what are the tanks made of? any idea if the tanks were full while it has been standing for that period of time? if they are mild steel
then chances are they may have rusted on the inside if they weren't full. i went through this a few years ago too. first thing i did was change all the filters (primary and secondary). then run it for an hour or so at the dock
. then take a look at the filters. if clean then try a little trip, something safe, so choose a calm day. then check the filters again. is it a full displacement hull
? any way you can rock the boat from side to side dockside to stir things up? if so, do it, then run the engine
, then check the filters again. the real test, of course, is to take her out in rough seas. make sure you take plenty of spare filters with you. if the engine(s) dies, switch to new filters (keep the old ones for inspection). you could have rust, diesel bug, dirt, water
, or any/all of the above. there are additives to remove the water, to kill the bug, and the filters should get the dirt and rust, but it could take time. you might also want to get the fuel
"polished". i've added additives for the bug and water, and after motoring for 50 hours or so in force 6/7 conditions, and making sure that i buy high quality (clean) diesel, the tanks, as evidenced by the filters, seem to be in good shape. i considered cutting them open and installing inspection holes, etc., but went the other way with good results, so maybe worth a try that way before cutting. my advice is to carry lots of spare filters, and know how to change them under way, at sea, in rough conditions.