Contaminated Diesel (Algae?) - solutions and prevention

[Nekton73]

A fellow boater is having some trouble with his fuel system and I wonder if I could prevail upon the collective wisdom here to recommend solutions. The boat is a Catalina 34 (early 2000’s I think) with the M35 engine. Usage since purchase 3 years ago has been seasonal spring-fall with regular sailing every week, most weekends, and several longer trips each season. Boat laid up each fall with nothing special done to the fuel system (that I know of) other than adding Biobor JF diesel biocide. So far no troubles… until this season.

This season the boat did not see much use and has sat for longer periods between outings. This week, during a ‘pre-flight’ check while getting ready for a weekend trip, a lot of sludge was observed in the bottom of the fuel filter (pic attached). The engine was not started, and had not been started for about a month prior to this finding. No contamination was observed earlier this season as far as I know. Removal of the filter showed the growth at the mating surface as well. Suspicion is the entire system and tank is full of this stuff, but no further searching has been done.

Current plan is to purchase a small day-tank, fill with clean diesel and plumb it in just before the lift pump, change the filters, and then run as is for the weekend with trip back ending at the storage facility ready for haul-out next week.

A few questions we have:

- will starting the engine with contaminated lines damage the fuel or injection pumps, or injectors?
- if starting the engine is not recommended, what decontamination methods should be used before it can be started?
- if it’s ok to run the engine off a clean tank and filters until end of season, what steps should be taken for full decontamination of the fuel system before next season?

Thanks for any info or suggestions.

[Lepke]

I've started many marine diesels that sat for years, as long as 20 years. I don't think you need another tank. Kill the algae first and carry extra fuel filters. The fuel in the lines should be fine. There are several products for keeping diesel fresh and killing the organisms that can thrive in diesel tanks. Usually a triple dose kills the algae, then the filter catches the debris before your engine.

I use diesel additives every fueling. It stabilizes the diesel for up to a year, has a higher cetane rating (better combustion/better mileage), kills bugs, lubes injectors and injector pump, etc. I use Archoil products, read about them here: archoil.com
Available at archoil, Amazon, or ebay.

[Kettlewell]

I agree that I would run the engine and just have several filters handy in case one plugs. I have been amazed how clean my on-engine filter remains after the fuel passes through a 10-micron Racor filter.

[thinwater]

Originally Posted by Kettlewell

I agree that I would run the engine and just have several filters handy in case one plugs. I have been amazed how clean my on-engine filter remains after the fuel passes through a 10-micron Racor filter.

Another possibility is that the bugs are resistant to Biobor. Like bacteria, different strains respond to different antibiotics. I would try Raycor Diesel Biocide, which uses a completely different, also well proven, biocide chemistry.


https://www.practical-sailor.com/boa...ated-boat-fuel


I have tested many biocides and used them in industry. Raycor and Biobor are two of the best, but they work differently.

[Nekton73]

Thanks for these quick replies folks, I will pass them on. Any additional insights, please keep them coming.

[Nekton73]

And a follow up pic of the filter feed, blech.





He is going with the day tank and clean fuel just to avoid any problems this weekend, but comforting to know the consensus is not to worry about running the engine with the small amount of contamination in the lines.
The point about the bacteria being resistant to Biobor is interesting. He will purchase what is available locally for a (hopefully) quick solution and also look into the other products mentioned.

[CarlF]

While he can certainly go with his day tank idea, the sooner he kills the algae in the main tank the better. Then have the fuel pumped out and cleaned or disposed of. Otherwise it will keep growing over the winter and stick to the tank walls making it harder and harder to clean the tank without cutting a hole in the tank top to allow cleaning tools to be inserted.

Like running aground, most long time cruisers have had a case of diesel bug (after which they religiously use a biocide to never go through it again). The tried and true solution is to add biocide and then run the fuel through the filter by using the engine. No damage is done to the engine, you just have to keep changing filters until the bug is gone.

Also, have him check the rubber o-ring at the tank fill. These get old and leak over time — allowing rainwater to get in the tank. This water often causes the diesel bug. If the o-ring is over 10 years old, replace it.

[Ballsnall]

Originally Posted by CarlF

This water often causes the diesel bug.

This is true, your friend doesn't have a bug problem, he has a water problem.

[boatpoker]

Algae cannot form in diesel fuel tanks as it needs photosynthesis to survive and propagate. The Algae-X people created a snake oil business with this mythology. There are various bacteria than can form but not algae.

Somewhere over 24,000hrs. under power in my log now and have never added anything to my diesel fuel. Additives are already added at each refinery. Since I am not a chemist I would not try to out guess the refinery as to what other chemicals additives are advisable or even necessary.

[Nekton73]

Again great info, thanks.

Tank will be removed over winter, access hole cut, cleaned properly, and re-sealed with an inspection port.
Alternate biocide will be implemented going forward, perhaps switching between two to avoid bacteria resistance.
Water problem will be addressed also.

[boatpoker]

Originally Posted by Nekton73

Again great info, thanks.

Tank will be removed over winter, access hole cut, cleaned properly, and re-sealed with an inspection port.
Alternate biocide will be implemented going forward, perhaps switching between two to avoid bacteria resistance.
Water problem will be addressed also.

As long as you are going as far as removing the tanks may I suggest a modification ...

The common tank has a pickup tube reaching down to 1/2" to 1" from the bottom of the tank. Some of that 1" or so will inevitably be water. Sitting water is not only the main cause of corrosion (or rust) of metal tanks but the interface of water and diesel fuel is the bacterial breeding ground.

We had our tanks built with bottom fuel feeds. No water ever sits in the bottom of our tanks, it goes immediately to the Racors where it is clearly visible and drained whenever we see it.

[Off Trail]

With that level of gunk in the filter, I'd disassemble and clean the ball valve in the racor as well, once the filter is running clean.

[GordMay]

Originally Posted by boatpoker

Algae cannot form in diesel fuel tanks as it needs photosynthesis to survive and propagate. The Algae-X people created a snake oil business with this mythology. There are various bacteria than can form but not algae.

Somewhere over 24,000hrs. under power in my log now and have never added anything to my diesel fuel. Additives are already added at each refinery. Since I am not a chemist I would not try to out guess the refinery as to what other chemicals additives are advisable or even necessary.

Indeed.
Killing the “diesel bug” wouldn’t solve your problem. Dead microbes are just as fouling as live ones [tho’ they cannot reproduce more “bugs”].
In order to remove sludge [whatever it is] from contaminated fuel, you will have to employ the use of a fuel polishing [filtration] system.

See also an excellent article:
Addressing "Algae" in Diesel Fuel ➥ https://axi-international.com/addres...n-diesel-fuel/

[David Mathis]

A few years ago, while at cruise speed, one of my engines (Caterpillar 3126, 420 hp)stopped and would not start. The boat has the Raycor vacuum gauges so it was easy to see the problem, the starboard needle was well into the red and didn't come down when the engine quit. The fuel system was plugged. The other engine ran fine. Each engine has it's fuel tank. We were close to a marina so we headed to the service dock. The mechanic advised pumping both tanks and started with the port side which was crystal clear. He then pumped the starboard tank and found what looked like Hershey's syrup. It was completely opaque and had black chunks floating in it. It was so thick that it had plugged the intake pipe in the tank. After removing all the fuel then a few flushings of the tank, it was refilled, the filters changed, and we continues to our destination with no further issues. At the end of the season, the port filter was clean while the starboard Raycor was very dark although it still passed fuel with the vacuum needle in the white (barely). Now, a few years later, both filters are clean at the end of the season. The tanks were always filled at the same time, although occasionally different marinas were used during our trips, and both tanks received Bio-bore before winter storage. We found it odd that the fuel in one tank was clean but the fuel in the other was heavily contaminated.

[RedneckRedcoat]

You need to get the fuel polished. A day tank will not work unless you connect the return feed from your engine. Connecting a single hose to the engine will mean it uses the fuel fast and dumps what it doesn’t use in the main tank.

The issue you have is with condensation getting it it he tank. You should also use a funnel filter when filling the tank. Fill jerry cans first then then fill the main fuel tank with the jerry cans.
As others have said strip the racor down and clean that.