How to clean a built in boat fuel tank?

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May 29, 2005
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Ozark Mountains
I have a 1998 Formula stern drive boat with a 106 gallon built in fuel tank. I bought it used a few years ago and the last owner had not used it in several years. The fuel tank would be almost impossible to remove.

The problem is particles built up in the tank. Every year I go through quit a few marine canister fuel filters, sometimes a couple in a day.
Does anyone know how to clean out the particles? There is no access to the tank except for a 1 1/2" access hole.

Also, the standard fuel filters have only a tiny filter in them with about 2/3rds of the can space left open to collect water. I can't find any larger filters??

Thanks in advance!
 
I would examine the particles first and make sure it isn't the tank disintegrating. Then you could maybe make a homebrew fuel polishing station to flow and filter and dump back into the tank.
 
I heard of a company years ago that would do Boat gas tank cleanings, like for what you have. I believe what they would do is pump out any old gas, and they used some type of cleaner they would pump in and out of the tank. I guess they would cut a hole in the top of the tank and inspect it for any form of debris. And use that hole, to suck the cleaning agent back out. Or maybe they just used the hole for the gas gauge. If it's a steel tank, I wouldn't waste the effort. But Aluminum or fiberglass doesn't corrode , so you should be good after it's cleaned.,,,
 
I agree you need to find out what the particles are? Rust? Varnish? Did kids dump something in the gas tank. Mean ex-wife who hates boats?

I would guess it's varnish.

If varnish then get several gallons of alcohol and pour it in the tank. If on a trailer take the boat & trailer for a ride every day for a week or two to slosh things around. Drain, flush with a few gallons of gas.
 
can you splice in a secondary fuel filter in the fuel line with much more capacity? I think it would be very difficult to flush this tank IMO.

Just my $0.02
 
You should not add any filter setup that is not USCG approved.

Companies have services that "polish" diesel fuel. Basically run the fuel from the tank through a filter and back to the tank for several hours.

But you need to figure out what the particles are. If they are from the gas tank rusting away or a one time issue where a contaminate got in the gas.
 
My suggestion of a 3/4-16 filter was based on cost, this was the cheapest way to filter…

Another way is a fuel filter with a clear bowl…

Yet another is Wix 33033, a 3/8 inline fuel filter (33032 is 5/16, 33031 is 1/4)
Look on Rock Auto for good prices…
 
I would examine the particles first and make sure it isn't the tank disintegrating. ....
Agree, something doesnt sound right here. I WOULD BE VERY CONCERNED about the tank itself. It shouldn't happen but I never researched how long these tanks should last. I assume plastic but maybe in a Formula aluminum (?) I dont think steel has been used in ages. I sometimes look at the plastic one built into the floor of my 2008 boat and wonder myself. I can only see the top front where the hoses come out.
 
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