Full Problem: Yanmar Diesel

[Rob19574]

Hi all -

I had a tough time starting my Yanmar - YSM12 (one-cylinder) diesel this season. I didn't change the fuel filters (I have a water separator and another filter on the engine itself) but thought I would get to it later this season. So last weekend it would not crank over (first time starting for the season). Turns out both fuel filters were bone dry - lost its prime. Odd as for the last 6 years she always cranks over on the first or second try. I filled the filter and bleed the system - started right up (I ran it for 10 minutes but did not leave the dock). This weekend at the dock I ran it again for about 10 minutes to test it: started right up but then after 10 minutes it stalled when I revved it up. Both fuel filters were bone dry. I bled the system and it started right up.

So I assume my filters need to be replaced which is fine and I plan on doing so next week. I am curious as to why the fuel system would run dry though. Could it be my fuel pump or does it sound like filters are clogged? I pulled the tank out of the boat 6 years ago - drained / cleaned it out and have never had a fuel issue since. Perhaps after 6 yrs I have water in there or something else going on. The injector is only 6 yrs old. I have not noticed any diesel leaks in the fuel system.

I am wondering why the system went dry over the winter - that has never happened before. I store the boat up north in NY. I did have the exhaust manifold off over the winter being repaired but that would not have caused this.

I appreciate anyone's thoughts on this and if I missed anything other than the filters just needing a change.

- Rob

 

[Stu Jackson]

No fuel

Rob, you've covered the two obvious things, but dirty fuel filters have nothing to do with no fuel.

Have you removed the screen in the intake fuel pickup in the tank?

I'm a dummy a lot, and once when I replaced the filters I forgot to turn the fuel tank shutoff valve back to open position. Imagine...:cussing:

 

[Joseph Shirley]

Could be that your vent is plugged pulling a vacuum on your fuel at the tank or your clogged filters create enough of an obstruction that you are pulling some air into the filter which would allow air to follow your fuel to the engine. You can check the first by just venting the tank, and the second by watching the filters as the engine runs.

Good luck

Joe S

 

[RichH]

Rob ... a possible reason for the 'missing fuel:
If you've not been noticing any fuel in the bilge, etc. and if you are 'handy' remove the 'lift pump'. Once removed put your fingers firmly over the inlet and outlet nozzle and by hand work the pump's lever, hold you fingers there for a long time and see if the vacuum (or pressure depending on which side of the check valve you are 'testing') that 'should' be generated, stays a vacuum (or pressure). If the pump slowly releases its vacuum (or pressure), then I would suspect that you have a pin-hole or small rupture of the pump's rubber diaphragm and the fuel is simply draining (over time) directly through the 'hole' and into the crankcase.

 

[Rob19574]

The vent line is clear - I checked that. Good point's Stu. Rich - that makes sense that something is wrong with the lift pump. I will need to do some more research on this one.

Thanks guys - Rob

 

[Jonny PIP]

HI Rob I have YM12 in my 30 hunter and anything can happen to that engines,they are old.

 

[DougM]

Look at your fuel lines. They may lok ok to just a casual glance, but the rubber my have some tiny little cracks. They won't necessarily leak fuel, but they will allow air to be sucked into the system. A friend chased a similar problem last season, changed filters, changed pumps, cleaned fuel tank, still had the problem. Pulled a fuel hose and had it lying on the counter, and when he picked it up there was apool of fuel around it. He bent the hose and discovered the cracks which were invisible in the normal hose position. He changed all the fuel lines and the problem disappeared.

 

[kloudie1]

Yup.. Ya have an air leak, probably BEFORE the first filter ... probably in one of the hose fitting connections or the hose itself.. but it could be in the filter gasket or filter housing gaskets..

 

[Rob19574]

So here is an update: My fuel gauge stopped working at "1/2 tank full". My wife and I have 2 small children under 4 and our long-cruises have been very limited. We basically motor 1 mile out - sail and motor one mile back. I thought it was odd that is has not moved but year-over-year I did not recall where we left off. My Yanmar uses very little fuel.

So I pulled the fuel-pickup to check for a clogged and realized I had less than an inch of fuel in the tank. I wet-store the boat on a creek all winter and over the winter there is on occasion some light rocking that must have broke the siphon in the tank and allowed air into the system. I changed all the filters as they needed replacing and all seems well (knock-on-wood). So I have clean filters and decided to pump out the remaining inch of fuel to just start fresh on everything. I do need to get a new tank gauge as well!

Thanks for the advice here.

- Rob

 

[Ross]

With the sending unit in hand and the power on, move the float back and forth while watching the gage. It may have been stuck. Or the gage may be stuck.

 

[Rob19574]

Yeah - I tried that and it works outside the tank but i think the gauge was made for a larger tank. My first couple of yrs with the boat I always topped off the tank in the beginning of the season and never realized 1/2 tank was approaching empty. Good thing i found out at the dock...

 

[kloudie1]

Yup.. air leak by intake in air space.. Good that ya found it, Rob.
Part B: some fuel tank senders had adjusting screws that let you set where it reads E and F .. Look at the parts just below the mounting flange and see if ya have some adjusters.. sometimes shortening the float arm will do it too. Good luck with the gauge..