Replace the diesel or not??

[Annabel]

I hope this is in the right forum. We are returning to our yacht in Greece after the extended time of 2.5 years because of Covid (Grrrrr) we are a bit worried that our diesel may have developed a bug problem. My husband is rather convinced that we should empty the tank and replace it with new diesel. Any views on this anyone? Thank you

[dlj]

That's not an easy one. How many gallons are you talking about? How old is the boat? What is your normal diesel pattern with usage and filling?

Generally, I would not be overly worried, I'd make sure I had a couple extra fuel filters.

It does depend on what you are going to do with the boat when you get back to it. Are you going to coastal cruise a bit or are you taking off for a long haul? If the former, I'd be less concerned. If the later, I would agree with your husband. Did you put any kind of stabilizer or biocides in the tank before leaving it? To many unknowns here to give much more that that.

dj

[sailorboy1]

Replacing the diesel probably wouldnt as the “bugs” are on the walls and bottom of the tank

Look up “fuel polishing” instead

[Sand crab]

Yup, Fuel polishers have portable rigs that will siphon the fuel out of your tank at the dock and clean it and put it back in. Or you can buy and install your own system but for a one time cleaning it's way cheaper and easier just to have them come out.
https://www.usafuelservice.com/work-gallery/

[tkeithlu]

Good advice above.

Let's see if we can organize the answers.

First, how bad? If it's a little sludge, filters will take care of it. If it's jello, then it's either throw it out or have it polished.

Second, how much is it? A small amount can be filtered, but is not worth having a contractor come polish it. It can be tossed. A large amount will be expensive and difficult to toss, may exceed the capacity of your filters, and may be worth polishing.

[bil56]

Have you added an effective biocide to your diesel?
at start-up, it is possible to add a curative and non-preventive percentage ...

./.

[Flatswing]

Typically “ bugs” grow at the water/diesel interface, so if u have never had an issue with water/bugs in fuel previously, you are probably fine. Take extra primary (Racor or equivalent) filters in case. I have missed a season or 2 of use with old fuel - if no water, still good as new.
If you have had to drain water in from primary filters previously, then all bets are off unless you routinely add an algicide. As others have suggested, if small amount of fuel left in tanks, discard it. If large amount, you will either go through a case of filters or require professional fuel polishing.
BUT: if you have a previous history of “bugs”/water in fuel, then know that the forums are rife with tales of boaters who had their fuel polished but still got into trouble in rough seas because the only way to properly clean tanks after major infection is to drain, and physically (manually) clean the tank surfaces - this usually means an inspection/access port to get all the adherent crud.
Bottom Line: if you never had a problem before then you ok with extra filters. If you are worried because of prior history-make robust cleaning plans.

[Arrandir]

I were in a similar situation, but left the boat half the time. Maybe this will help you decide.
I left the boat for 15 months.
The 150 L tank was full.
I plugged airhose to the tank and added biocide.
I pumped up diesel and found 0,4 L bugs in the bottom when I got back.
After one week I pumped up again, not much dirt came from the bottom this time.
I have now used the boat a few months, the engine have been running for 20 hours. No signs of water or bugs in the water separator.

[sail sfbay]

If the tank was not topped off to prevent condensation and treated with an enzyme diesel stabilizer to disperse water and mitigate algae sludge build-up then you might consider polishing the fuel, if that service is available. If you pump it out, you need to consider where to dispose of it. I returned from a 3-year overseas trip without a full tank and untreated diesel and my 40 hp diesel Yanmar operated fine. My guess is yours will run fine. But have spare fuel filters on hand and inspect them often.

[billgewater]

If the tanks were not full to the top then the thermal expansion and contraction of the air above can expose the fuel to water vapour. The water is the main villain in the deterioration of the fuel. Full sealed tanks can keep fuel good for years. Biocides do work as outlined above. There are "shock" level treatments and periodic treatments. Also, some engines are more susceptible to older fuel (I'm told by some mechanics).
Maybe you can have the fuel tested. There are usually testing possibilities from major fuel supply companies. They will advise if the fuel is salvageable and how to best do it for your fuel samples. Provide samples from the top and bottom of the tank(s).

[Nyaminyami]

If it's any help: the boat I bought had sat for 8 years with about 300 litres of diesel in a 1300 litre stainless steel tank. It was horribly contaminated with 'bacteria' - smelly, gloopy brown muck that was at the bottom of the tank like a giant amoeba and stuck in the angles of the tank and in the lines and filters.(If you have ever changed a nappy you would know what I mean:). But being a skinflint and loath to throw away 300 litres of precious fuel and after throwing away the old filters and cleaning the lines with a gun pull-through I drained the tank, pumping it out through several filters then washed the tank with caustic soda, hot water and a detergent and pumped the fuel back into the tank, again through filters. In all I recovered about 3 kilograms of gunk but the fuel that went back into the tank was bright, clear as honey or amber.
I used this fuel to motor across the Balearic Sea.

Post script: on the journey over I broke down seven times. The engine enjoyed the fuel but resented the small amounts of gunk that I had missed that accumulated in the filters until the fuel couldn't get through and one or other of the engines petered out. On each occasion I changed the filters and continued on my way. (The gunk I missed must have been in the top corners of the tank which only came loose during the rock-and-roll of the journey.)

Bottom line: once the fuel is filtered and cleaned you are good to go -provided the tank you put it in is just as pristine.

[Paul Howard]

I bought a boat in Florida that had been setting ashore for about 2years.
I suspected the fuel would be contaminated, so sent the suction hose from one of those hand pump vacuum engine oil extractors down the fuel feed opening and it reached the bottom of the tank to suck out a sample of the fuel from the bottom of the tank.
There was water and 'slimy gunk' there, so sucked out all the fuel and put in new.
The engine ran Ok until we got into some rough seas, motoring out a harbour entrance against the wind with a steep chop.
Fuel filters clogged and engine stopped, I was able to get the jib up and sail back to a place to anchor while I sorted things out.
I went ashore to get more gerry cans (luckily the tank was relatively small at 20US gallons.
The tank was under a locker and not too much cutting was required to remove the tank, as there was no inspection/clean out port. Once out, I could shine a flashlight into the tank fill opening and see green slime on the sides of the tank.
I was told gasoline kills diesel fuel bugs, so put in some gas as well as some clean crushed limestone rock from a driveway, rolled and rattled the tank around and rinsed with gas several times and got some really horrid looking gunk out of the tank.
Shining a flashlight into the tank I could see there was very little residue left in the tank, so re-installed and filled with fresh fuel. I regularly treat the tank with biocide.
There has been no further problems in the intervening 5 years despite several encounters with rough seas.

[Annabel]

Gosh this is amazing, thank you for so much information for us to consider. It will take some time to digest it all, but we are very very grateful to you all

[MJH]

Originally Posted by Annabel

I hope this is in the right forum. We are returning to our yacht in Greece after the extended time of 2.5 years because of Covid (Grrrrr) we are a bit worried that our diesel may have developed a bug problem. My husband is rather convinced that we should empty the tank and replace it with new diesel. Any views on this anyone? Thank you

Replacing the diesel will not solve the "bug" problem, as you call it; the walls of the tanks could be covered with the stuff. Much depends on how diligent you, and previous owners if applicable, have been in caring for the fuel and tanks.

Saildata.com says the Hans 455 was built between 2014 and 2017, so that would be 5-8 years of use, but it only tanks one use hiccup to get it started.

The minimal thing I would do would be to change the fuel filters upon returning to the boat and its first use. I would regularly check the primary filter, particularly if rough water is encountered which will stir up the fuel, and see if it was collecting more debris than normal. If not you may be OK for the season.

Another approach would be to have the tanks cleaned prior to any long offshore voyage. This entails pumping out all the fuel to a temporary tank, opening up the tanks and cleaning them thoroughly, then returning the fuel to the tanks after it has been cleaned. This process is a special service and not available everywhere and will take half a day or more. I had this done prior to my roundtrip voyage to Hawaii and it cost me about $1500 seven years ago.

Just having the fuel cleaned only gets it cleaned for the moment but the tanks per se remain dirty and the growth resumes. This was done to my new-to-me boat in Florida, paid by the seller, and I still had fuel problems. I had it done again a month or so later with better results. A lot depends on who is doing the job.

Good Luck.

~ ~ _/) ~ ~ MJH

[Bent Bugle]

Can you pump out some diesel from the tank, preferably from the bottom or the sides & see if the fuel is affected?. When I replaced my leaking s/s tank & peeked inside the sides were covered in patches of brown gunk. If you end up replacing the fuel you may want to use a biocide shock treatment as well, the bugs can also infest the lines...