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Old 10-13-2019, 07:31 PM   #1
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Not drawing fuel issue.

I topped off the tanks 3 weeks ago and we have been making some good weekend trips, about 8 to 10 hour round trips. I started off with appx 300 gallons, 150 in each tank. Today i noticed a slight list to starboard. Still 150 in that side and only 50 in the port. The tanks are joined at the bottom of each tank with a connecting line. There is a stainless steel small tank with two input lines coming from the top of each fuel tank directly over the big racor filters. There are three valves on this tank. One valve to the port racor and one for the starboard, and a center valve I am assuming goes to the Onan. I checked all the valves and they are all in the same open position? The output valves at the top of each tank are also both in the open position. Clogged line from the top of the tank feeding the racor? Maybe? Anyone have any thoughts? My first trawler, my first twin engine diesels, am learning as I go along. There are no electric valve switches to turn the tanks off.
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Old 10-13-2019, 08:02 PM   #2
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PPhil,
Is it possible that your fuel return goes to the fuller tank?
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Old 10-13-2019, 08:03 PM   #3
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You need to determine a couple things. First figure out where the feed lines are for each engine. It sounds like you may have done that. The next is to determine where the fuel return goes from each engine. Finally, check to see if there is a valve on your connecting line and whether it is open or closed.
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Old 10-13-2019, 08:17 PM   #4
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I had a similar problem that drove me crazy. It turned out that the screen on the fuel pickup tube on one tank was mostly blocked. The screen was hidden at the top of the tube where it screwed into a fitting. I pulled the screens from both tubes and threw them as far as I could. I want the dirt to get to the Racor where itís easy to get rid of.
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Old 10-13-2019, 08:32 PM   #5
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I had a similar problem that drove me crazy. It turned out that the screen on the fuel pickup tube on one tank was mostly blocked. The screen was hidden at the top of the tube where it screwed into a fitting. I pulled the screens from both tubes and threw them as far as I could. I want the dirt to get to the Racor where itís easy to get rid of.
+1 on the screens.
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Old 10-14-2019, 01:55 PM   #6
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Okay I checked to see that each engine(Volvo TAMD-41A) has a return line and they each go to the tank they are nearest, ie starboard to starboard tank ect. I traced the pick-ups to the stainless tank above the racors. I also noticed a lot of what appears to be black particles built up in both racor bowls. So Iím betting that I have a clog. I am going to try this and please give me your thoughts. I am going to replace the racor filters and the fuel filters on the motors, then take some compressed air and blow back into the line to the tank and see if there is an obstruction. Then if I hear bubbles in the tank I should be able to draw fuel back to the racor assembly. Maybe. Thanks for all you advice. Itís all been super helpful.
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Old 10-14-2019, 02:25 PM   #7
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I had a similar problem with fuel starvation when using Gulfcoast fuel filtration Walbro pump. The pump would tick tick tick then move fuel slowly to the Gulfcoast filter. I removed the pick up screen and the pump worked as it should without the restriction.
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Old 10-14-2019, 02:44 PM   #8
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You most certainly will be able to blow the blockage from the screen on the intake line. In fact a common problem is an engine chocking off from lack of fuel. Waiting a half hour or less after shut down often corrects the problem, BUT ONLY until the crud gets sucked back onto the screen. See HopCar note. You need to get rid of the screens, let the Raycors catch the crud.

If you have bottom drains (doubtful) you can probably drain a lot of the crud that way. (Marine construction codes do not allow bottom drains)

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Old 10-14-2019, 03:56 PM   #9
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Actually there is a line that connects both tanks it is located at the bottom of rack tank and there is a small valve at each end. So draining the tanks would be easy once I ran the fuel below say 20 gallons in each. The tanks sound like the old black iron tanks when I tap on them however they have been coated with a fiberglass type resin. The engine bay though 30 years old looks like it was extremely well maintained. The previous owners say that the fuel draws evenly. So Iím hoping itís just blockage.
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Old 10-14-2019, 04:09 PM   #10
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First I would replace all fuel filters and clean the Racor bowls. Second, I would set the starboard engine to draw and return to the starboard tank, port to draw and return to the port tank. Now go for a run and see if you stall out one of the engines. I believe it’s more likely you have miss understood the valves on the boat than a clog. However, neither can be ruled out just yet.
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Old 10-14-2019, 04:56 PM   #11
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Just something to think about. If you have a bunch of crud in the bottom of old steel tanks and then you get the crud removed, the tanks may leak. Sometimes the crud is plugging the pin holes in the tank. So be careful how aggressive you get in cleaning the tanks. Do you have access panels in the sides of the tanks? Donít remember if you said you did or didnít have access into the tank. I am getting ready to haul my boat this week and then pull the port engine so I can replace the port fuel tank just in case... My tanks are steel and 32 years old so I think they have run their course. I am going to replace them proactively. Good luck with yours.
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Old 10-14-2019, 05:02 PM   #12
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Originally Posted by tiltrider1 View Post
First I would replace all fuel filters and clean the Racor bowls. Second, I would set the starboard engine to draw and return to the starboard tank, port to draw and return to the port tank. Now go for a run and see if you stall out one of the engines. I believe itís more likely you have miss understood the valves on the boat than a clog. However, neither can be ruled out just yet.

This makes the most sense to me. Changing the Racors and cleaning the bowls is a pretty easy job should be done.



Since the fuel returns to the tank nearest the engine, I would look closely to see if their has been fuel leaking out of the fuel vent on the side that the tank stays full.
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Old 10-14-2019, 05:07 PM   #13
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I helped the owner of my old boat out with a situation where some tanks seemes to drain faster than others. Some of the supply valves were clogged with crud, but the valves themselves worked fine.

If you have a crossover between tanks, it could be a similar issue. I cleared the clogs from the outside using a small bucket and a plastic wire tie.

Sadly a week later a tank leaked on him. They were old steel tanks, but surprised me. I wouldn't bet on crud plugging leaks -- but, heck, maybe.

He's replacing them now.
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Old 10-14-2019, 05:17 PM   #14
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I helped the owner of my old boat out with a situation where some tanks seemes to drain faster than others. Some of the supply valves were clogged with crud, but the valves themselves worked fine.

If you have a crossover between tanks, it could be a similar issue. I cleared the clogs from the outside using a small bucket and a plastic wire tie.

Sadly a week later a tank leaked on him. They were old steel tanks, but surprised me. I wouldn't bet on crud plugging leaks -- but, heck, maybe.

He's replacing them now.
That is what I was getting at. If there is a lot of crud in the tanks when you clean them out, I would be prepared to replace them, if you can be prepared...
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Old 10-14-2019, 06:50 PM   #15
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We had one tank not emptying and it turned out to be a blocked air vent hose.

Suggest starting with the least complex possibilities first.
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Old 10-14-2019, 07:27 PM   #16
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(Marine construction codes do not allow bottom drains)

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There is no such restriction in either ABYC nor CFR's for diesel tanks although there is for gasoline tanks.
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Old 10-14-2019, 09:06 PM   #17
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Murray is right. The first place to look is the tank vent. It’s not uncommon for Mud Dauber Wasp to block them.
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Old 10-14-2019, 11:44 PM   #18
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Murray is right. The first place to look is the tank vent. Itís not uncommon for Mud Dauber Wasp to block them.

If the vent is blocked, what happens since one engine returns fuel to that tank?
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Old 10-15-2019, 10:00 AM   #19
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If the vent is blocked, what happens since one engine returns fuel to that tank?
Good question, I donít know, but I was on a boat once that had itís diesel engine shut down by a wasp nest.
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Old 10-16-2019, 07:09 AM   #20
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"You need to get rid of the screens, let the Raycors catch the crud."

The problem with removing the screen is any large chunk can block the fuel pipe.

A much longer screen ,say 6 inches of screen tube , will still pass the desired fuel with out just a single chunk blocking the pickup.
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