Bleeding Problem

[Winf]

Hi all,

Had a small drama yesterday when entering leads to our proposed anchorage, the motor cut out. Engine is a Yanmar 3HM 30hp. No previous issues and ran smoothly earlier in the day when leaving port.

Sea state was very rolly and I suspected that I sucked some air in the line from the tank although the tank was approx 70% full. I noticed some air at the top of the feed line from the tank to the filter/ separator and some air at the top of the glass bowl.

Got the sails up to get some sea room, bled the line, motor restarted ok and we got in safely.

After bleeding though, I could still see air at the top of the fuel line from the tank to the filter and some air at the top of the glass bowl so was not feeling overly comfortable on the way in.

Today, at anchor I have filled the tank up to the brim and tried to bleed this remaining air out to no avail. What am I doing wrong here?

Setup is as follows:

1. Tank is stainless, approx 100 litres and is located under stbd quarter berth. Is an odd shape to follow hull shape, shallow outboard (approx 100mm) deepest inboard.

2. Tank was completely cleaned out a couple of months ago and a diesel tank sealer applied to the inside to correct some pinhole leaks. Seems to have worked with no leaks observed.

3. Fuel line from the tank is at the bottom ie lowest point of the tank.

4. Fuel line goes from tank to the inlet port of a Lucas Cav filter/separator. Filter was changed after the tank was cleaned and resealed. Less than 30 hours operation since then.

5. Outlet from filter assembly goes to an electric pump (looks like an addition, by a previous owner) and outlet of electric pump goes to the Yanmar fuel feed pump mounted on the motor.

6. Filter assembly is above the level of the tank.

7. The manual priming lever of the fuel feed pump does not work. To bleed, I switch ignition on, electric pump starts, crack the bleed nut on the secondary fuel strainer on the motor and wait till I get a clean flow.

I have done this and the engine starts and runs fine at idle, at full revs and at full revs under load. But I can still see air at the top of the fuel line (just as it enters the filter assy) and there are a few bubbles at the top of the glass on the filter assy. I have never noticed this before and it has got me tossed and concerned that an unplanned failure will happen again.

How do I get this air out or am I good to go?

Any assistance appreciated.

Regards

Winf

[NoTies]

Your life would be a lot better if you relocated the electric lift pump to between the tank outlet and the CAV filter. This type of filter are a right sod to exclude all the air from if on the suction side of the pump. I'm guessing you got a dollop of air from it with all the rolling. It constantly amazes me the bad design of most primary filter installations. It also amazes me that all engine manufacturers recommend a primary filter but don't fit the bloody things as standard. Properly engineered that would remove so many of the bleeding problems on boats.

[sanibel sailor]

Other possibility is a clogged filter-from leak stopper, causing high vac pressure. I would swap it out. Have you got clear fuel hose, how can you see air in the line?

[Winf]

Originally Posted by sanibel sailor

Other possibility is a clogged filter-from leak stopper, causing high vac pressure. I would swap it out. Have you got clear fuel hose, how can you see air in the line?

Yes, hose is clear so can see the air. Thought about the possibility of a clogged filter. Will check/change it out as soon as I can to eliminate it from the equation but can't understand how a clogged filter would cause air to be in the line?

Ran the engine again this afternoon for a good 5-10 minutes at idle and maximum revs and didn't miss a beat. Can still see the air though.

Re pump on the other side of the filter, I thought the idea was to only put filtered fuel through the pump hence install downstream of the filter?

Winf

[AnchorageGuy]

Winf, If you put the electric fuel pump before the filter, you can pretty much guarantee more problems. The electric pump will wind up clogged because nothing is protecting it. You are getting air into the lines, so the first thing to check is the fittings and hose clamps. Even though you don't see fuel leaks, air can get in. If the pick up tube screws into a fitting on the inside of the tank, start there. I use Permatex aircraft rated sealant for all of my fuel fittings. Start there before making modifications to the system. Sorry if this is a stupid question, but you do run the fuel pump when the engine is running don't you? Chuck

[Winf]

Thanks Chuck re pump location, that was what I thought.

Yes, pump runs all the time engine runs. It switches on with the ignition key.

I have checked all the hose clamps I can reach except for the one at the outlet on the tank. Access is very tough for that one and this crap anchorage rolling us around is not going to make it an easy one to get to. The fuel line is clamped onto a pipe stub from the tank and from there it is straight to the filter inlet. Nil other connections

Why does the thing run so well though? I always thought slightest bit of air and a diesel snuffs.

Winf

[AnchorageGuy]

Winf, If the air pocket stays in the same place it won't affect the engine running. But as soon as it moves into the injector pump, it will stall. That will happen in rough weather or seas. The one fitting you can't get to will always be the one that is the problem. Chuck

[Winf]

Originally Posted by AnchorageGuy

The one fitting you can't get to will always be the one that is the problem. Chuck

Ain't it always so! Will have another look in the morning. Time for some sleep. Thanks.

Winf

[NoTies]

Originally Posted by AnchorageGuy

Winf, If you put the electric fuel pump before the filter, you can pretty much guarantee more problems. The electric pump will wind up clogged because nothing is protecting it. You are getting air into the lines, so the first thing to check is the fittings and hose clamps. Even though you don't see fuel leaks, air can get in. If the pick up tube screws into a fitting on the inside of the tank, start there. I use Permatex aircraft rated sealant for all of my fuel fittings. Start there before making modifications to the system. Sorry if this is a stupid question, but you do run the fuel pump when the engine is running don't you? Chuck

Every electric fuel pump of quality I have ever seen has a screen on the inlet side to protect the pump. If you can tell me how to successfully exclude all air from a CAV filter that is mounted higher than the tank with the priming pump mounted after the filter then I will be eternally grateful.

[AnchorageGuy]

Originally Posted by NoTies

Every electric fuel pump of quality I have ever seen has a screen on the inlet side to protect the pump. If you can tell me how to successfully exclude all air from a CAV filter that is mounted higher than the tank with the priming pump mounted after the filter then I will be eternally grateful.

That screen is exactly what will clog up in a heartbeat if the pump is located before the filter. The CAV filter is typically mounted on the engine and is in fact a secondary filter on most engines I have worked on in the last 40 years. In that time I have changed thousands of fuel filters and had to bleed as many engines. The primary is usually a Racor putting the pump between the primary and the CAV filter. I have on occasion seen only a CAV filter on smaller diesels, but not very often. Chuck

[NoTies]

Point 4 of the OP

[Winf]

Ok here is the latest and thanks for

Changed the filter this morning. Couple of bits of crud in the top of the filter but nothing significant.

New filter installed, bled line and still this small amount of air in the line from the tank to the filter visible at the connection to the filter.

This filter is the primary filter. Fuel goes from tank direct to this filter.

Renewed all connections on the filter. Ran the motor at idle for probably half an hour or more. No change, can still see the air.

I can easily remove the filter from its mount on the engine bay door so did this and "simulated" wave action moving the filter to and fro, back and forth etc. Engine purred along. Did the same at about cruising revs and same result. Did this for half an hour or so. Engine purred along.

Used soap bubbles on all connections on the filter to see if I could spot an area sucking in air but nothing. But I can still see this damn air bubble and it is driving me nuts frying to figure it out.

I looked very carefully at the line from the tank to the filter and can see no bubbles travelling up the fuel line from the tank connection. If I tip the filter so that the air bubble must rise, hold it there for a minute, and then bring the filter back to level, the bubble disappears for a minute or so but then it is back.

Winf

[scotty c-m]

Are all the seals and fittings of the fuel filter itself tight and in good condition? Also, does the filter have a bleed nob at the top?

[Winf]

Originally Posted by scotty c-m

Are all the seals and fittings of the fuel filter itself tight and in good condition? Also, does the filter have a bleed nob at the top?

Fuel filter is new. All seals new. Fittings all look good and are tight. There is a bleed nut at the top.

This afternoon I have lowered the filter assy by 4-5 inches though it is still higher than the level of the top of the tank by 4-5 inches.

Replaced line between filter outlet and electric fuel pump inlet.

Replaced line between pump outlet and the feed pump inlet.

Relocated the electric fuel pump for easier access and so bit marked "top" is now on uppermost.

Bled line, started engine, bled it some more and still there is air! Swore some. Time for a break. What am I missing here?

Winf

[MBWhite]

I am not saying this is the perfect solution to the issue, but at this point I would most likely disconnect the fuel line between the electric pump and the yanmar lift pump and just let the electric pump run for several minutes to see if the extra velocity can get your bubbles out. You can just feed it back into the tank or let it run into a container so you can inspect it before pouring it back into the tank.

Is the tank vented, and is the vent free? Also, if a person gets desperate enough about finding a vacuum leak you can figure out how to pressurise the tank with about 5 lbs of air and see if the leak can show up under pressure. You can also paint any suspect flanges from the outside with a liquid sealant if you think it might have a vacuum leak, but it will usually look like a half assed repair but is worth keeping in your bag of tricks anyway. But I'd try running the electric pump for a while first to get all the air out and then see if it reoccurs.