Fuel/Engine Problems - Again!!!

[dauntlessman]

Hello people,

I placed a thread a couple of weeks ago following a recent diesel engine problem. The engine lost revs/power after half an hour and eventually conked out. It was eventually put down to a sludged up tank and blocked filter with the possibility of water getting into the system.

Anyway I replaced the filter, renewed the fuel and added some diesel bug treatment. I also filled the tank to capacity with petrol station diesel to prevent condensation build up. All was well and we have just enjoyed an excellent couple of days sailing. Then about 500 yards from the mooring, exactly the same. This time the engine didn't take much time to die at around 15 seconds of choking.

I had been told that the diesel bug would break the sludge down and I may need to do another filter change after a run in. Bearing this in mind I had a few spares so grabbed a mooring and set about changing the filter again. When I took the filter out (only been in their for a few days), it looked pretty much brand new with no sludge at all. The water trap also looked completely free of water. So I have now put it all back together again (with another new filter just in case), bled the system and once again; running fine.

This is frustrating as I can't get my head around the problem. The fuel seems clean and the tank free from water. A guy in my local yard suggested another explanation which you may be able to help with. He has suggested that the fuel breather pipe may be blocked and there may be a lack of air in the tank, particularly after a half hour (or longer) run and that this could be the problem. It has been suggested that the problem would be made much worse with a full tank of fuel, hence it only taking 15 seconds to die.

On inspection of the tank (I have not had the boat long) I have come to the conclusion that there is no fuel breather at all!

Is this be the problem?

 

[cliff]

Possible but the easy way to check is run the engine again ubtil it chokes then open the fuel filler cap. If you hear the air rushing in and/or the engine starts after removong the filler then it would tend to indicate that is your problem. Be careful you don't draw any air into the feed lines as the engine chokes or you will need to bleed the system again.

I am surprised there is no breather on the tank - could it be in the filler cap and blocked?
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"Artificial intelligence is no match for natural stupidity"

 

[dauntlessman]

Hi Cliff. Thanks, I think removing the cap when it starts struggling again will be my next test. I seriously cannot see a breather anywhere on the engine and I'm sure it's not part of the cap which looks pre-historic.

Mind you I am thinking of drilling a small hole into the cap and securing some kind of bent pipe should this prove to be the problem.

What sort of diameter does this pipe need to be do you think? The tank looks pretty small in capacity.

 

[cliff]

To act as a vent not very big, but for mechanical strength 6mm or 8mm should be enough IMHO.
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"Artificial intelligence is no match for natural stupidity"

 

[Marsupial]

Hi Dauntlessman

I have had a similar experience, engine stops remove filters all ok, bleed the engine all ok but still thw thing wont run for more than a few seconds etc. is very frustrating. . on TWO occasions in different boats the problem was a blocked fuel pipe in the elbow/bend at the top of the dip tube - the second one took only minutes to solve - after the filters were checked, the first one took a few beers longer!

Its worth a try

Cheers


David

 

[Heckler]

i agree, if you check the feed pipe from the tank some of them have gauze on the end which gets plugged with the goo. also you can get floaty bits which jam against the end, the bit about blocked breathers on the tank is a one that peeps go on about but in 40 years of repairing plant and vehicules i have come across it once, the breather on my bene tank is about 1/2" and would take a lot to block it, in my opinion its a red herring.
be logical, if filters are not blocked, and believe me you can see when a filter is blocked then look for a blocked feed pipe first especially if you have a stack pipe in the tank.

 

[Anonymous]

I've never noticed a breather on any boat I have had, either, and never had a problem. Firstly, though, don't forget that a diesel circulates much more fuel than it used - excess fuel from the injectors is returned either to the tank or the filter.

I have my doubts about the need to drill a hole; this isn't a new boat so why is it needed now? A hole can also let in water so is best avoided.

Certainly the problem sounds like fuel starvation but it could just as easily be due to air being introduced into the system. The classic place is in the low pressure fuel pump - maybe the diagphram is holed?

 

[alant]

You may have a tank breather you haven't noticed.
Fill the tank until it either reaches the top of the filler, or you discover the breather overflowing elsewhere.
My car is diesel & when I take the filler cap off, I get air sucked in, so perhaps this 'negative pressure' check alone, might not indicate lack of breather.

 

[TheBoatman]

Alex
First off your tank must be able to breath - you can't fill a tank then seal it complete and then try and suck the contents out either the engine will stop or the tank will collapse in on itself.
Has for the size of hole needed, last year I fitted a 100 ltr petrol tank to a rib and drilled a 1mm hole to let it breath - works just fine but I did drill it were water could not enter.

As suggested what you could do is "loosen" the tank filler cap and drive the boat at 3/4 throttle for a long period and see if it stops on you. If it doesn't then do the cap up and try the same thing and if the engine stops it's a breather problem simply solved by drilling a hole somewhere to allow it to breath.

BTW my hole is drilled in the first part of the down pipe on the filler cap so that there's no chance of fuel slopping out.

Peter.

 

[Sui Generis]

Agreed - that is where I would start looking. Otherwise, collapsed/ delaminated flexible fuel lines? Just doesn't ring right that the breather (or lack of) would stop the engine within 500m of the mooring.

Dauntlessman, please don't think I'm trying to make you suck eggs, but it has served me well in the past in this situation, think simplistically and start at the beginning of the system and work methodically through it.

I didn't see your original thread, but was it definately down to diesel bug and a sludged tank - or could you have an air leak - perhaps through porous flexible rubber fuel lines?

 

[cliff]

[ QUOTE ]
All was well and we have just enjoyed an excellent couple of days sailing. Then about 500 yards from the mooring, exactly the same. This time the engine didn't take much time to die at around 15 seconds of choking.

[/ QUOTE ].

He had a couple of days sailing then the motor died on the way back to the mooring as I read it.

If the tank was full it would not take the draw of much fuel to create a partial vacuum in the tank sufficient to stop the engine.

If running without the filler cap results in the same problem then the next logical place to look is the pickup pipe and tubing between the engine and the filter.

Remember all rigid fuel tanks must have a "breather" of some sort otherwise the tank would tend to collapse on itself as fuel was drawn off.

Many years ago I was on a crew repairing war damage in a refinery / tank farm. The fuel tanks had been collapsed by shutting the breathers on the top and draining off the fuel. Atmospheric pressure did the rest.

Certainly the whole fuel system may need looked at but let's check the easy items first. I have lost count of the number of times so called "experts" have torn equipment apart looking for a problem only to find the problem was something that was easy to check, needed little or no dismantling and if checked first would have saved days of downtime.

Golden rule when trouble shooting a problem is start with the obvious and easily checked causes and rule them out, then look for the less obvious causes.
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"Artificial intelligence is no match for natural stupidity"

 

[savageseadog]

I had a problem like this on a diesel plant. It was caused by a small piece of polythene being sucked onto the outlet.

 

[jfkal]

Did you replace the secondary filter at the engine. The clog may be there now.

 

[Guest]

Some tanks breathe via the filler .... such as with a car ...

Mine has a small pipe that runs up side of filler pipe and then to a nylon fitting in cabin side.

A way to check if you are creating a vacuum is to run engine till it conks out - quickly - I mean immediately open filler cap - if its hard to undo or you hear a hiss as you unscrew - bobs the proverbial.


Sounds perfectly feasible.

 

[rob2]

I had similar symptoms when collecting my new boat last year. It turned out to be air sucked in through the fuel lines. The ends had started to decompose under the jubilee clips. Cutting a small piece off each end to reach good material and remaking the joints has kept her running ever since.
Best of luck in your search. I am taking the safe option now and replacing all the fuel lines.

 

[dauntlessman]

Ok guys, thanks for your help on this one. I'm going to go down to the boat tonight armed with some brand new fuel hose. I may also try and shorten the length from tank to pump, as it seems unnecessarily long at the moment. It could well be gunge blocked in a gauze at the tank end (though I won't know until I whip out the old pipe).

One of my problems here is that this is a very old wooden boat, which has recently been restored (though I don't think the engine/tank received the same TLC as the rest of the boat)! Consequently, there is a lot of would glued around the tank which would make removal a pretty big deal.

Given that the low-pressure part of the system is gravity fed, how much of a problem will I have trying to replace the primary hose (attached to the bottom of the tank) when the tank is completely full of fuel? Obviously I would prefer it not to be pissing out all over the place). Perhaps I can temporarily plug it until the new hose is ready to go in.

In answer to another question. This old 8HP single cylinder only has one (primary) filter. If I replace the fuel line, would you advise installing another filter, even if it were just a small inline type?

 

[davidpbo]

I don't know whether this option was covered in your previous thread.

I had a problem with a diesel engine in my car, I think after I had painted the fuel tank. It would start, run for a while then stop. Transpired it was a pin hole in the fuel uplift pipe allowing air to be sucked in. I verified the presence of a hole by 1) there was some fuel escaping from it. 2) I disconnected all the pipes, capped them with polythene bags tied on with cable ties and pressurised the tank slightly with a tyre compressor and listened for air escaping, some washing up liquid on the area it seemed to be coming from confirmed the leak. It was impossible to repair the tank so replaced it, no problem since.

David

 

[davidpbo]

IMHO If you do not have a fuel shut off tap under the tank draining the tank should be seriously consider.

Sorry missed the previous post on air in fuel system.

David

 

[Tomkat17]

I read somewhere recently about someone with a similar problem who found that there was a small in-line filter on his fuel line upstream of his primary fuel filter, which was partially blocked.

 

[duncan]

experience (three years and counting) says that you simply aren't going to 'clean sludge out of a tank' using fuel additives. If you have some biomass from a bug attack then OK but not 'real sludge'.

Clean filter but same problem (after blocked sludgy filter) says blockage back to the tank (as other have said). This can be either at the pick up point (gauze or not) or at any restriction including 90 bends at the top of a pick up pipe. If you hadn't had badly blocked filters recently then possibly diaphram pump problem etc but right now I would put it low down on the list.

I would start with the pick up pipe, not forgettign to blow through the fuel pipe between it and the engine as well.

If you can put a thin pipe or rod down through the hole where the pick up pipe has been removed to the bottom of the tank you shold be able to establish the nature of your sludge (feel and sound) - even better is one of the perla oil change pumps which have a tube that will fit and you can suck up through it. Unfortunately if you do have a problem it's diameter is too small to be able to hoover up the crap. Quite frankly I would simply replace the tank - it will be easier in the long run!

Good luck