Fuel Tank Scum Woes

by Alex Joyce


Click here to download a pdf of this article, first published in the Auburn Heights Herald, Summer/Fall 2019.


Late summer 2018, one year ago, I went to check the fuel level in my 1910 Model 60, a car with its original copper tank as well as most of its original plumbing. Mike May and I had thoroughly cleaned the system in late spring 2017. To my dismay, the tank had green scum floating on the fuel, a 60-40 blend of diesel and gasoline. I learned that this has become common. After conversations with Don Bourdon, Howard Johnson, Charlie Johnson, and Mike May, I settled on Charlie Johnson’s approach. The following article goes through that remediation, its effectiveness, and the further steps that had to be taken in the spring of 2019, when the problem returned. I consider this final solution effective enough to communicate it to the steam car community.

Crude oil is now “cracked,” distilled, hard enough to create gasoline, kerosene, and diesel that are neither time- nor humidity-stable. In addition, the removal of most sulfur from diesel has had a particularly bad result for us. It was the sulfur in the fuel that prevented biological activity from readily starting. Gone are the days of finding a car with the tank ¾ full of good fuel after years of sitting in a barn. Equally gone are days when we can expect with certainty that fuel put in the tank in September of last year will be good come May, just eight months later. During those eight months of storage, even in a heated garage, the daily rise and fall of temperature and barometric pressure causes the tank to breathe in and out, letting the top surface of the fuel interact with changing air of varying humidity. The result can be to have biological activity start in the fuel. Once that biological activity starts, it spreads through the tank and into the fuel plumbing.

The common thought is that the fuel can be drained, the tank given some cursory and well meaning cleaning, and then one is free to refill, fire up, and steam away. If you are lucky, yes, but often, wrong. Several levels of pollution of your fuel system may have occurred. First, the fuel could be contaminated with biological growth; in addition, the fuel may have started to decompose, leaving a thick coating on the bottom and walls of the fuel tank. Second, the Stanley copper fuel tanks have baffles that create great hiding places for, to use baking terminology, “starters” to hide. Third, the inside top surface of the fuel tank may have biological activity on it. And fourth, if you have pumped fuel though your system before thoroughly cleaning, you have moved those biological “starters” into hundreds of hiding places. Among the obvious hiding places are threads in flare fittings, packing in hand valves, inside the two fuel pressure ballast tanks, the thin crevices within the fuel automatic where the automatic body halves clamp the diaphragm, the air line leading to the fuel pressure gauge, and so forth.


What to do?

There is mechanical cleaning, there is chemical cleaning, and there is biological cleaning. To do it right, all three is best, but certainly, you must do the first and last: mechanical and biological. Here is the account of what worked for me with a 16-gallon tank. Please scale up for larger tanks.


Mechanically Cleaning the Tank

You will need to remove your fuel tank, empty it, and scour the insides. Charlie Johnson developed a very effective method of doing this, which I have slightly modified. Supplies needed are old-fashioned lye-based drain cleaner, baking soda, plugs for the fuel outlet and bypass return, some sort of tumbler for the tank, and a water hose. Lye-based toilet cleaner is hard to find in many areas because many stores no longer stock it since it is an ingredient used in cooking methamphetamines. So call around before heading to your local hardware store.

Caution: Lye, when mixed with water, is going to make a very aggressive liquid that will burn skin and put out eyes. Before starting, put on a longsleeve shirt, long trousers, socks, and shoes. As you start, don safety goggles and rubber gloves.

One method of tumbling tank: jack up one drive wheel of tractor, step tank to wheel, idle in low-low. Photo, Alex Joyce.

Put about a pound of powdered lye cleaner into your empty tank, add about three gallons of water, and tumble the tank for an hour, making sure that the inside surface of every one of the 6 panels, all 8 corners, and all faces of every inside baffle get repeatedly sloshed and immersed in the lye solution—over and over and over, with the solution hitting all spaces from all possible directions. Remember that there are internal baffles and braces that you cannot see. You have to be very clever to ensure that the lye gets into each and every passage multiple times.

Drain the mess (and it will truly be a mess). Immediately flush with fresh water while tumbling for about five minutes and let drain. Following that, pour a pound of baking soda into the tank and add two gallons of fresh water and do the same tumbling as above to neutralize the lye. Then flush out, and if in the heat of summer, place the tank on black asphalt so the sun’s heat will cook the tank dry. You need it to be dry. After thoroughly dry, reinstall the tank.

Now that the tank appears clean (the word appears was intentionally chosen), how do you clean the insides of the plumbing, valve packing, nooks, crannies, and fuel pressure bottles/tank? This is where you have to be creative and in the final step use some pretty intensive stuff: lacquer thinner. But first, let’s biologically clean the system.


Biologically Clean the System

In the fall of 2018, after cleaning the tank as above, I proceeded to pump 4 gallons of lacquer thinner through the system over and over again. I did this for two reasons: (1) to try to kill the biological activity within the system, and (2) to flush crud out of the system. After pumping and pumping, I would open the main firing valve and empty the system into a bucket hanging from the end of the vaporizer. I used a white bucket so that I could see any bits that might flow out. Lots and lots of black specks and flakes came out. I repressurized the fuel ballast bottles, hand pumped up to 120 psi (you should pump until you hear your automatic bypassing if you run with a different fuel pressure), pumped some more, letting the fuel automatic bypass through the system for a bit, and then opened the main fire valve, emptying the system again into the white bucket. It took over a dozen iterations of this before the lacquer thinner came out the vaporizer carrying no bits of crud. When this happened, I assumed I was finished. I refilled the tank with fresh fuel from a well-known service station and did a bit of September steaming. April of 2019, seven months later, I discovered even more biological growth in my tank than before. I was very disappointed.

I called Bill Kennedy, chief technical officer of the Silver Ghost Association, himself a steam man. Bill has done thorough research on fuel deterioration in tanks. His immediate reply was that the remnant of bio-growth in diesel and kerosene fuels is insidious in its ability to withstand pretty extreme chemical cleaning. It hides and survives. He said that we must follow mechanical cleaning with biological cleaning. I called Power Services Products, Inc of Weatherford Texas, a family-owned and operated company specializing in solving diesel contamination issues since 1956. Their applications engineer was most helpful and recommended using two products: Bio Kleen Diesel Fuel Biocide followed by Clear-Diesel Fuel & Tank Cleaner.

From left, in order of use: Bio Kleen Diesel Fuel Biocide (double dosage to approximately 1oz per 8 gallons fuel), Clear Diesel Fuel & Tank Cleaner (dosage at end of cleaning at 2 oz per 5 gallons fuel and at winter storage as per instructions on container), Lacquer Thinner.

The Bio Kleen Diesel Fuel Biocide cleans the system. In their words, “Bio Kleen Diesel Fuel Biocide kills microbes in diesel fuel. The dramatically reduced sulfur content in today’s cleaner burning fuels has created ideal opportunities for microbes to grow in fuel tanks. The first indication of microbial contamination is mucous-like accumulation. … The only way to get rid of microbial contamination is to kill the microbes with a biocide.” Biocide is what kills the microbes hiding in nooks & crannies (including behind the fuel tank baffles), in the valve packing, in the hand and power pumps, fuel automatic, etc.

After having mechanically cleaned the tank as above, fill your fuel tank to the brim with diesel, and dose it with the correct amount of Bio Kleen. Then hand pump through the system so that every inch of fuel tubing—bypass return, main firing valve through the steam automatic to the burner, the line up to the fuel pressure gauge, and the fuel pressure/ballast tanks—have had dosed fuel flow through them. You will need back off the flare nut where the air charging line enters the air-side fuel pressure/ballast tank and pump until fuel squirts out, then tighten that fitting. You will also want to back off on the fuel pressure gauge’s flare fitting on the boiler side of the firewall and watch for fuel to flow out here. Only then will you have successfully flushed the whole fuel system.

Leave the fuel pressure gauge’s flare fitting a touch loose. Now let the car sit, full of the dosed fuel in the system, for 36 hours. It will be a good idea sometime during these 36 hours to hand pump fuel into the system and open the main fire valve to move the fuel through the system a second time. With no air cushion in the fuel ballast tank, pump super slowly while watching the fuel pressure gauge. Why? Each stroke of the hand pump is now fully felt by the bourdon tube within the fuel pressure gauge as the fuel tries to immediately pass through the fuel automatic with no air cushion to absorb the surge of pressure. You can peg your fuel pressure gauge and ruin its calibration.

After the 36 hours, drain this fuel and use it in your tractor, diesel truck, etc.


Chemically Clean the System

You have now done a lot of hand pumping, flowing a lot of fluid through the system. Without realizing it, you have broken free bits and pieces of crud and flecks of grit. Let’s get that all out and have a squeaky clean system from end to end.

Pour three gallons of lacquer thinner into your empty fuel tank. With lacquer thinner, you have to hand pump with very slow strokes or the system may become air bound as lacquer thinner has a very low vapor pressure. It is easy to suck too hard and fast on the “draw the fuel into the pump” stroke.

Crud flushed out with first lacquer thinner flush. Photo, Alex Joyce.

Loosen again the flare nut on your fuel pressure gauge. Put a bucket under the firewall and hand pump until the lacquer thinner flows out at the gauge. Tighten that flare nut, but not crazy tight. Loosen the flare nut where the air charging line enters the fuel ballast tank and pump more until fuel comes out here. Now the ballast tanks are absolutely full. Let it sit for a few hours. Be careful not to tighten the ballast tank flare nut and pump anymore! Why? As above, each stroke of the hand pump would have to immediately pass through the fuel automatic as there is now no air cushion to absorb the surge of pressure. You don’t want to peg your fuel pressure gauge and ruin its calibration.

After several hours, tighten the air to fuel ballast tank flare nut, open the main firing valve and with an air pump, as if you were charging the fuel ballast tank, pump air in until you have forced out a quart or so of liquid through the vaporizer into your white bucket left hanging on the burner branch fork. Then shut your main firing valve, and with the air pump, pressurize the system to 60 to 80 psi. Now your plumbing is full of lacquer thinner, and your ballast tanks are properly charged with air. You can begin to hand pump the system, flushing out crud released by all the activity you have been doing. Hand pump up to 120 psi, and continue pumping to flow thinner through the bypass system and back into the main fuel tank. Now open the main firing valve, and flow thinner through the vaporizer down to 70 psi on the gauge. Close the main firing valve, pump back up to 120 psi and a few strokes more, open main firing valve until pressure drops to 70 psi. Repeat and repeat until you flow thinner out through the vaporizer with no crud or specs of carbon. Now your system is not only free of bio-activity traces, it is truly clean and free of crud too.

Use aluminum foil to protect paint and to form a “spout” to direct the outflow from vaporizer. You may want to set the bucket on a block to place it closer to the outflow. Photo, Alex Joyce.


Finishing Up

Drain all the lacquer thinner and loosen the flare nut at your fuel pressure gauge and make sure it is free of lacquer thinner. To double check this, you can pump some air through the air charging valve, which will force any thinner out. Retighten that flare nut. Fuel up and add about 20% under the specified requisite amount of Clear-Diesel Fuel & Tank Cleaner.

Note: After cleaning the system, I found that the fuel automatic would bypass at seemingly random pressures. I removed the fuel automatic and disassembled it to find that fuel side of the diaphragm was nearly full of crud that had been freed by the above process. I cleaned, reassembled, reinstalled and adjusted to my desired fuel pressure, 120psi. It now works perfectly.



I did an experiment to verify that dosing the fuel with this is ok with our vaporizing fuel burners. I suspended a stainless steel crucible over three propane torch flames burning at full fuel flow. Into the crucible I poured 1/2 cup of fuel dosed with the Clear-Diesel Fuel & Tank Cleaner. The three torches created enough heat to completely boil the fuel away in 38 seconds. No residue was left. I repeated; no residue was left. I loaded up, trailered to Connecticut, and ran that tank of fuel through on the 2019 Litchfield Steam Car Tour. There was no carbon accumulation, and I never clogged a burner nozzle.


End of Steaming Season

Fill your fuel tank with your diesel and gasoline mix, dose with Clear-Diesel Fuel & Tank Cleaner, and hand pump a bit though the system with the system bypassing at full fuel pressure. Close your pressure-retaining valve and enjoy the winter. Happy steaming come next spring.

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