Stainless fill cap for water tanks

[3rdCoastBorn]

Hi all,

I'm having issues removing the stainless fill cap on the starboard side. Its completely stuck. Any recommendations on removing? The port side and mid tanks have plastic fill caps that remove easily. Trying to get it out without having to remove the hose and female fitting. Even if its removed it will be hell to get out. Might have to replace the whole fitting. Any help is appreciated.

[S/V AMITY]

  Try knocking the cap with a hammer and a brass or other soft metal drift.  That should break it free.  Plan B: try a bit of PB Blaster and gentle heat around the perimeter of the deck fitting (not the cap).  Knock the cap again with the hammer & drift.  Keep at it and you should be successful.  Report results. 

Cheers!

[Dale Tanski]

There is this phenonoma known as "stainless galling" which as you may imagine happens with stainless fasteners.  I have seen two freely moving fasteners (nut & screw) stop and lock solid, some even while in the hand tight stage.  I used to work for a company that manufactured stainless pressure fittings that contained threads and SS Galling was a reoccuring issue. I don't suspect that on your water fill cap it could ever occur as the class of thread is so loose by design, but you never know.  Once a thread galls its over, no amount of lube, heat, penitrant or force will fix the issue. 

SS Galling is why those closed body tubular turnbuckles (often found on smaller boats) are seldom used any more.  The stud threads are stanless and the bodies are stainless and at any given moment while in motion (while adjusting) they seize right up.  Most turnbuckles are stainless studs and chromed bronze bodies. The stainless and the bronze get along just fine.  I am sure you have had a fasterner or two lock right up and breaking or cutting them was the only way out. 

Dale