Topic: Condensation in fuel gauges

[andrewjherbert]

Any experts at getting condensation out of fuel gauges?

I've succeeded in getting the circlip out of one gauge but the glass has welded itself to the body of the instrument.  The clip on the other gauge is pretty immoveable and I'm wary of breaking the glass.

We've tried gently warming the gauge with a hair drier: this evaporates the moisture until it gets cold again, the we are back where we started.  It would be much better of we could open up the gauge(s) and dry them.

Andrew

[Nigel Stevens]

Andrew,
I've dismantled six fuel guages to be precise. To get the glass out you have to remove the circlip first. There is a rubber seal underneath the glass and sometimes the  glass sticks to this.
The glass should drop out if the circlip is removed. Paint also infiltrates this area sometimes. I finally freed up a couple of glasses using a fine artists palet knife and a lot of patience, by gently freeing around the edge.
Nigel

[andrewjherbert]

Thanks for the advice. 

I'm doing my repair while the gauge is still in the wing so getting the glass to fall out will require inverted flight   I will try some gentle suction to lift it off the rubber pad.

One circlip comes out easily as it has a 2mm gap so can be levered with a fine screwdriver, the other has essentially no gap in it's circumference so I can see how to get it out   

[Nigel Stevens]

Andrew,
I have not had problems with condensation in the fuel guages, but in my opinion removing the glass will not solve the problem. The glass, dial and pointer mechanism, attached to a magnet, form a capsule held in place by the ring of screws.(inside the ring of bolts) Under this is a large air space with another magnet attached to the rod that comes up from the float system. Two of the guages I dismantled were rusty and corroded in this area showing the presence of water. This dial capsule:bezel unit is attached to the rest of the guage by either a rubber seal, a cork seal or some black gooey substance. (parts vary, yours may differ!!!!)
5 of the six guages I dismantled carried the same part number but differ significantly in the parts some of which are not interchangeable.  If you break a glass you can get new ones made by a glass window and mirror shop.They can cut a circle in a piece of glass of the right thickness and polish the edge to avoid you cutting yourself on installation. I've have had glasses made in this way for two of the instruments in the instrument panel. One of the fuel guages I had contained a perspex "glass" I think this was someone's local bodge since the perspex is in contact with gasoline and some of the hydrocarbons in gasoline are not "perspex friendly".
I have not found any documentation on the guages so was 'flying blind" when I dismantled them. Two of the dials I have are marked "Smiths" the others are blank. I thought that an AHO part number indicated a Dunlop origin (as per the brake system) but I don't see any Dunlop involvement in the guages. can anyone put me straight on this point?
Nigel

[Bob]

John Henderson and I dismantled a couple of gauges recently,I replaced the glass with one from a 70's Smiths Instruments car gauge ( ammeter from a Jag I think) most 60's and 70's instrument glass seems to fit! 

[andrewjherbert]

I managed to get both glasses out in the end.  Using a thin palette knife to lever out the clip woked well.  One came out easily the other took a lot of gentle wriggling.  Once the clips were out I lifted the glasses out using strong sticky tape.  I wiped the glasses dry and the instrument itself, left for a while and then re-assembled.  Seems to have done the job ok.

Thanks for all the advice.

Andrew

[Dick Gower]

These originally used a square sectioned rubber seal with a step in it to seal the glass but these are not very effective.  The trouble is that water sits in a natural well above teh glass and slowly makes its way inside with temperture changes.

The best answer is to dry them out and assemble with a flexible adhesive.

I used Selleys "All Clear" which is flexible and bonds to glass very well.  I will try to find out the details so that you can find an equivalent.