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osprey877 · 15-12-2021, 18:39

Quote:

Originally Posted by MicHughV

Some years ago I swapped engines on my boat. As part of this endeavor, I also removed the original diesel tank, as I planned to replace that as well.

Once the old tank was out, on a whim, I took the access cover off to take a peek inside.
That tank was maybe 7-8 years old.

Lordy, lordy, lordy...I did not expect to see what I saw. The bottom and lower sides, about 3-4" up the sides, was covered in black gooey slime, about 1/4" thick. I have since researched the cause of this, but regardless, this is quite a common problem for a diesel fuel tank.

I don't see how the inside of a tank can be cleaned thru' the fuel pickup hole alone, as access is severely limited.

The tank (like mine) may also have baffles inside to prevent fuel from slopping around, which is another reason why the fuel pickup hole will not work.

I think all the fuel needs to be removed to clean this goop out of the tank, as you don't want it mixing with any residue fuel.

My fuel pick up line extended down to about 1 1/2" from the bottom of the tank, pretty darn close to this goop.

There's pretty much no way around this. You need decent access to all corners of the tank.

I have no idea how one would go about cleaning this. Pressure washing maybe ?? A long bristle brush ??....various solvents...yards of paper towels....heavy rubber gloves..it would likely be quite a project.

It would be a long arduous, filthy, dirty project, no doubt, but once done, you'll be happy you did it.

I do know that there are companies around that specialize in this type of cleaning, an internet search will likely turn up something.

From my point of view, I'd get a pro to do it, no two ways about it.

You note that the sludge was thick and gooey. If so, then it would have been detectable with a sharp stick or rod inserted through the sensor hole and dragged along the bottom of the tank. I tested my 30 year old fibreglass tank this way and the stick came up clean. Prior to the test, I had phoned a commercial marine fuel tank cleaning firm to get an idea of the cost, and when I told them I had a fibreglass tank, the operator said he'd be surprised if there was much sludge at all in the tank and that it was usually steel or aluminum tanks that had a problem.

After my stick drag test came up clean, I decided not to bother with the tank cleaning. Mind you I am in the PNW where there is no fuel cleanliness issue and the tank doesn't get too hot like down south. I also keep the tank full and I don't have any problems with premature fouling of filters etc.

The OP may want to test the cleanliness of the tank with the sharp stick test through the sensor hole before going to the expense of commercially cleaning the tank, as it sounds like he doesn't have a problem with clogging filters etc. Unless of course there is a hard sludge problem I don't know about that might not be detected with a stick through the sensor hole??

MicHughV · 15-12-2021, 18:54

and they tell me boating is supposed to be fun...

MicHughV · 15-12-2021, 19:05

Well, I never thought to check the cleanliness of my diesel fuel tank. My discovery of the sludge/slime was only occasioned by my curiosity when the tank was removed, but I have since learned that this is not an infrequent problem.

Some tanks are difficult to access, compounding any possible inspection procedure.

Dirty fuel (or water) is typically first noted at the fuel filter if this monitored on a frequent basis ( as it should be)

As always, it's each to his own to do what they think they need to do. Just relating my experiences and point of view.