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Author Topic:   gas tank sludge
dshiv posted 07-01-2005 05:25 PM ET (US)   Profile for dshiv   Send Email to dshiv  
The '89 Outrage 22 Cuddy I inherited was parked for 6 years on it's trailer with 1/2 tank full of gas. All the fuel has been evacuated, however, there is 1-2 inches of "sludge" in the bottom of the 77 gallon tank from the gas sitting for so long. My question is, how do I get rid of it? I've tried some different solutions to break it down but nothing is working. Anyone have any thoughts??
colowhale posted 07-02-2005 01:07 AM ET (US)     Profile for colowhale  Send Email to colowhale     
Is your tank removable? I just cleaned my 24 gallon Paye tank out as best I can. I'm no expert but I believe the sludge in my tank was varnish. I had flakes floating around in the gas. Determining that the gas was bad, I syphoned it into a portable tank and dumped it in my car. I removed the fuel pickup as well. I then took a bottle of Sea Foam and dumped it in and let it sit for a while. Later I put a 5 foot piece of heavy chain in the tank and sloshed it around as much as I could (I have a 24 gallon Pate, so if yours is removable you may be able to do the same with another person) to loosen the coating on the inside. I then dumped this into a container after letting it sit overnight. Got the hose out and blasted the inside as best I could, and rinsed out the flakes several times. Since I do not have an air compressor I taped my shop vac hose to the tank and sucked air through the fuel pickup hole to help dry it out. It was bone dry in the morning. But the air here in Colorado is pretty dry. I read in another post that you may also put alcohol in the tank to help it dry.
RocketMan posted 07-02-2005 07:51 AM ET (US)     Profile for RocketMan  Send Email to RocketMan     
I have never done this, but I like to do this kind of stuff. I wouldn't mess with it chemically, not at first anyway.

One thought is a 'venturi'. If you have a 'shop air' source, you could hook up a venturi that can be used to suck the sludge out into a bucket and take it to the local waste disposal. That would get the majority of it out.

Another thought is, will the stuff float on water? Chances are decent it will if it isn't bonded to the tank bottom. If so, flow clean water into the tank until the "sludge" floats up to the top. Not sure what you're dealing with at that point, but maybe float it out altogether or scoop it out.

andrewbanks posted 07-02-2005 07:15 PM ET (US)     Profile for andrewbanks  Send Email to andrewbanks     
Florida Marine Tanks, Inc. (305) 620-9030 I had the same problem with my outrage. $700 bucks for a new tank, but an least you'll have piece of mind. Andy
Baseline posted 07-13-2005 09:36 AM ET (US)     Profile for Baseline  Send Email to Baseline     
I had a similar problem with my Montauk Tank, which is 24 gallon. I had a ½ inch of gum and varnish in the tank when I got the boat. The tank was also stained from the two cycle oil and the sight gauge looked like it always had a ½ tank of fuel.

Over a few weeks I tried everything I could think of and nothing worked; Acetone, Gum Out, Xylene, Mineral Spirits and several other solvents. Most of the solvents were in the tank for a few days and came out as clear they were when I put them in the tank. I had a bottle of MARINE-CLEAN™ used to prepare and degrease metal for painting, for some reason I sprayed a little on the sight gauge and it began to remove the stain instantly. I was a little apprehensive of using Marine Clean, since it’s a water based cleaner. I did not want to be putting water in my fuel system. But once I saw the results it was a non-issue, since nothing else I tried made any difference.


Marine Clean will dissolve the junk in your tank, without hurting it. It will take a few days for it to work through an inch of gum, but it will work. In my case it came perfectly clean in just three days. For your size of tank I would start with 5 gallons of Marine Clean and 1 gallon of hot water. Let the product sit for in the tank for at least a week. You’ll need to agitate the solution every so often over the course of a few days. Driving the boat around the block on a trailer a few times during the week, making harder than normal starts and stops, should get things mixed up pretty good.

Before draining the tank of the cleaner, fill the tank with water to help clean the sides of the tank. Let it sit for a day or two.

You’ll have to drain the cleaner out of the tank and rinse it with water. I drained the tank and filled it with water and drained it several times. If the tank is still not completely clean after a week, I would repeat the entire process again. It took years to develop the varnish and gum it might take a few weeks to get rid of it.

Once the tank is completely clean and drained of the rinse water, go to the Auto Parts store and get a dozen bottles of dry gas. There are two types of alcohol used in dry gas; Methyl or Isopropyl, you want the Dry Gas that has Isopropyl alcohol not Methyl. The Isopropyl alcohol will absorb the residual water in the tank, Methyl displaces water but doesn’t absorb water. With the Isopropyl alcohol in the tank; drive around the block to agitate the tank. Drain the Isopropyl alcohol from the tank and the water will be removed with the alcohol.

Marine Clean is great to have a round the house, I use it for most cleaning tasks. Its one of the fastest and best brake dust removers I ever seen for wheels.

Good luck,

dshiv posted 07-16-2005 10:43 PM ET (US)     Profile for dshiv  Send Email to dshiv     
I took the boat to a friend who is in the boat business. Luckly, he has experienced this before. He is breaking the "sludge" down chemically which seems to be working. He has an electronic pump (which I don't) to remove everything. He's using the dry gas method too. Thanks again to all for the great info.

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