Does your fuel tank have a strainer in it?

[Captain Graham]

I have a 27th sailboat with a 18 HP diesel.
When I increase the rpms the engine would start to die.
Lowering the rpms it would go back to running well.
So at high rpm the engine was not getting enough fuel.
I checked the 2 filters the external racor and the one on the engine they where just a little dirty so I changed them.
Still had the problem so I thought maybe the tank had a big chunk to something blocking the fuel outlet pipe at high rpms.
Emptied and cleaned the fuel tank did not find anything so I looked at the fuel outlet pipe.
To my surprise I found a small strainer inside the outlet pipe that was clogged.
I had no idea some tank manufactures put strainers inside the outlet pipe.

So I removed it and added a clear filter before the racor filter where I can see it.
The filters are
1. Clear filter 60 mil (to catch the big stuff)
2. racor 10 mil filter (to catch everything including water)
3. filter on the engine 25 mil. (really does not do anything but that is what the manufacture uses)

You may want to check to see if you have one and clean it before you have a problem.

[wrwakefield]

Good catch and root cause analysis. [And thankfully rather unusual from my experience in the boats I’ve had.]

One that got me on a different boat was the fuel with entrained air when the tank reached ~50%. I discovered a pinhole [corrosion] at that level on the pick-up tube in the diesel tank…

On yet another boat the symptoms you described were caused by the internal layer of good [but old…] Type-A fuel line collapsing- thereby greatly reducing fuel flow- under higher throttle [suction.]

All these causes are simple to describe, but take a lot of time and effort to discover.

Glad you found yours; Another contributing factor to add to the list…

Cheers, Bill

[Captain Graham]

Originally Posted by wrwakefield

Good catch and root cause analysis. [And thankfully rather unusual from my experience in the boats I’ve had.]

One that got me on a different boat was the fuel with entrained air when the tank reached ~50%. I discovered a pinhole [corrosion] at that level on the pick-up tube in the diesel tank…

On yet another boat the symptoms you described were caused by the internal layer of good [but old…] Type-A fuel line collapsing- thereby greatly reducing fuel flow- under higher throttle [suction.]

All these causes are simple to describe, but take a lot of time and effort to discover.

Glad you found yours; Another contributing factor to add to the list…

Cheers, Bill

You are so correct about now hard it is to find the cause of a problem.
And thank you for sharing your experiences with other causes to the problem.
I will keep them in mind if I ever have the same problem again

[FPNC]

This is more common than people think. USCG fuel tank requirements for inboard gasoline engines require a screen at the bottom of the pickup tube. This screen and also an anti siphon valve create a restriction and potential blockage point before the fuel filter. Not a good idea. Many installers do not remove the screen or anti siphon valve when a tank is used with a diesel engine.

These blockage points are not required by USCG for diesel installations.

[SailingHarmonie]

To screen or not to screen... It is not as easy a choice as you might think.

While a clogged screen inside the tank can be a troubleshooting challenge for people who do not know it is there, it should be a quick and easy check in a properly designed tank system where the dip tube can be quickly pulled and inspected. That should be a seasonal maintenance procedure. (Yes, I know that not all boat fuel systems are designed to allow this...)

But now imagine that an unscreened dip tube has sucked up a chunk of debris, and it has traveled down the fuel line, and lodged in an elbow or other constriction downstream where it staves the engine of fuel. THAT's a REAL nightmare to troubleshoot and clear up, especially if you have complex fuel piping. Somebody with this problem might just be cussing the boat builder for NOT putting a screen on the suction line.

Even diesel tanks kept clean and dry can, over years, accumulate asphaltenes that consolidate into a black, coke-like material that lines the bottom of the tank. This stuff is hard and brittle and can break into small pieces. I do not know of any way to remove this stuff other than actual mechanical cleaning. A properly screened dip tube (and certainly not all are done properly) can really save your day by keeping chunks from blocking or moving through the fuel piping. The thing is, if it works as it should, you will never know that it kept your engine running.

Poorly maintained diesel tanks that are wet and have bio-gunk growing in them will clog pretty much any screen, anywhere. The problem here is not the screen, it is what is in the tank. Fix that, and the screen will take care of itself afterward.

[thinwater]

A common problem with gas tanks is the anti-siphon valve, a small ball-check valve on the top of the tank (gas not diesel). The purpose should be obvious; it creates just enough back resistance to prevent siphon if a hose fails.


That said, a great many boaters get sick of it and remove it. I sure hope they maintain their hoses. On outboard-powered multihulls the only consequence is often a gas slick on the water, since the tank and hose train is in the bridge deck and drains overboard. On outboard powered powerboats the need varies with the system. Your portable tank in your tender has an anti-siphon valve, and they do occasionally block if you are careless with filler cap cleanliness.

[FPNC]

Originally Posted by thinwater

That said, a great many boaters get sick of it and remove it.

This is true. However, for gasoline fuel tanks, the anti siphon valve may be specifically required by law. Removing the anti siphon valve could open you to liabilities.

[thinwater]

Originally Posted by FPNC

This is true. However, for gasoline fuel tanks, the anti siphon valve may be specifically required by law. Removing the anti siphon valve could open you to liabilities.

Absolutely correct.

[pierluigi]

thx for all the info. I have a DV20 on my old Swan 371 in Miami. The engine was raving but running well up to 1000-1200, then stopped as if running out of fuel. Fuel is 5+ y old. I replace the fuel filters (engine and water separator) filled water separator with fresh fuel, engine runs perfectly. It will not pull fuel from the tank. Bad fuel pump? Do I need to prime the fuel line from tank to water separator filter?

[cory_reinking]

Just a word of caution from a really bad experience we had with our 27hp Westerbeke on a previous boat. Fuel tank was under the swim platform and the fuel shutoff ball valve on a pull cable didn’t close completely for fuel system maintenance. So we installed another valve right before the primary fuel filter for convenience. We weren’t in a place with lots of valves, and happened to find a suitable 3-way valve and capped off one end. Because I didn’t want a 90 degree bend at the valve, I inadvertently capped the input and used the two outputs. This was a huge mistake that resulted in similar symptoms where the engine ran fine at low RPM and seemed starved at higher RPM. No fuel would pass through the 3-way valve, which then blocked the fuel line. Eventually the fuel pump burned up and we realized we had a self induced blockage. But not before the engine was run for many, many hours drawing unfiltered fuel through the return line. The result was a 5 figure rebuild (15 years ago) due to scored cylinders and loss of compression in an engine that only had about 600 hours on it. Not sure if some other engine manufacturers implement a safeguard for this scenario or not, but just wanted to make sure everyone is aware of what kind of engine damage can occur with a fuel line blockage when the engine draws unfiltered fuel through the return line. It sure taught me a lesson about carelessly repurposing a 3-way valve!