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Fuel Tank Contamination (for your information)

Seemann Member Posts: 11
I have an 1997 Hurricane Fundeck 196 configured for fishing.  It has a Mercury Mariner 125 hp 2 cycle outboard engine, probably 1989 or 1990.  I bought this rig in 2018 and I am still making repairs.  The first problem I encountered was hard starting, rough idling, and stalling when shifting gears.  It got to the point that it wouldn't start.  The problem was a contaminated onboard fuel tank. Apparently there was abrasive metal particles, and non metallic particles mixed with the gas in the tank.  These particles actually cut through the gas filter/watertrap, and engine mounted gas line filter, and deposited in the four carburetor fuel bowls blocking the needle valves.  A thorough cleaning of the carbs, and replacement of the filters resolved the problem. 
I am no longer using the onboard fuel tank because it would be a nightmare to clean, and almost impossible to replace.   This presents another problem, however.  I purchased two portable 6 gallon plastic fuel tanks at Walmart, and a new supply hose.  The Attwood hose connection did not fit properly so I replaced it with the original Mercury hose end.  I ran the engine successfully until the end of last season.  After a few weeks I tried to start the engine, but it quit after a few seconds.  I tried repeatedly to start the engine without success, and eventually caused blue, then dense white smoke to appear in the exhaust.  I was obviously injecting oil into the crankcase, but no gas.  Maybe there was some condensation as well.
The cap vent on my portable tank was open, however, my tank was obviously bulged by the warm temperature and sun.  I believe pressure in the tank forced fuel into the engine fuel line and fuel pump causing the pump diaphragms to expand, or rupture, thus not delivering fuel to the engine.  The engine is currently being repaired so I can't give you the answer to this problem, but I will at a later date.
I hope that these experiences will be of some help to those of you with older engines, and portable tanks.  I suggest disconnecting the gas supply hose to prevent the possibility of fuel pump damage.  I still need to find out why my portable tanks are not venting properly.


  • thurricane
    thurricane Administrator Posts: 389 admin
    Thanks for sharing this information - let us know if you figure out the venting on the portable tanks
  • Seemann
    Seemann Member Posts: 11
    I just got my boat/engine back yesterday.  According to the mechanic trash, and grit from the fuel caused two needle valves to remain open allowing too much gas (like full choke all the time).  In addition, there was rust inside the carburetors that caused another needle valve to fail.  I speculated on water in the tank due to condensation, and I was correct.  I purchase my unleaded/no ethanol gas from two service stations.  I never saw any contamination in the fuel, but I guess I'll have to pre-filter my fuel before transferring gas from my "Fill" tanks to my portable 6 gallon tanks that are connected to my engine.
    My speculation about the fuel pump being damaged was incorrect.  The pressure is fine, although the mechanic did note that my portable tank caps did not vent properly.  I have two "Neptune" 6 gallon plastic tanks that I purchased in Walmart.  I intend to email the manufacturer to find out how to remedy the venting process.
    When I abandoned my contaminated onboard gas tank, and switched to the portable tanks I purchased an Attwood hose kit for the Mariner engine at Walmarts.  Recently, I had a discussion with a charter boat captain about my starting problems, and he stated that he heard that Attwood fuel lines tend to deteriorate after use.  I cannot verify that statement, nor do I wish to malign the Attwood company that has many fine products out there, but I would really like to know if there is any substance to that statement.  As a precaution I am going to discontinue the use of that hose, substituting 5/16" gas line hose from Advance Auto, and connect the siphon bulb in between.
    This is my second experience with fuel contamination, and I hope to prevent it from happening again.  I use Sea Foam with every tank, yet I had some gummy residue in the carbs.  I'll try adding Stabil to my "Fill" tanks to avoid sour fuel.  I will be adding a fuel filter/water trap in my new fuel line as well.  I would appreciate any suggestions.