Cleaning a gas tank.

[KRH1326]

Ok Guys,

I have a 62 gal. aluminum belly tank, that is not easily accessible. The tank's integrity itself is AOK, but I think I have a load of crud in it.
BTW, it is my 1976 OMC 235HP (351W) w/ holley 4 bbl list 7163.
I have been battling with a fuel delivery issue coupled with a non professional carb rebuild. This is due to the boat being a restoration project, not just a maint and repair issue.
The symptoms have been starts out running fine and smooth, then, after running for a good long while, the longer it runs, the crappier it runs.
I followed the steps in the adults only section to trace boat side system. I did take it a few steps further, tho. I am using an electric fuel pump right now for diagnostics. I installed a compound guage right at pump disharge, another at pump inlet and one at the antisiphon valve at tank.
I start up with 7 PSI (supposed to 7-9). Let it idle for a while, still 7 psi to carb, close to 1" hg at pump inlet close to 1" hg at tank. There is a brand new Sierra fuel/water filter between tank and pump. Also installed clear glass filter at pump inlet.
Have to run for 10-20 mins no wake, to clear the harbor. Still good. Jump out and plane off, AOK.
Run for 20-30 mins, engine starts losing power. Quick check guages while running- pump pressure dropping, hg rising.
This fuel pump is brand new, but I am suspect of the quality of strength. It does not like to pull up a hard vacuum, builds one up slow.
Finally engine power falls off and stalls. Guage at carb reading vacuum, guages at pump inlet and at tank reading 8-9" hg.
I spun the 90 and ASV off the tank, and found a screen, right up at top of tank. Pulled the screen and found good amount of crud. Cleared the debris, and looked further. There is a dip tube running down into tank, that I have not been able to remove for inspection. The screen sits into this. The tube seems to be part of the fitting that is tig welded into tank top.
OK have to clean the tank. Besides this 1/4" port, and the fill and vent ports, the only other thing I have is in the center of tank, sending unit. The opening, after removing to unit is approx 1-1/2" - 2".

HOW DO YOU CLEAN A TANK? I am mechanically adept. Yes run out as much as possible, till engine can't suck anymore up the tube, but then what?

I wanted to run this idea past a few of you guru's before I start wasting my time, if there is a better way. I am contemplating removing the screen and the ASV ( for cleaning purposes only ) use the elect fuel pump to pull through a temp hose barb, the sierra filter, through the pump, but then temp discharge back into tank. Let it run all day,maybe the day after, keep changing the filters and watching the clear filter.

Short of ripping up the deck and removing the tank, is there an easier way? Or actually a better way?

Thank you for reading my novel, but I am trying to be as accurate as possible.

Ken

 

[JustJason]

Re: Cleaning a gas tank.

Thats a tough one if you can't pull the tank out of the boat or tip it upside down.
Couple of shade tree things you can try....

Pump out all the gas. Pump the tank full to the brim with water. Cut the tank open with a a jig saw then weld the aluminum plate back on.

Pump out all the gas, pour in 4 or 5 gallons of murimatic acid. Let it sit for a bit and then aggitate it the best you can. Pump in water and hope the loose stuff floats enough to come out the sender hole.

Pump out all the gas. Let the tank sit for a month and let whatever rust is on the bottom get good and dry and caked. Pour in 5 or so gallons of a thin epoxy to coat the crud on the bottom and hope you don't cover up your pick up tube. If ya do, no biggie, you could always plumb in another one.

Short of ripping out the tank there is not a whole lot you could do. I suppose you could pump it with water and cut the whole top off. Then fit the cavity with plastic tanks and 2 part foam them into place.
Or just keep a case of fuel filters on the boat.
Good luck.

 

[HT32BSX115]

Re: Cleaning a gas tank.

Cut the tank open with a a jig saw then weld the aluminum plate back on.

BOOM!!

HOW DO YOU CLEAN A TANK? I am mechanically adept. Yes run out as much as possible, till engine can't suck anymore up the tube, but then what?

You said the tank was accessible...

Leave some gas in the tank 15-25 gallons or so....

Remove the fuel pick-up tube(it has a screen on the end)

Remove the gage sender and obtain some 3/4-1 inch clear vinyl hose long enough to reach out of the tank to the ground and about 8ft more. (Home Depot and Lowes has it in rolls)

Depending on where the sender is (usually towards the rear of the tank) Tip the tank up (bow up) opposite the sender hole. (Depending on how full the tank is you might want to pull the sender with the tank LEVEL first... to see how high the bow can go without fuel boiling out of the hole!!!! or you will have gas everywhere when you tip the bow up!!

Fill the hose with fuel (I.E. start a siphon) and use it to vacuum the fuel (and all the debris, sediment and water) out of the tank. Have a helper outside ready to switch collection tanks so you don't have to stop every time a container fills.

DO THIS OUTSIDE with plenty of ventilation and have a fire extinguisher handy. (no smoking)



Cheers,

Rick

 

[JustJason]

Re: Cleaning a gas tank.

No Boom if you purge the fumes with water first...

 

[HT32BSX115]

Re: Cleaning a gas tank.

Well, probably true.

It's just not required to cut a hole in the tank if you can get to the gage sender.

You can easily suck up all the contamination with a siphon hose.

I did it without even removing the tank.

 

[xxturbowesxx]

Re: Cleaning a gas tank.

Find a siphon pump from harbor freight that works off a cordless drill that way you shouldnt have to worry about sparks..

 

[jonesg]

Re: Cleaning a gas tank.

BOOM!!

well he did say fill the tank with water first ya know.

They sell 12x12 alum access panels with a gasket, pre-drilled, just cut the hatch opening and get in there. Seen the ads in the back of boating magazines.