Air in diesel supply - for 12 years!

[hans]

After many years of trouble with air in my diesel supply I approach the forum with my frustration. In 2000 we installed a Yanmar 3GM in our Monsun sailing boat (the old Hallberg Rassy 31). With this engine the boat has taken us on many good voyages in northern regions, including two trips to Spitsbergen and several sails across the North Sea from Frisian Islands in S to Shetland in N.

From the first season with the new engine we have had problems with air in the diesel supply whenever the boat had been idle for a few days. After venting it the engine would run without problems - until next start-up. This always seemed a problem in the beginning of the season only – after a few ventings the engine would start sweetly every time. The air-problem fluctuated from season to season: a couple of seasons the engine would stop while underway, needing venting before starting again.

I have had two different engineers look at the installation. We went through a series of attempts to find the source of the presumed air leak. We tried the trick of installing clear hoses to find an air leak, to no avail. We ran compressed air into the system, no leak found. Of course we have changed all the hoses, all clips, all brass washers. I have changed the cup for the fine filter on the engine, I have changed the diaphragm pump with built in mesh-filter. I have changed washers and bleed screw. I have changed from a CAV filter/water separator to a Racor filter – mostly because of the built in pump function. I have tried installing this filter/water separator at different heights. I have installed a day tank which feeds the diesel to the engine by gravity. Day tank is vented separately and venting is open. Return diesel goes to day tank.

After all these precautions I still find that whenever I change filters or bleed water from the water separator bowl, after a vigilent venting regime, there is air in the system again. Now I never let it get as far so the engine stalls, but my routine of having to bleed the filter/water separator and the fine filter on the engine after every day is messy and a hassle. After the engine has run for 40 – 50 hours there is no more air in the filter/water separator and I can relax my routines.

When I by-pass the Racor filter/water separator there is no air problem. So I have thought about removing this filter all together, relying on a filter/water separator between main tank and daytank only. As the day tank is quite large (40 litres) I would rather not, but I am getting a bit desperate. Does anybody have any suggestions? Any advice/suggestions greatly appreciated!

S/Y "Anna", currently Norwegian West coast

 

[Boo2]

When I by-pass the Racor filter/water separator there is no air problem.

It's faulty, replace it ? </Wild guess>

Boo2

 

[savageseadog]

Have a close look at the leak back system

 

[rotrax]

Our boat has an electric pump fitted before the Racor filter. After draining or changing a filter all that is required is to hold the pump switch down-about 30 seconds- untill the clicking becomes slow and steady. You and your engineer appear to have been carefull and correct in your investigations, and I am sure you are both aware that it is far easier for the fuel system to draw air than fuel. The leak could be anywhere from the tank outlet right up to the inlet of the high pressure side of the system. Every joint, union, connection and pipe must be suspect. An oil drain vacuum pump can be used to pull a vacuum in the system to check if it is drawing air. Disconnect the tank joint and seal it-a bolt up the flexible pipe and a hose clip perhaps-and fix the vacuum pump to the other end of the bit you need to test. When there is a good vacuum, close off the other end to keep it. I use a car brake pipe clamp for this. WD40 squirted on the joints may give you a clue as to where your fault lies as it will be sucked in. Another way is to pressurise the system and put soapy water on all the joints and unions. Bubbles will be seen where the high pressure escapes. Good Luck.

 

[jdc]

2 faults?

Hi Hans,

after you have done so many sensible things over such a long time I think any one will give advice only with trepidation and humility!

So I will only relate what I had as an issue, and hope that it may give you a clue. Our vaguely related symptom has been that after some days with the engine unused and with rough motion, ie under sail on long passages, the engine wont start until bled. The cause has never really been established because it sometimes doesn't recur for a year, so feedback 'loops' are rather slow. But I think I have finally found the cause and remedied it as follows: There is a primary cause which is a design fault of the boat builder (and I have a v high quality boat similar to an HR), but which one can get away with unless a very minor secondary fault occurs. Either would not cause trouble by itself.

The primary / underlying cause:
The lift from the tank (particularly bottom of the main tank, ie when the diesel is rather low) is quite a bit, approaching 75cm. This means that there is rather a vacuum on the Racor 110 primary filter when the engine is running, and on the Kubota secondary filter when the engine is off. Reading the manual for my Beta 2203 engine this installation should always have had an electric lift pump installed closer to the main tank, reducing the vacuum and making the installation easier to prime / bleed (I think this is what you mean by 'vent').

The secondary cause:
This is when the secondary filter has a small air leak. This has been due to two things; the filter itself not being quite straight so its large circular ring seal not being perfect, and/or the minute O ring in the bleeder screw being old (engineers _never_ replace these as a matter of course, although they should. Maybe it's because most don't know that such an O ring is there. CAV filters are particularly prone to this).

My solution to the primary cause is to install an electric lift pump (from FACET) quite low down near the tank. This means the filters are now under positive pressure, so minute air leaks don't matter (a) because diesel weeps out rather than air coming in, (b) diesel has much higher viscosity / surface tension than air anyway so it probably wont even seep out, and (c) many filters are designed with seals which are robust against positive pressure but poor against vacuum (which is why trying an air-line and soap bubbles is invariably a waste of time, or has been for me anyway).

So, with all due trepidation, have you considered an electric lift pump low down near the tank?

Best of luck anyway,
james

PS: My boat is currently in Bodø, so maybe we are quite close

 

[savageseadog]

I used to have a Peugeot 306 diesel that had fuel starvation problems. It didn't have a fuel pump and relied on the suction of the injector pump to draw fuel. It obviously worked for the most part but the slightest leak anywhere would cause problems. The Yanmar 3GM does have a fuel pump of course but a leak anywhere will allow air into the system as fuel flows back to the tank and that includes the leak back system.

 

[hans]

Thank you all for the useful feedback. I had hoped the daytank would have solved the suction problem - obviously not. If the problem persists an electric lift pump might be the way to go. I have agreed to have an engineer look at the installation while here in Florø. If the problem is still there i know I have a winter-project... Boat will winter at Otterøya by Molde, quite some distance from Bodø I am afraid.

 

[AntarcticPilot]

Boat will winter at Otterøya by Molde, quite some distance from Bodø I am afraid.

No help with your problem, but Molde is a lovely place; enjoy the roses! I spent a week in the Rica Seilet hotel, and the view from my window was amazing. Indeed, it almost compensated for being in closed meeting rooms most of the time

 

[ianj99]

Thank you all for the useful feedback. I had hoped the daytank would have solved the suction problem - obviously not. If the problem persists an electric lift pump might be the way to go. I have agreed to have an engineer look at the installation while here in Florø. If the problem is still there i know I have a winter-project... Boat will winter at Otterøya by Molde, quite some distance from Bodø I am afraid.

I had somewhat similar problems inherited from the previous owner. Replacing every seal in the system helped (especially those on the return pipes) but I fitted an electric lift pump level with the tank bottom a.nds moved the primary filter to the same level so it is gravity fed. The electric pump is between primary and seconday filters. No problems at all since and the electric pump makes bleeding the system after a filter change quick and easy.

 

[SOLARWIND]

Air in diesel

I too had a 12 year problem with air in diesel supply. The engine is a Volvo 2003. All of the system was replaced along with a hose that goes to the fuel lift pump. This new Volvo hose has a Bango fitting. On a whim I measured the Bango fitting and found that both sides of the Bango were not parallel letting air in at the copper washers.

The Volvo hose that I bought was different than the original in that it was not impervious to diesel. It smelled of diesel and the inside of the hose did not have metal shielding like the old one did but the metal crimp holding the fitting on the other end had VOLVO embossed on it.

It just happened that I kept the old Bango part that I took off and replaced it to an impervious hose and new fittings on the other end.

Problem solved.

 

[robbieg]

Fuel Return after injector pump

If you have a 2000 model GM you may have the system where fuel unused by the injector pump goes through a check valve and is then through a pipe to T into the return line from the injectors-see my post linked below on this subject.

http://www.ybw.com/forums/showthread.php?t=263105

If you have have a good look at this. I replaced and earlier GM with a 2002 model with this system and it was nothing but trouble. We replaced just about every component but it still had similar symptoms to you. Eventually I went back to the simpler system used on earlier models (ie no leak back system from the injector pump) and no more problems.

Hope this is of help.

 

[KellysEye]

I've said this many times before but put talcum powder around all fittings, where the bowl meets the filter, the lift pump, the bleed screw on the engine and anywhere else where diesel could leak. Leave it for at least twelve hours and if there is a leak you will see diesel in the powder. The usual reason for not finding a leak is that diesel will go through a microscopic hole that you can't see.

 

[pvb]

I've said this many times before but put talcum powder around all fittings, where the bowl meets the filter, the lift pump, the bleed screw on the engine and anywhere else where diesel could leak. Leave it for at least twelve hours and if there is a leak you will see diesel in the powder. The usual reason for not finding a leak is that diesel will go through a microscopic hole that you can't see.

He has air getting in, not diesel getting out!

 

[steve_l]

Does the water separator use an inverted glass bowl? Friend had one which had a small crack, just enough to let air through. Not so easy to see in the confines of the engine bay...

 

[ianat182]

Following on from Steve I's post; if your water separator is a two part one with a glass there may be a discrepancy between the sealing ring sizes for the upper and lower halves; again as mentioned above, perhaps an old sealing ring has not been removed from the grooves and the newer one installed over the old.

This is often a cause of oil leaks from the oil filter, particularly if in a confined engine space
with limited visibilty of the mounting.

ianat182

 

[KellysEye]

>He has air getting in, not diesel getting out!

If a joint etc is leaking diesel will get out and air will get in. If he tries the talcum powder and has a leak he will find it. A forum member has already found an air in/diesel out leak doing that.

 

[rotrax]

>He has air getting in, not diesel getting out!

If a joint etc is leaking diesel will get out and air will get in. If he tries the talcum powder and has a leak he will find it. A forum member has already found an air in/diesel out leak doing that.

Quite. While the fuel is flowing the air is drawn in. When the engine is stopped, often talc or similar will show diesel leaking out, albeit in minute quantities.

 

[pvb]

If a joint etc is leaking diesel will get out and air will get in. If he tries the talcum powder and has a leak he will find it. A forum member has already found an air in/diesel out leak doing that.

No, if the tank is lower than the engine, diesel won't leak out.

 

[KellysEye]

>No, if the tank is lower than the engine, diesel won't leak out.

Incorrect, our tank is lower than the engine and we had many air/disel leaks when we had copper piping, which I changed because of the leaks. If you think about it the filter is full up with diesel and the inlets/oulets are slightly lower than the top of the filter, hence the fittings can leak.

 

[pvb]

Incorrect, our tank is lower than the engine and we had many air/disel leaks when we had copper piping, which I changed because of the leaks. If you think about it the filter is full up with diesel and the inlets/oulets are slightly lower than the top of the filter, hence the fittings can leak.

Well, that's certainly not my experience with a keel tank and CAV-type filters (which incidentally seem to have the inlet and outlet higher than the top of the filter element).