A warning and a request for help.
We have started some work on our 1969 18' H&M classic. The plan is to rebuild the 302 and that is underway (stroke to 331, GT-40 heads, keeping the H&M externals). Our goal is to have the boat look exactly as it did when it left the factory in 1969 (it is already in awesome condition). We already took care of some (typical for a 46 yr old boat) transom and stringer glass/coring issues. Rewiring the entire boat, painting drive, etc. etc. etc. etc. We decided not to remove the deck and change the tank for many reasons. However we just discovered something, we have not used the boat in over 10 years, it has been covered and indoors, but we left gas in the tank. When we went to pump out the tank yesterday we discovered a thick coating of a varnish like substance on the tank bottom (removed the sending unit for visual access). Also the gas pick up is seemingly plugged with this substance as we cannot blow any air into the tank from gas line back in the engine area -- it seems to be solidly plugged. This substance is thick tough and difficult to remove. So based on this:
1) the warning, we really screwed up leaving gas in the tank, if a boat is going to sit around for years (actually we never thought it would go unused for so long but it did) you have to remove the gasoline from the tank(s). I am not sure how much was in there and how much evaporated but we removed the liquid in the tank and it was only a couple of gallons --with much residue left behind.
2) the request for help: does anyone have any idea what we can do to recover from this blunder? Short of removing the deck and changing the tank. We dug some of this gunk out of the tank and experimented with it. Diesel fuel doesn't seem to effect it. Gasoline does little to effect it. Acetone seems to effect it slightly. MEK seems to have the biggest effect on it and will dissolve chuncks of it. Hot water seems to soften it but not completely dissolve it (only tried for 10 minutes or so). Vinegar (based on a suggestion found on the internet) seems to have little or no effect. I haven't tried carb cleaning solution.
I guess we could try dumping several gallons of MEK in the tank and letting it sit for a few days and then try pumping it out. Nasty and dangerous stuff to work with but it seems to dissolve the gunk. However I don't know if it will have enough access to the solidified varnish in the gas line pickup to be able to clear that. We would love to find a feasible and safe way to clean out this tank without changing it. You all know where this tank is and how it is difficult to access. Any ideas? Thanks very much in advance. Ed
1967 Triple Hatch 18' (sold)
1969 Holman&Moody 18 2+3
1982 454 TRS no windshield 22 2+3 (sold I'm an idiot)
1997 454/Bravo 1 22 2+3
+ some less cool, more functional boats