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Old 09-17-2023, 11:23 AM   #1
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Rocks in fuel tank

Having some trouble with the diesel aux in the sailboat getting starved for fuel. I opened the clean out and discovered a variety of what I can only call rocks in the tank. They are black, sharp edged, can be crushed or broken with some effort into a gritty black substance. I vacuumed them all out with a polishing rig I built, though I think there may be some still stuck in the hoses and fittings on the way to the filter. The are big enough to clog a 1/4 ID draw tube, and on a couple of occasions I had to back them out of the 1/2 ID suck tube on the polishing rig. Most of them in the 1/8 - 1/4 rough diameter, some as large as 3/8.

Asphaltenes? But most of the descriptions of asphaltenes are more like black sludge. This is rocks. Rolling around on the bottom. Their density is more than diesel, but not so high that you can't stir them up a little off the bottom before they settle again, which allows them to get sucked up in the dip tube. Anybody seen anything like that?
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Old 09-17-2023, 01:23 PM   #2
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Greetings,
Mr. DDW. Just a WAG here but perhaps the "rocks" are the next stage after sludge.
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Old 09-17-2023, 03:05 PM   #3
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Greetings,
Mr. DDW. Just a WAG here but perhaps the "rocks" are the next stage after sludge.
Probably. As to the pickup tube being blocked, maybe remove the engine end and blow air through it.
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Old 09-17-2023, 04:10 PM   #4
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I had something similar on my port tank but they were brown. Like sediment. I cut a hole in the tank and used a Seabuilt access panel to close. The only way to remove is to mechanically clean them. I would think backflowing from the Racor or filter line back to the tank with some compressed air would be sufficient to call it good.

Then of course change racor..run a bit..and change racor again.
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Old 09-17-2023, 06:36 PM   #5
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I ran into the same problem but mine were smaller than you describe. Fuel flow from my port tank was greatly restricted. I went nuts trying to find the blockage. I had removed the pickup tube expecting to see a blocked screen at the bottom. No screen. Finally I realized I could unscrew the tube from the elbow at the top. There was the screen! Full of little black sharp edged rocks. I pulled that screen out and threw it as far as I could. Did the same for starboard tank which oddly didnít have rocks. Iíd rather the rocks went through to the Racor where they were easy to deal with.
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Old 09-17-2023, 07:42 PM   #6
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It would be great if they would go through to the filter and get trapped there. I've spent two days on this so far, fortunately the tanks on the sailboat have pretty good access and can even be removed from the boat if needed. The aft one has not been used in several years and left dry. It had black deposits a little like sludge, very thin like paint, just a splattering. For forward tank which is used most had the rocks. Sailing on the Bay, I use very little fuel, just getting into and out of the berth so this fuel was purchased in 2018 (and still plenty left).

There is a suction dip tube in each tank leading to a 90 deg fitting, hose, selector valve, hose to the dual Racor. No rocks in the Racor. I tried blowing back through from the Racor, seemed clear. After cleaning the aft tank, I pumped all the fuel into it from the forward, and then ran the engine successfully, showing <3 in vacuum. Then I blew back through the forward tank again, switched back to the aft, primed with the priming pump and got 7" vacuum. I know it will not run with 7" vacuum. Blew back through the aft tank, primed, seemed to be Ok for a second and then back to 7". So I think some rocks got past the selector valve and are floating in the hose from there to the Racor. When there is flow, they get as far as one of the fittings and jam. Switch to the forward tank and get 7" even though there is no fuel in it. That hose is the only common element until after the Racors, and I don't think anything gets past them.

Next days attempt will be to remove that hose (Push Lok so have to cut it) and suck with a suction pump to see if I can get any rocks out.
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Old 09-17-2023, 07:46 PM   #7
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At this point I think I would pull the hose off the fuel tank and blow back through the pickup. Then put new hose on.
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Old 09-18-2023, 06:42 AM   #8
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I once had some solids in my tank. I would describe them as ď large coffee groundsĒ. They clogged my fuel lines 2 times and shut me down. Once I found a piece blocking the fuel line at a brass T, it was stuck in the fitting at the male flare.
Second time it got stuck in a brass fitting going into the Racor and by cycling the shutoff valve it broke it apart and I was off and running again.
Found the root cause to be a broken filter at the fuel dock. A fellow marina boater also discovered the same problem but several weeks after my discoveries.
After the second incident I started draining the fuel bowl after ever trip. I got a few more smaller particles but never got clogged again.
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Old 09-18-2023, 06:54 AM   #9
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We just replaced a fuel tank two months ago. The sludge in the bottom was sharp and crusty. I believe it was rust scale from the inside of the tank. I posted sludge pics on a thread I posted of the job.Click image for larger version

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Old 09-18-2023, 10:21 AM   #10
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No rust scale in these not very old aluminum tanks.

I'd be a little more believing if there was a layer of asphalt sediment hardening into rock, then breaking off. That is not the case in this tank, no later of sediment, no layer of sludge - just discrete rocks. Still a mystery to me.

I think one or more has gotten by the first fittings and is stuck between some others. Since the barbs have a smaller ID than the hose, they are getting trapped going either way - can't suck them through, can't blow them back. Probably this is a good argument not to use the Push Lok hose as you cannot remove to flush them it without cutting it off. I can replace the hoses, access to do that is a bit more difficult and at $7/ft you have to cut them up if they are not the problem.
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Old 09-18-2023, 05:59 PM   #11
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Next days attempt will be to remove that hose (Push Lok so have to cut it) and suck with a suction pump to see if I can get any rocks out.
Any chance to disconnect both ends and then use some higher pressure...like a small compressor to shoot some air with some pressure and velocity? Shoot into a bucket with a rag.
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Old 09-18-2023, 06:34 PM   #12
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Only way to disconnect the hose is to cut it. I have disconnected the tube at the Racor selector valve, tried blowing back through with an air tank at 60 PSI but there wasn't enough volume flow to be convincing. I think I will try with a real compressor before I break out the utility knife. If something got sucked in there I must be able to blow it out?
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Old 09-18-2023, 07:14 PM   #13
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Only way to disconnect the hose is to cut it. I have disconnected the tube at the Racor selector valve, tried blowing back through with an air tank at 60 PSI but there wasn't enough volume flow to be convincing. I think I will try with a real compressor before I break out the utility knife. If something got sucked in there I must be able to blow it out?
60 psi is quite bit. Obviously 100-120 would be better.

You would think if it went in under vacuum it should go out under pressure. But who knows. It seems likely its related to the rocks...but it could still be a "flapper" or some other kind of hose issue.

Well..at least you have it narrowed down. It will get fixed one way or another...lol. Hopefully its the easy way.
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Old 09-18-2023, 11:52 PM   #14
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The air tank was 60 psi on the gage, but I think there was a lot of pressure drop out of the tank to the fitting I was trying to blow through. The fuel hose is rated for 400 psi, so not much danger in blowing it up. I was blowing back into the fuel tank so if any rocks came out, I'd find them there.
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Old 09-20-2023, 01:05 PM   #15
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The rocks might be debris from welding process.
Iíve seen welded steel tanks put into service without without a good cleaning develop a veritable beach at the low end!
Some heavy equipment mechanics will insert round rocks to a fuel tank to stir up sludge on the bottom!
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Old 09-23-2023, 09:43 AM   #16
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These people ended up removing the tanks, cutting inspection holes for access to manual cleaning.

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Old 09-23-2023, 10:52 AM   #17
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Rocks aren't from welding. There was one small bit of aluminum welding flash.

I already have large cleaning ports, allowing me to reach every corner of the tanks.
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