Sunday, June 7, 2015

Are We the Cause of Fuel Breakdown?

It has long been known that copper and zinc are very bad for fuel stability (gasoline and diesel). The use of these materials is banned by good practice, ASTM standards, fuel producer and engine manufacturer guidance.


ASTM D975 Appendix X2.7.2: Fuel Storage Conditions
Copper and copper-containing alloys should be avoided. Copper can promote fuel degradation and may produce mercaptide gels. Zinc coatings can react with water or organic acids to form gels which rapidly clog filters.

Cat installation guidance.

Material. Black iron pipe is best suited for diesel fuel lines. Steel or cast iron valves and fittings are preferred.
CAUTION: Copper and zinc, either in the form of plating or as a major alloying component, should not be used with diesel fuels. Zinc is unstable in the presence of sulfur, particularly if moisture is present in the fuel. The sludge formed by chemical action is extremely harmful to the engine’s internal components.

Cummins installation guidance.

Diesel Fuel Piping. Diesel fuel lines should be constructed from black iron pipe. Cast iron and aluminum pipe and fittings must not be used because they are porous and can leak fuel. Galvanized fuel lines, fittings, and tanks must not be used because the galvanized coating is attacked by the sulfuric acid that forms when the sulfur in the fuel combines with tank condensate, resulting in debris that can clog fuel pumps and filters. Copper lines should not be used because fuel polymerizes (thickens) in copper tubing during long periods of disuse and can clog fuel injectors. Also, copper lines are less rugged than black iron, and thus more susceptible to damage.
Note: Never use galvanized or copper fuel lines, fittings or fuel tanks. Condensation in the tank and lines combines with the sulfur in the diesel fuel to produce sulfuric acid. The molecular structure of the copper or galvanized lines or tanks reacts with the acid
and contaminates the fuel.

 Yanmar manual
piping is specified as rubber or steel (page 9).

1.5 gallons of diesel were left for 4 months in a clean closed but vented bucket. The metals samples and water drawn from the atmosphere combined to destroy the fuel. Interesting.


And yet West Marine and Defender Marine continue to sell brass and copper parts for fuel systems and we continue to buy them! Simply put, they are greedy and we are stupid.

What can we do, short of ripping out plumbing and installing hose, aluminum, and steel?

The best patch is a good corrosion inhibitor (Practical Sailor August 2012 for gasoline, Practical Sailor August 2013 for diesel) that will prevent corrosion (without corrosion the ions will not be present in the fuel) and sequester those that may already be present (from the refining and distribution process, or from the corrosion that has already taken place in your boat). Just a few ppm of free ions will dramatically accelerate fuel degradation.


Amazing, what we should be told... but are not.


  1. Yep, new tank by PO has brass fittings where hoses connect. I assume stainless steel replacements would be a good idea?

    BTW, nice blog ;-)

  2. I'm not sure I would sweat a few fittings. It is copper tubing I would avoid.

    My greater concern would be galvanic corrosion. For certain, you do NOT want brass with an aluminum tank.