How to remove old gas from main tank of my 1989 I/O


Seaman Apprentice
Aug 29, 2007
I now took possession of a 1989 wellcraft 19 foot, open bow, with I/O. Seller told me, The gas is about 5 years old, but was treated every year with stabilizer and the tank was kept full. The fuel smells a bit like gasoline, but not like fresh gasoline. I would like to remove the old fuel as there is no room for adding some fresh. I tried a hand operated method of siphoning out threw the fuel hose that leads to the water separator but that did not work at all. I tried attaching a 12 volt low pressure fuel pump to that same hose, and fuel only dribbled out. I blew air from my air compressure back threw that same hose, and I could hear gurgoling in the tank , and I assume that is a good indicator. The engine has a mechanical fuel pump. What tips, suggestions have you that will work ?


Supreme Mariner
May 24, 2004
I cheated. I went to my dealer, and borrowed the device they use when prepping Boats for Storage, It was just an Electric Fuel Pump, with a couple of Hoses with barbs. I unhooked the Fuel line just prior to the Engines Fuel Pump, connected the Dealers thingy, put the other end in one of my cars and drained the Boats tank. Of course I borrowed it as they closed on the Saturday and was waiting in the Parking lot for them to open Monday Morning . YMMV

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Jul 23, 2011
5 year old fuel is no longer fuel.

you will most likely need to pull the sender and may have to mechanically clean the tank.

Here is what I have done in the past
simple cleaning - 2 gallons of simple green, followed by 2 gallons of boiling hot water, go for a drive down a back country gravel road at 40mph - drain
removal of fuel deposits - 3-4 gallons of denatured alcohol followed by the drive down a back country gravel road at 40mph
repeat as required to get fuel tank clean

your anti-siphon valve is most likely stuck

there is also a filter in the pickup tube. that is most likely plugged