What's best to clean a marine fuel tank?

[Hogtamer]

Reworking an old boat that had some gas in the fuel tank (aluminum) for a couple of years. Got the tank out and mostly empty but smells like old varnish. How to get the rest out and clean the tank?

[Winger Ed.]

I've had a couple like that.
What worked for me was to dump it, put a couple gallons of Lacquer thinner in it with a piece of chain, and shake/tumble it around.
Dump it, put in a couple gallons of gas, shake it around, and dump it.
Strain the lumps out of the gas, and do it again until there is no loose 'stuff' in there.

That'll work, but the smell won't come out.
Also, pull the supply tube out from inside the tank and make sure it isn't clogged.

If the tank can't be removed, use the same principal, but stick a rag in there and wipe it around as best you
can with a coat hanger or something and siphon the solvents & gas back out.

If you don't think ya got all the beasties, put a large capacity fuel filter ahead of the fuel pump and keep a eye on it.
Fuel pumps can pump through a semi-clogged filter with a lot more pressure than they can suck fuel through it.

It's a hassle, but way cheaper than replacing the tank.

I'd replace the fuel lines when ya do it.
And car fuel lines are different than marine use ones too.
Car fuel line will rot and crack sooner.

Edit-
Yeah. The 'old' stuff I get is usually so old & far gone, nobody else would fool with it.
The last fuel tank I cleaned was still half full from about 15 years before.

[Wisest.fool]

Define "OLD" some aluminum tanks have a kind of epoxy like liner. such as: https://www.eastwood.com/por15-fuel-...8aAr47EALw_wcB

I would simply flush with water and let it dry out over a couple days.

I recently rehabilitated a sunken 20 foot mako center console. there was a significant amount of water in the gas... obviously. i pumped it through a fuel water separator 3 times then fed that fuel to my truck. then i flushed the tank with water and sucked it back out with a wet dry vacuum. let it dry out a couple days and put fresh gas in. i didn't use any cleaners to prevent ruining any liner that may have been in there. worked for me.

[Brassduck]

do you have a pressure washer? I have cleaned many fuel tanks, trucks, riding lawn mowers, motor cycles, use a good soap wash out dump it do it again. several cycles and rinse with plain water and let dry. hot water works best. good luck !!!

[samari46]

Dawn dishwashing detergent is great for cleaning gas and oil spills.
I've used it to clean out 5 gallon gas cans all then foamy bubbles. Put about a gallon or two of water and add about two cups of dawn. Shake the heck out of it. Then dump it out. repeat as often as needed. And don't throw out the old blitz gas cans. You can still get nozzles for them or make your own. I did one as a test case. You wouldn't believe the crap that came out of the tank on the first wash. Ended up doing that one three times. No crap in it now.Clean up the outside get all the dirt and grime off it. In most cases almost looks like new.Depending how much old gas was in the can save it when you need to burn some trash. Frank

[Lloyd Smale]

varnish in a tank can be tough to get out. We had a motor cycle tank that was on a bike we found in the woods and were restoring. It was BAD! What we did was dump a whole can of sea foam and filled the tank with mineral spirits and let it soak for about a week shaking it good a couple times a day. that was a 2 gallon tank so it would take quite a bit of sea foam but it came out looking about like new. I guess to save money you could fill it half way and try kerosene instead of the mineral spirits and shake it and turn it upside down every other day and do it for a couple weeks.

[BeeMan]

A gallon of E-85 gasoline cleaned up a varnished fuel tank on an old truck my son bought. It's a bit ironic that ethanol in gas causes problems but it did a great job of dissolving the crud when straight gas and petroleum solvents didn't work.

[Froogal]

A gallon of E-85 gasoline cleaned up a varnished fuel tank on an old truck my son bought. It's a bit ironic that ethanol in gas causes problems but it did a great job of dissolving the crud when straight gas and petroleum solvents didn't work.

Yes. E85 will do the trick. I could argue with you about ethanol causing problems, but this is not the place.

[jimlj]

I don't know about an aluminum tank, but I cleaned a plastic snowmobile tank with about a gallon of carburetor cleaner. It got rid of all the sludge and varnish. Carburetors are made from aluminum so I don't think it would hurt the tank, but like a carburetor don't leave it soaking for longer than the instructions call for.

[Hogtamer]

Turned out to be easy as the inside was bright and shiney! Loaded it up with dawn detergent and ran water through it until it ran clear. Rinsed out several more times and now drying upside down. Thanks for the input!