Yanmar - need to bleed air after two days nonuse

[Bay Pelican]

Looking for things to check. Bay Pelican has a 27 hp Yanmar as a backup engine. Worked wonderfully until last year when I installed a separate 12 US gallon diesel tank and new Racor filter so that the engine was totally isolated from the main engine and its fuel supply.

The tank I installed was a decent brand 12 gallon tank with a top feed, typical Racor 500 series, new 5/16" fuel lines.n While the fuel line approaches the engine from below the fuel pump and thus diesel could drain down this is the same arrangement as before.

Now every time the engine sits I have to bleed air from the engine to get it started. A slight amount of air collects after the fuel pump at the location of the second bleed screw right before the injection pump.

I have tightened all fittings. I have checked the seal on the Racor. Tightened the bleed screws on the Yanmar (there are two).

The 12 gallon tank while it is a top feed is above the level of the Yanmar's fuel pump, as is the Racor. The old tank feed was from the bottom of Bay Pelican's fuel tanks and thus there was pressure from the weight of the fuel.

My next approach is to connect the current Racor to one of Bay Pelican's bottom feed fuel tanks directly and not use the new tank and see if that changes anything. If that doesn't work I will bypass the Racor and see if it is the problem (anything is possible.)

Wondering if the Yanmar fuel system is such that there is a slow leak of air and the fuel is draining back to the tank or the Racor.

Another approach I am thinking of is raising the last 12 inches of the fuel hose above the fuel pump so that that fuel drains down and puts pressure on the fuel pump.

Any other things to check or suggestions would be appreciated.

 

[LarryM]

My next approach is to connect the current Racor to one of Bay Pelican's bottom feed fuel tanks directly and not use the new tank and see if that changes anything. If that doesn't work I will bypass the Racor and see if it is the problem (anything is possible.)

Wondering if the Yanmar fuel system is such that there is a slow leak of air and the fuel is draining back to the tank or the Racor.

Marty,

Obviously you have a small air leak somewhere and your approach to troubleshooting it sounds right. I have been around and owned several smaller Yanmar diesels (18-100 hp) with both top and bottom-fed tanks and Racor 500 filters. No configuration was any more troublesome than the other.

The factory installation manuals reference tanks located both above and below the level of the lift pump, the only requirement being that they be located within the suction head capacity of the pump if located below it.

The mechanical lift pumps are pretty durable, but I did have to replace one once that was exhibiting a problem like yours due to a ruptured diaphragm.

Sounds like you will find it pretty quickly using your troubleshooting process. Re-connecting to the original supply source is definitely where to start, particularly if nothing downstream of that connection has been changed or disturbed. Oh, a handful of new copper crush washers of the appropriate size for bleed screws and banjo fittings might be in order.

Good luck

 

[Ski in NC]

One trick is to temporarily replace your suction and return lines with clear vinyl hose. Prime up and run engine, then observe hoses and see where the air is coming from. Tracking down tiny air leaks in fuel systems is a PITA.

 

[LarryM]

One trick is to temporarily replace your suction and return lines with clear vinyl hose. Prime up and run engine, then observe hoses and see where the air is coming from. Tracking down tiny air leaks in fuel systems is a PITA.

That's a great tip. I once saw that method used on a old Volvo diesel that had defied everything else. In fact, it took a full day to actually see any bubbles accumulate. The wise old mechanic that showed me that trick told me to be sure to put a loop or hump in the line so that any smaller or emulsified bubbles could accumulate in the clear tube. I had completely forgotten that one.

 

[Xsbank]

If the bleed screws have copper washers, either replace them or anneal the old ones. They get rock hard and it's very difficult to get a seal.

 

[FlyWright]

Do you have an engine mounted filter? Last time I did my filters, I had a small air leak in one engine secondary...not enough to leak fuel, but enough to let air in when idle. Same symptoms. The seal was very slightly pinched in the seat.

 

[bayview]

look for any fuel weeping with the system pressurized while running.

 

[boatpoker]

I had a similar problem years ago. I taped paper towel around every junction in the fuel system and waited until one got wet. Also found a very small leak in my potable water system with same method.

 

[Bay Pelican]

Many thanks. Working on several of the suggestions.

 

[Bay Pelican]

Follow up. It appears I have solved what should have been a very easy problem to fix. The feed hose from the Racor to the engine is 6 feet long and is 5/16" - small. When I replaced the hose with a clear hose it was obvious that manually filling the hose left several air pockets in the feed line. I had been using a funnel. After seeing the air bubbles I was able to work them out of the clear hose and the engine worked very well. Since I couldn't see the air bubbles in the regular fuel hose and thus could not work them out manually, I attached the hose to my fuel polishing pump and pushed fuel through the hose to a bucket. Engine appears to be starting and running well.

 

[Bay Pelican]

I have continued to work on this problem. The Yanmar will need to be bled if I let the engine set for two days. However if I close the ball valve between the fuel tank and the Racor after using the engine and then open the ball valve right before using the engine the engine will start and run.

Looking for an explanation and whether this means the leak is in the fuel tank and its fittings or is it just that with the ball valve open the suction pulls the fuel back into the tank because of an air link between the ball valve and the engine?

Any thoughts?

 

[Wxx3]

Top or bottom feed?

Sounds like it must be top feed, then there is the problem.

 

[Capt.Bill11]

Perhaps you have a bad fuel check valve? Or need to add one now that you changed the style of tank feed.

I assume you have tightened all the fuel line connections and checked the seals on the Racor. Have you actually removed, cleaned and resealed the fuel connections as well at this point?

 

[Palmbeachphil]

The leak is behind the valve or the valve itself. I had a stopcock valve with a crack which which too me forever to diagnosis. Eliminate this valve in your set p and try.

 

[Bay Pelican]

It is a mueller 12 gallon tank with a top feed. Put this in so it would be independent of the main fuel supply.

Yes everything has been tightened from the ball valve to the engine. Hose clamps replaced. Washers on Banjo bolts and bleed screws replaced.

 

[AusCan]

It could possibly be a slight leak at the connection between the plastic pickup tube and the top elbow on your top feed tank fitting. You'd have to remove the fitting from the tank to check it.

 

[Capt.Bill11]

Run a fuel line right from the first connection at the tank directly to the genset bypassing everything else that's new and see what happens.

 

[LarryM]

Run a fuel line right from the first connection at the tank directly to the genset bypassing everything else that's new and see what happens.

And make it clear tubing so you can spot any air in the system, and which direction it is migrating to/from.

If that is leak free, then re-plumb using the clear tubing in every segment of the system and observe again. Something is bound to become visible at some point.

If the Racor is new, it is possible, but not very likely that you could have a leak around the cover or one of the threaded fittings. There is also an internal ball check valve and seat that could be leaking.

Finally, here is some info from Yanmar and Racor on the fuel system and filter installation. I also included a breakdown that shows the internal check valve.

Hope that helps. Good luck.

 

[Bay Pelican]

Many thank to all for the suggestions. It gives me something to work on over the next week.

 

[Rogerh]

I was going to mention the checkvalve in the Racor that Larry talked about. If this is not a new Racor and has been rebuilt it is possible that the seat for the ball valve was installed upside down. Refer to the link from Compass on the rebuild of Racors. Rebuilding A Racor Turbine Filter Photo Gallery by Compass Marine How To at pbase.com

 

[chester613]

Just for giggles, check the fuel lines on the engine carefully. There is a filter on the engine after the Racor. The inlet and return can be reversed and the engine would still run. But, it will get starved for fuel after a while. A small engine like that will go for quite a while. I have done this, that's why I know. I did it on a 44 HP Yanmar and couldn't figure out why I couldn't run for more than 20 minutes or so. I actually installed an electric fuel pump, thinking it was the mechanical pump that was tired. Then a mechanic friend of mine was on my boat and was looking at it. In about 30 seconds, he switched the fuel lines top and bottom and all was right with the world. Just a thought. On mine, the intake went to the bottom and the return was on top. To me, I just hooked it up the way I thought it should go. Intake at the top, return at the bottom.

 

[Bay Pelican]

Once started the engine will run without stopping. When we moved the boat I let the Yanmar run for an hour. Will confirm fuel line arrangements.

 

[FlyWright]

Many thank to all for the suggestions. It gives me something to work on over the next week.

If you fly me down there, I'll lend a hand and moral support, Marty! I'm wide open next week!!

 

[eyschulman]

If nothing else works what about a small in line electric fuel pump or an isolated loop out board motor fuel bulb pump as used in the Seaboard fuel system(see Seaboard site on net)

 

[Flatsflyer]

fuel leak detection

Many thanks. Working on several of the suggestions.

Use baby Powder, rub it on all fitting and watch for the leak, works every time.

 

[cappy208]

I have a similar installation on my vessel. An ordinary auto fuel pump (inline) which is keyed on when the ignition is on is the key when I do filter changes. Running it and purging all the air out is key. I have not determined if the pump was installed because of a low performing fuel pump, or the fact that the filters are above the level of the tanks, and they get air bound each time they are changed. Looking at their price (25 bucks) makes me think I should just buy a spare and keep it on hand. Doing fuel line purges with the hand pump is a PITA.

 

[Wxx3]

I have a similar installation on my vessel. An ordinary auto fuel pump (inline) which is keyed on when the ignition is on is the key when I do filter changes. Running it and purging all the air out is key. I have not determined if the pump was installed because of a low performing fuel pump, or the fact that the filters are above the level of the tanks, and they get air bound each time they are changed. Looking at their price (25 bucks) makes me think I should just buy a spare and keep it on hand. Doing fuel line purges with the hand pump is a PITA.

I plumbed in a low volume fuel pump, run with wireless relay. I use this to prime Racors when I change a filter. Works great.

But as I said before, I think Marty's issue is at the feed valve on the tank.