How to replace corroded sender unit

[TJS]

The sender unit on my 2000 Osprey (19.5 ft) is very corroded and may be the cause of water getting into my fuel. The attached picture shows only two screws that have a possibility of removing. The other screws need to be ground down. I have to hope that studs will be removable from the flange once the sender is removed to enable replacement unit to be installed. My mechanic has warned me that if screws can not be removed then the only option would be to replace the fuel tank. The deck would need to be cut to replace the tank which doesn't make sense for the value of the boat. Any suggestions?

[GoneFission]

The pic did not come through, but your situation is not unusual.     The best shot you've got might be to hit it with PB Blaster, let it set overnight, then try to remove the screws with a 6-point socket and an impact driver.  A 12 point socket will usually round the corners off on the screws, and a regular screwdriver usually won't work when the screws are corroded.  Hopefully the screws will come loose.  Replace them with new, quality stainless screws.  Always check replacement screws with a magnet - it a magnet picks them up - don't use them.  There is some junk sold these days as stainless, and good quality stainless (304, 316, and 321) is all non-magnetic.   

[Tim S.]

I wish there was hope for removing all the screws but that's not the case. I posted the picture n the gallery (sender). I think my only chance is grinding the top of the screws off. Do you think I'll be able to secure the sender to the tank by taping new holes into the flange or using a marine adhesive? I don't like the sound of it but this a last ditch effort and may be part of the decision to keep the boat or sell.

Mod Edit:

[Capt. Bob]

Is that a poly tank?

[Tim S.]

Yes. It's a poly tank (40 gal).

[Woodeneye]

Yikes.

Might be easier to replace the tank? I was going to suggest ATF & Acetone 50/50 (Hillbilly PB Blaster and about 2x more effective) but I'm not sure if Acetone would damage the poly? If its ok for gas it'll probably be ok for Acetone.

Grinding the heads of the screws may melt the poly too, so perhaps grind a bit at a time and wet it down?. Selling the boat because of a recalcitrant sender seems OTT? Is it the straw that broke the.....

[Capt. Bob]

Some thoughts.

http://classicaquasport.com/smf/index.php?topic=9912.0

http://classicaquasport.com/smf/index.php?topic=11163.msg109979#msg109979

His "looked better" than yours:


But during removal:


Good luck.

[wingtime]

#1 rule... TAKE YOUR TIME.

Hit it with PB blaster (good) or ATF & Acetone mix (better), or Kroil (best) and let it soak overnight.  Try a impact driver (the kind you hold in your hand and hit) to remove the screws with the heads still on them.  Again... Take your time!  vacuum up all the rust and bits so they don't end up in the tank.  Be very careful grinding... sparks and fuel vapors are a bad mix.  Hopefully you can get it off and extract the studs.  If not you can file them flush and drill use a easy out... or drill them out and tap... or drill new holes and tap those..  A new tank is a last resort option.

Oh and spray the new one down with corrosion X or something once you get it back together.

[CTsalt12]

Yikes I do not envy you with that job.  I think it would be easier to chisel around the screw hole and basically chip away the whole sender, then use a vise grip to twist the screws out of the tank and not the sender.