How clean should a diesel tank be?

[boatpoker]

Originally Posted by SailingHarmonie

That of course has its advantages, but would not pass on a USCG inspected vessel, or on any new boat build.

I wouldn’t do it myself because of the risk of an uncontrolled spill. But it is your boat, and your risk assessment is different than mine. My tank is also set up so I can easily reach down to the deepest point with a hand pump to see what lives there.

A bottom feed tank is not prohibited on a pleasurecraft. Neither in CFR 33, 46, ABS nor ABYC standard that I can find.

Please cite such USCG ruling against bottom feed.

[Ken Goodings]

After each sailing season we planned to have minimum fuel left in our 30litre tank, perhaps only 10 litres or less.
Using our manually operated oil change pump we'd suck out as much of the remaining fuel via the 6 inch inspection port that we installed previously.
https://search.app.goo.gl/XUcCMZ6
The fuel was donated to commercial fisheriesy vessels.
Then my wife's long arm, a wooden ruler with wads of paper towelling and a bright light enabled thorough cleaning of the grit, algae and other junk from the nearly dry tank bottom.
Refill with clean fuel via a Baja type filter funnel.
Also, we recommend temporally removing the fuel dip tube to eliminate the intake screen at the bottom end. If it clogs at sea with a filled tank it's impossible to clear of debris.
We run a 10 micron Racor 500 fuel filter, then a 2 micron filter in series, and a 2 micron spin on filter on our V- P diesel engine.
After 18 years cruising from Toronto to Caribbean, never experienced any filter clogs at all.

[SailingHarmonie]

Originally Posted by boatpoker

A bottom feed tank is not prohibited on a pleasurecraft. Neither in CFR 33, 46, ABS nor ABYC standard that I can find.

Sorry, 33 CFR § 183.518 applies to gasoline tanks only....

[Colin Stone]

This clean. Mrs S with vacuum cleaner in tank.

[MJH]

Originally Posted by efanost

I tried to clean the 90 liter diesel tank from the inspection hatch on my Najad 331. I did it with a manual squeeze pump, trying to suck the dirt I could see at the bottom. On the pictures, you'll see the bottom of the tank after cleaning and the plastic bottle with the dirty diesel that came out.

I've never opened a diesel tank before and I wanted to ask you:

- Do you think what came out is a lot, a little, or just about normal for a 23 years old boat? (I don't know if the tank has ever been cleaned, for sure not in the last 8 years)
- Is the residual dirt on the bottom acceptable or should it be removed completely to avoid potential blockages or other issues? The dirt that came out is slimy in consistency.

You have a dirty fuel tank. If you sail in turbulent waters, which will put tank dirt into motion, they need to be emptied, cleaned, and fuel filtered.

I had my fuel tanks professionally cleaned by the same company that services the backup generators for Microsoft a year before my roundtrip to Hawaii.

Their truck came to the marina and emptied the approximately full 2x75 gallon tanks to their truck.

They then removed the servicing caps and wiped the inside of the tanks of all dirt/grime...they had to use a pickup stick to retrieve a small foreign object in the bottom of the starboard tank. This might have been the first time the tanks had ever been cleaned.

Once cleaned, they filtered the fuel while refilling the tanks adding a biocide and stopping occasionally to change filters a few times when indicated by their equipment. I also requested them to measure the total capacity of each tank during the filling to insure I knew exactly what they were...75 gallons each.

Lastly, they replaced the caps with new gaskets. Total cost was $1415 in 2015.

Due to insurance snafus and numerous boat items, I couldn't go until the following year. So, we cruised British Columbia instead.

In Hawaii, about 14.5 months after the tank cleaning, I drained the Racor and changed the 2 micron filter...it was dirty after only 266.9 engine hours and 77.4 hours after the last Racor filter change.

So, if you propose sailing/motoring offshore or in turbulent waters take extra precautions with your fuel system.

[Foswick]

I think this has been answered across a number of posts, so I don't have much to add except to may paraphrase.

That tank is not unusually dirty for a tank of that age. If you sample 100 random tanks of similar vintage, you're likely to see 20 or so that are worse. (That is a number completely pulled out of thin air - not at all based in reality.)

And, tanks far dirtier than yours operate for years with no issues. They are problems waiting to happen, but the reason tanks get that bad is because they do not cause a problem until they do.

As has been pointed out, if that gunk gets dislodged, it can foul a number of things downwind. Fuel filters will help prevent some of the worst of them, but in reality, a failure is most prone to happen when you need the engine the most (in rough seas), and when you are least able to do something to fix the issue.

I do appreciate the question. It raises a great discussion that impacts anyone with an inboard fuel tank and it is something that doesn't receive a lot of attention. There are a lot of topics that people go overboard with overcautious advice, but I think the consensus is spot-on here - there is no such thing as too clean. For me, the only thing more important than having a boat that floats is having a reliable engine.

(Ironically, my current boat does not reflect these values ... yet, but that's another story. I'm working on it.)

[Dockhead]

Originally Posted by Foswick

. . . As has been pointed out, if that gunk gets dislodged, it can foul a number of things downwind. Fuel filters will help prevent some of the worst of them, but in reality, a failure is most prone to happen when you need the engine the most (in rough seas), and when you are least able to do something to fix the issue.. .

That's the crux of the matter, and the reason why clean tanks are essential!

A fuel problem from a dirty tank might not give you the slightest problem until that one day when it's very rough and having engine power may be a matter of life and death. There are countless stories like this.

You can't just carry on waiting for the problem to show itself on some pleasant day in good weather so you can fix it at leisure. That's not when the problem will occur.

[jadams4037]

This is the most important thing in operating your boat. Forget polishing on your own. There are companies that will drive to you or boat to you. Construction companies, highway builders, and buildings with large generators always polish their fuel. Reach out to them for information to have that peace of mind..All it takes is one speck of anything to ruin your enjoyment of your boat OR - pull the tank out and visibly clean or replace. Ask your fellow sailor friends who have a lot of experience.

[KWISPEL]

Not abnormal for a stainless steel tank of this age. Just drain it, put old diesel in the (trash) and clean tank with a rag.
Install new diesel filters and when filling, check for debris coming out of the hose when filling.
Mix a Biocide into the diesel such as Grotamar 71 and keep using it!
Only tank diesel where you are sure it comes from clean tanks.

[Ballsnall]

Originally Posted by Foswick

That tank is not unusually dirty for a tank of that age.

Exactly, if that is the first time that tank has been cleaned then it is in remarkably good condition. Diesel tanks are notoriously dirty but generally do not cause issues, that is due to dirty fuel which is a completely different issue.

And, tanks far dirtier than yours operate for years with no issues.

Regardless of all the advice to polish your fuel, this will do nothing for a dirty tank. The best advice is to just drain off the water and sludge regularly so the fuel doesn't get contaminated. Other than that, your filters will handle the occasional stuff that gets dislodged but most of it will just settle to the bottom of the tank.

[OneBoatman]

Yes to fuel polishing if available to see if it could impact getting the rest of what you see in your tank. Judging by your pictures my opinion is you did one heck of a job manually. Clearly some debris or growth still present but I think you will be fine providing you begin using biocide regularly and have replaced the primary in your fuel/water separator and put a new secondary filter on the engine, as new I think these are typically rated about 7-12 microns. If you use a 10 in Racor it may need more frequent replacement than using a 30 micron in the Racor. Remember filters become more efficient as they do their job at the expense of back pressure, so we use back pressure as indicator of age. After 50 hours I suggest you remove the primary cartridge from the fuel/water separator and take a look at the media. If you see significant debris on the media that will tell you how you're doing. Then re-examine the tank, it certainly shouldn't look worse than that original after pic. People with older boats having original fuel tanks are more likely to starve their engine by putting in too fine a filter such as 2 micron filter. Debris that you can actually see will easily be removed by your filters. No particulate under 10 microns will threaten your injectors.

[bgallinger]

Originally Posted by SailingHarmonie

A diesel tank should be spotless. NO water, NO gunk, NO suspended solids, NO foreign matter. That tank is filthy and your engine would likely stall in rough seas as that crap got mixed to the point it reached the intake line and clogged filters, or worse, injectors.

Seriously, your diesel tank should be cleaner than your potable water tank.

Have that tank professionally polished before you run the motor.

SailingHarmonie nailed it. Nothing in the tank but diesel fuel!