage is geared to a rotating magnet that transfers the flux through the aluminum housing to a following ferrous needle piece on the inside of the cabin so there is no requirement for a sealed rotating shaft into the fuel compartment.

[Bruce Fenstermacher]

Here is the back side of the fuel gauge that is inside the tank. What is not seen is the end of the arm with a cork or float that is attached to the rack. The rack turns the pinion which turns the shaft with the U shaped magnet. As already stated the needle on the other side is turned as the flux from the magnet moves.
Note: This is a genuine sold to Cessna, Rochester "Scott" type. Rochester gauges available today have a different arrangement to turn the magnet and needle.

Wondering why this magnet would loose magnetism to the point it wouldn't work when many many others have not. Wondering if something has not just stuck the needle. Wondering if the magnet is just not turning as John stated happened to his. So many things to ponder.

I'd get a magnet and see if the needle can be moved. Then I'd insure the magnet is attached to the shaft. After that I'd look for a way to restore magnetism to the magnet. Seems I did that a time or two with coils of fine wire energized with DC current while coiled around a piece of ferrous metal (screw driver) when playing with my Lionel trains and learning a lot about electricity. You could experiment or maybe find an instrument shop that also repairs speedometers/tachometers and see if they can help. You see speedometers/tachometers work the same way with the needle being spring loaded and turned against the spring by the flux of a turning magnet. Keystone Instruments in Lock Haven, PA has a WWII era device for magnetizing such instruments.

[Bruce Fenstermacher]

One of my fuel tank needles is rock solid and stable, but the other bounces around a lot more. Is that the symptom of a bad magnet?

The age old question. How can we make these gauges work better.

I suspect that your gauge that doesn't bounce is not as loose (worn) as the other. The resulting drag on the mechanism in effect acting like a damper so the float does not freely bob on top of the fuel as it sloshes about. But instead takes a steady level consistent with the quantity of fuel at rest.

With the gauge I have in hand I can rapidly move the float up and down and I can see when done to the extreme that the needle leaves the field of flux and is not aligned with the magnet but it quickly returns. In other words it bounces but the needle movement is so quick that you can hardly see the needle. But if I move the float up and down at a slower rate, one that I imagine the fuel level really takes, the needle moves in a fashion I'm more accustomed to seeing. That being the needle bouncing about a 1/4 to 3/8 its travel in one direction then back. I suppose a weak magnet could cause excessive needle movement but you'd have to prove it to me.

I normally swag the fuel level at about half this moving travel on the gauge. Then compare it to time flown with a known fuel burn and known quantity of fuel at start. Relying on the time fuel burn to be more accurate and ruling. I would land before I think I'm out of fuel by time/fuel burn or the needles say I am which ever indication happened first.

[daedaluscan]

I am a new pilot and scared to death of it all going quiet because I didnt put gas in.

I have not really stretched range anywhere yet and I am consistent about dipping the tanks anytime I stop. The gauges really seem vague at best, they jump around so much that I really am checking to see that they are still jumping around rather than to get an accurate measure of fuel in the tanks. I actually write down fuel quantity at takeoff on my kneeboard but I would sure like one of these:

http://buy-ei.com/portfolio/cgr-30p-overview/

However at $4000+ my feeling is I am better off spending that kind of $$ on gas and actually flying. I went for a checkride with my tailwheel instructor the other day as I had done 100+ hours on my own and he had me doing circuits in 20G30 at 60 degrees to the runway which made me realise that I am still learning at a fast rate.

Does anyone have any other suggestions for a fuel totalizer?

Charlie

[lowNslow]

I'd save my money and skip the fuel flow meter. You'll find that the fuel flow is very consistent with the tach hours. On my airplane I run very close to 7.5 gal/tach hour which with full tanks gives me 4 hours of flight with a comfortable 45+ minutes reserve. If record your tach time every time you refuel you will get good fuel flow for you aircraft. You may burn a little more fuel if you are just doing touch and goes and lots of short hops but I find there is very little difference.

[hilltop170]

I am a new pilot and scared to death of it all going quiet because I didnt put gas in.............Does anyone have any other suggestions for a fuel totalizer?

Charlie

The two things that reduced my inflight anxiety more than anything else was the GPS so I know exactly where I am at all times and the fuel flow computer so I know my fuel status at all times to within a gallon. Sure, I know the different ways to calculate position and fuel state, I did it for around 30 years without help and never had any serious problems with any of it. That doesn't mean I never had any anxiety though.

Now that I know where I am and my fuel status, I can worry about other things like where is the cheapest gas and best lunch stop.

For a few hundred dollars, EI sells the 2-1/4" dia FP-5L-60 fuel computer. It is worth the money.

[170C]

This post brings up a question. What does the magnet look like? Years ago one of my gauges ceased working so I removed it per Steve Grimsley's procedure. I did not bend the arm, rather removed the old cork/float by modifying the end of the rod. Bought a couple of corks from Michaels, glued them together, sanded them to fit the profile of the old one and coated it with several coats of varnish or something similar. I did note that there were two metal items (sort of like tacks without the heads) imbedded in the cork. I removed them and put them in the new cork/float. Are these the magnets? I put the cork/float back on the rod followed by the small washer and flattened the end of the rod to retain the washer and cork/float. My gauge had worked just fine since I did this approximately 15 years ago.

[Bruce Fenstermacher]

Frank,

Looking at the picture I posted, on the shaft at the end near my hand you will see something that looks like a wing nut. That is the magnet.

[170C]

Thanks Bruce. That is something I missed. I guess mine must be working OK.

Frank

[GAHorn]

... I did note that there were two metal items (sort of like tacks without the heads) imbedded in the cork. I removed them and put them in the new cork/float. Are these the magnets? I put the cork/float back on the rod followed by the small washer and flattened the end of the rod to retain the washer and cork/float. My gauge had worked just fine since I did this approximately 15 years ago.

They are not the magnets being discussed. They are bob-weights designed to dampen the movement of the corks.
The best solution for cork floats is to order the new nitrile (plastic) floats for these gauges from Spruce.

The best solution for complete replacement is to order entire mechanical gauges from Spruce and modify them. IMO

[n2582d]

Revisiting an old thread here. My gauge looks a bit different than the one Bruce pictures on the first page of this thread.

The common understanding has been that the “U” shaped metal on the shaft is magnetized. Mine was not. Probably why the needle doesn’t swing as the float moves up and down. Any suggestions for magnetize it? With my luck I’ll get the polarity wrong. I had thought that the U-shaped part acted on a steel needle. What I found though was that the needle is brass and therefore non-magnetic. Turns out there is a small disc attached to the brass needle that is a magnet.

There was discussion about the “bob-weights” in the float. Both 7/8” nails — looks like concrete nails— weighed 0.1 ounce together. Wondering if I should add them to the new floats I bought from Aircraft Spruce.