Remove tank screw cap. Any suggestions welcomed

[idomeneus5]

Hi all, this could go in almost any of the forums, but as the "tank" is in a 26ft sunbridge cruiser I'll start here. The tank in question is a 136Litre fresh water tank. I wish to add an electronic water level gauge, as I'm sick of running out and the associated air locks. System is a kit (Jaycar, similar to Maplins I guess) and requires installation of a substantial vertical sender. Here lies the problem. The aluminium tank has a screw in cap which I am unable to remove and this would be the best place to install the sender, thus not requiring the drilling of a hole or the cutting of a panel with the resultant filings dropping into the tank. I cant remove the tank as its inside the forward v berth bunk base. Original access to the cap was via an inspection port in the bunk top. I have since cut a 3ft x 2ft panel out of the top of the v berth to allow better access, I'll turn it into a shallow storage area. [img]/forums/images/graemlins/confused.gif[/img] Its not a left hand thread, Stilsons/footprint wrenches wont budge it, even with liberal doses of WD40 etc. Dont want to apply too much force as aluminium walls are fairly thin, female thread assembly has been welded into the tank. Any suggestions gratefully accepted, Peter.

[Moonshiners]

gentle heat followed by reasonable force with wrench (not enough to cause damage, if that doesn't work, gentle heat followed by a bag of ice a good few taps of a hammer and reasonable force with wrench.

But the hot or hot and then quickly cold, will budge most threads. But its' only general advise for shifting stuck threads.

EDIT - Don't forget to let the tank vent as much as possible - filler cap off etc...

[coliholic]

Build a little wall around the cap using blue tack or putty or something. Then fill the resultant well with either Coca Cola or alloy wheel cleaner. Leave overnight and I betcha it comes undone.

[DavidJ]

Heat up with something like a paint stripper electric gun. It will be 'softer' than a gas blow torch. After heating and cooling a few times it will spin undone. Aluminium has huge expansion qualities. Can you heat the outside area and keep the cap cool in some way?

[Roj1]

Vinegar is very good at releasing ally fastenings. Also try heat - apply stilsons and as you apply pressure get someone to gently tap all around cap.