[C320-list] C320 Fuel Tank Replacement/Repair

[Dave and Ev]

My Catalina 320 is a 1999, with a 15 year old original fuel tank. I had 
an issue with my fuel tank causing a nuisance leak which involved the 
gasket on the sender unit on top of the fuel tank. When I found the 
nuisance diesel in the bilge,  I discovered that one of the screws was 
loose and caused a nuisance drip. Tightening the five screws on top of 
the tank was the easy part. Cleaning the diesel from all the secret 
passages in the bilge took the most time. As outlined by other 
contributors, the cleanup is complicated as described in the article and 
it involved me removing the aft water tank to get all of the diesel 
cleaned up. Lots of simple green did the trick. I was concerned about 
the tank, being 15 years old. I pumped the remaining fuel from the tank. 
I then removed it from the boat through the hatch into the aft cabin. I 
used kerosene to loosen up the black biomass inside  (most likely 
microbial mat) and cleaned out the tank to the best of my ability 
without cutting any access holes. Lots of shaking and several doses of 
kerosene removed lots of the residue. The internal baffle makes it 
challenging to access all the parts of the tank with one access port. I 
did not want to add any additional potential weeping spots, so just 
worked with the existing penetrations. While the tank was out, I scuff 
sanded and coated the external surfaces of the tank with thiokol, which 
is used to fix diesel weeps on tanks in the industry. While other owners 
reported weeps in the welds, I decided to coat the entire tank just in 
case. The work of taking it out was the same and it was done. In the 
meantime, I purchased a small piece of 20 mil HDPE plastic pond liner 
for about $35 from Amazon. HDPE is used as secondary containment for 
diesel fuel storage. I installed the HDPE beneath the tank when I 
reinstalled it so if any drips or leaks ever do happen again they cannot 
pass through the bilge but would be fully contained in the HDPE plastic. 
I considered replacing the tank, but it had no known leaks. This was all 
preventive work and for around $120.00 I have a tank installation that I 
hope will provide years of trouble free service. Jeff Hare has done an 
excellent job in outlining the issues with the aging fuel tanks. Perhaps 
at some point in the future I would consider the larger tank, but this 
will do fine for now.
Dave Cushman
It Tips  #628