Try finding an Air leak?

Caer Urfa

Caer Urfa

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Re-newed all my diesel fuel system to twin tanks 4 months ago, all new filters, pipework, valves, cleaned tanks etc.
Engine has now ran twice for totaly approximatly 12/14 hrs in between sailing then shuts down. No signs of water in Glass filters.
Diesel from good marina regular supplier with no problems to me or others before will run trouble free for another 12/14 hrs and then shuts down again!
Checked all the hose clips and nuts etc.
No sign's of diesel leakage anywhere, we all conclude the engine must be 'sucking in air 'somewhere.
Been out in rough & calmer seas no problems.
One says just bleed it everytime I come back!
Another says no as you will never know if you have cured the leak and should not have to keep re-bleeding the engine, All easy to say except when the engine shuts down as you are entering a lock or passing close by to rocks !.
Any other suggestions of what to try or where to look will be gratfully recieved.
 
Take the fuel outlet off the tank and blow down it. Look for air leaks with soapy solution. You might have debris in the tanks or a split in the fuel pump diaphram.
 
If it was an air leak I'd have thought it would either fail more quickly or you'd notice signs of fuel starvation.

You don't mention how quickly it shuts down, but I can't work out how an air leak would cause a problem after 12 hours without some warning.

Maybe you have debris in the system which is blocking the fuel flow randomly? If you open a bleed valve and get air sucked in that would suggest you have a blockage upstream of the valve.

The previous poster's idea of a pressure test sounds good to me, but assuming that fails, as I suspect it will, I'd think about where debris might be causing a blockage.

And finally, the obvious point, you have got some way to get air back into the tanks? My outboard conked out at night in Bonaire some months ago and I was contemplating whether I'd be able to steer to Curacao (only 30 odd miles away) or would drift all the way to Colombia if no one picked up my alerts when I thought "hmm, wonder if I opened the air vent?".

A friend of mine likes to put an outboard-tank style primer bulb in his diesel system to assist priming. This also has the advantage of revealing if there is a partial vacuum in the system. Rigging something like that up, even temporarily, might help figure out what's going on.

Good luck, and let us know the solution when you find it!
 
Some years ago a friend had a similar problem with a new tank.
The solution was finally found to be a price tag floating around inside. It would cover the end of the fuel pipe until the engine stopped. Once the suction had gone it floated away again until the engine was restarted.
 
When was the tank last cleaned? I had a similar problem which dissappeared when I emptied the tank, disconnected the outlet hose and gave it a good scrubbing before running through some fuel which I later disposed of. Have you an in line coarse fuel filter fitted? If so I would dismantle and examine for dirt. And then replace if required. Always carry a spare. I presume you are bleeding the engine yourself? (if not you should learn how to). It shouldn't really be too big a deal, particularly if you have the right size tools ready to hand.
 
I had a similar problem at the beginning of the season and dismantled and re- assembled everything after removing and cleaning the tank. Then I did it again and again but with the same problem - the engine would start and then cut out - on re-starting it would run and then cut out after around 5 mins.
I could only think of two weakenesses - firstly at the tank connection, and secondly at the bolt holding the glass water separator, so I bought a tube of Red Stag and gave them both a dollop - job's a good 'un
 
First of all both tanks were removed and completely cleaned four month ago, and All pipework and fitting are new.
The new system is I can run off either tank, (or both) and send fuel return to either tank or both also can change either filter at sea if engine is still running.
All pipework is 3/8" bore.
Boat is as you see motorsailor used offshore in 'all weather', no chance of anything in tanks or pipework.
Both tanks by Tec Tank.
Interesting point made on post about re-sealing filter assembly, will look at that.
Thanks for replies so far.
Mike
 
Change over valves have been the cause of leaks in the past. eradicate this for a period, and run direct connection, see if the problem persists. then start taping into the system at different points working away from engine, until you find the source of the proble.
 
I also sought views on the forum and at my Club, and was also advised that the water separator and filter seal were the most likely causes so I renewed the filter (again) and took the water separator off completely as a unit and then dismantled and re-assembled it on the bench, but all to no avail. I guess that the pressure test is the only certain route. In my case I was able to identify two possible weak links and cured one or both of them.

Best of luck - I know how frustrating it is
 
I also had this problem after installing a new engine, tank and all new fuel lines. Worked fine for the first 50 hours then would stop; it would restart but only for a few seconds before stoping again. I retightened all the unions and joints, changed the filter and it still happened only this time it would run for 15-20 minutes before stopping. In desperation(we were in Holland at the time) I rang the Beta engineer and he agreed with my diagnosis of air getting in somewhere, check all the unions etc but also when engine running to just crack each injector in turn to get rid of any air in the injector - apparently the Beta is prone to this. Done as he suggested and it's been fine eversince.
 
Are the tanks below the level of the engine - presumably they are? Is the lift pump OK or is there a pin hole in the diaphragm? Would it be possible for you to jury rig a day tank in the cockpit (or somewhere above the level of the engine) and try running on that for a few days?
 
Check the entire system using a combination pressure/vacuum gauge. Disconnect the piping starting at the motor and working back towards the fuel tank. Reconnect each piping sections as you eliminate that area. This will definitely tell you is there is an air leak on the intake or pressure side of the pump(s)
 
I would agree with the pressure testing suggestion, from the engine back to the tank.

I had the same problem with a Beta, it would run for hours then stop. Checked and rechecked the system with no result.

Finally, with the help of a mechanically minded pal connected a foot pump to the engine end. Turned out there was a tiny air leak in the O ring of the primary filter.

The engine has run perfectly since then.

Good luck
 
Thanks to all for the suggestions.
If I disconnect the main feed pipe from the tanks (above the engine by the way) into the primary filters THEN pressure test do I leave the Diesel in the filters?or do I need to empty them first?
If I connect a bicycle pump to pressurise the filters intake connection and use soapy water do you think this will be a good test?
Also I do have a 'three way' changeover valve so I can run off both tanks, or port, or starboard tank
I have looked carefully for signs of a diesel leak but I am told that just because air can suck 'in' diesel does not always have to leak 'out'!
 
Do you have a tap/valve/cutoff between the tank and the primary filter?
If so. close it and then connect the pump at the engine end.

Then pressurise the fuel line from the engine side of the secondary filter to the tank side of the primary

Hopefully once the diesel in the fuel line has some pressure behind it any leak will become more apparent
Good luck
 
Still a little bit confused here. I thought modern diesel engines were self purging, and so would remove any air that was entrained by a leak between the tank and the engine. I know that when an engine stops, you have to run around and set sails etc, but I think one useful test would be to crack one injection point and then crank the engine. If no diesel comes out then the airlock theory holds, but if diesel comes out after a bit of cranking then an air leak is to blame. On the latter you can pressure test from inlet to diesel pump primary filter backwards to the tankage and taps etc. If that does not work it must the the primary filter seal.
If you use a car footpump with pressure gauge, you should be able to pressure to 5-10 psi and watch the gauge fall. Luckily 3/8 pipe will fit the end of the valve adaptor on the footpump, so you should get an airtight fit.
 
Will try pressurising it.
Only thing I can think of is the Glass bowled primary filters themselves, secondry filter or the three way change over valve, but when I fitted any threaded connections I sealed them with 'Rocol oil seal' all others have new SS Jubilee clips.

THANKS TO EVERYONE FOR ALL THE ADVICE !
 
I have not read all of the replies but I'd guess you are doing so. You've got lots of ill informed guess work going on - typical of this forum.

Most likely its air as you surmise and it will be independant of all of the variable suggested. Air can enter a fuel system in such small quatities per minute that even transparant pipework will not make air bubbles visible, but the will collect at some high point until the volume of air cause the engine to stop. Such it was in my case but the engine ran for about 12 hours before stopping. (note sail boat using 3 L/Hr) The air can only enter via joints and punctures where the pressure in the pipe is below ambient i.e. the air is sucked in. Chances are this will be earlier than the lift pump because after it the system will have positive pressure. So check all joints before the lift pump, and include the lift pump. Some had so many gaskets they leaked by design. Good luck. It took us a whole week to find the air leak when we had one.
 
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