DeFever 48 - Trying to understand how my fuel system works

[f508]

Hi,

I think I have an intermittent fuel blockage. After the boat rolls I sometime experience a partial or complete power loss on the starboard side. I've inspected and replaced my primary filters and my Racor filter and they were clean. So I currently think it is debris at the tank pick up.

But it looks like my fuel from both sides seems to join and be distributed through a common manifold. Can you guys tell me it that is right?

I ask because if that is the case then the blockage has to be between the manifold and the engine and not in in the tank, because it could simply draw from the opposite side through the manifold, and the engine wouldn'd fuel starve.

Thanks in advance!

Frank

 

[High Wire]

Thats what I see.

 

[Wxx3]

The first thing I would do, is to feed and return to only one tank to help you isolate the problem.

 

[sunchaser]

The first thing I would do, is to feed and return to only one tank to help you isolate the problem.

Yes.

Note I have a DF 48. Since day one that has been my tank management method. Also, when did this issue begin? Just after some maintenance maybe?

 

[Lepke]

Rolling tied to fuel loss is usually either low fuel or debris moved by the rolling blocking the pickup tube or debris moving somewhere else and blocking the fuel system. Do you use a biocide as part of a conditioner in your fuel? The tank like manifolds seem a great place for organism growth if a conditioner isn't used regularly. They letting debris settle out of the fuel and both engine supply lines are at the bottom. Is there a drain at the bottom? For starters, I'd move both the engine supply lines to the manifold top.
How much fuel do the engines pump and return. If the flow is low, another reason organisms might grow in the manifolds and any water would collect in the bottom with no way out unless there's a drain.

 

[f508]

Hi Lepke,

I use Biobor as directed at fill ups.

No there isn't a drain on the bottom of the manifold. But since the aft fuel tanks are decommissioned I have unused fittings on the manifold. So I can do as you suggest and move the engines to the top and shift the decommissioned spots to the bottom, and fitting a drain to the bottom.

Good idea!

 

[f508]

Prior to October 2nd all engines run normally. I put over 400 hours on the engines in the last year, and I use Biobor as directed at fill ups.

On October 2nd fuel level was at about 100 gallons per side. I add an additional 100 gallons per side, starting with the starboard tank.

The 1 hour run on October 2nd from the fuel dock to my berth is in smooth conditions and everything runs normally.

Starting around October 4th, through October 7th I notice an occasional subtle and momentary roughness (duration about 1 second, and frequency of about once an hour.) This period coincides with some fairly windy weather and rough seas so I wasn’t sure if it was the sea or an engine issue.

On the afternoon of October 7th heading home with some consistent beam seas, my starboard engine becomes rough for about 60 seconds, and then dies. I continue on the port engine until I get to a sheltered area with no traffic and go below and look at the racors. They look OK. There is less that ½ inch of water in the bottom of both of them. I drain them both and try to start the starboard engine. It starts but will only run at idle and only for a couple of minutes at a time.

After I get back to the dock I change the racor filter and the 2 primary filters on the starboard engine. They all look very clean (I disassembled the primaries so that I could see the filter material.)
Although I never found any debris, the engine ran normally once again in calm conditions for 3 hours. At that point, taking a wake on the beam the boat rocked and I got about 30 seconds of roughness followed by engine failure. At this point I am thinking that there is debris in the starboard tank that can slosh up from the bottom high enough to obstruct the fuel tank pick up.

It happens that a previous owner had plumbed an electric fuel pump off the port tank for priming, so I shut all the valves except the ones for the starboard tank and the priming pump and back fed fuel from the port tank into the starboard tank thinking that it might clear the debris from the pickup. After this, and returning to what has been my normal configuration of both fuel tanks on, and feeding the manifold, the starboard engine started but would not run smoothly above 1500 rpm, and would die immediately above 2000 rpm.

I was thinking I had the debris in the tank, upon reflection that doesn’t make sense because the port tank was also available to feed that manifold, so even with the starboard tank blocked there should not have been an interruption of the fuel flow.

So now I am thinking the debris has to be in the fuel line between the manifold and the racor on the way to the engine.

 

[f508]

Hi Sunchaser,

I have never thought about using 1 tank at a time. I assumed I wanted to keep the tanks even, so I ran them both at once.

Is it customary to use an alternating fuel burn system as opposed to both at once?

 

[sunchaser]

Hi Lepke,

I use Biobor as directed at fill ups.

No there isn't a drain on the bottom of the manifold. But since the aft fuel tanks are decommissioned I have unused fittings on the manifold. So I can do as you suggest and move the engines to the top and shift the decommissioned spots to the bottom, and fitting a drain to the bottom.

Good idea!

Think twice about moving engines to the top manifold

Takeoff location is likely not the problem and moving to top manifold will likely cause more. The engine take offs at the very bottom manifold location provide gravity feed to the first stage of filters even with partially filled main tanks. The top manifold is all your returns as well. You can easily gravity drain the individual bottom take offs to insure they are flowing.

 

[f508]

I'll check. but I am pretty sure that even at a higher location, I will still have gravity feed from the tanks to the racor, and it is uphill from there either way.

 

[sunchaser]

F508
When you disconnect engine fuel lines at manifold check for flow and screen for debris into a good sized bucket. If flow good and no debris look elsewhere.

How old is lift pump - any leaking fuel lines after the manifold? Try switching port to starboard engine takeoff at the manifold and see if problem moves to other engine.

 

[f508]

The lift pump is old, possibly original, but it is working.

There aren't any leaks.

I am in the process of figuring out the thread sizes to replace most of the fuel lines. They are mostly copper now and are anchored down so securely that it is hard to disengage the tubing from the compression fittings to check the flows. The first one will be from the manifold to the starboard Racor. Then I need to plumb a way to move the fuel in the starboard tank to the port side to clean the tank. Fortunately, the tank has a maintenance port installed.

My current theory is that debris from the starboard tank has partially clogged the line between the manifold and the racor.

So the plan is:

1. Remove the line from the manifold to the starboard Racor.
2. Flush and inspect the manifold.
3. Replace the line from the manifold to the Racor
4. Plumb in a method of transferring fuel between tanks.
5. Transfer most of the fuel to the port tank.
6. Open and clean the starboard tank.
7. Transfer the fuel to the now clean starboard side.
8. Clean the port tank.
9. Equalize the fuel.

 

[kchace]

I think your plan is sound. If you find ANY liquid water in your Racors then you probably have quite a bit of water in the tank(s) and most likely a lot of debris from biological action.


Ken