Yanmar diesel engine cutting out

[svrevelations]

During the past 6 months or so, on just about every trip we do the port engine will cut out after awhile. The diesel motor starts properly and runs for about 20 minutes or so. Then it will first start dropping revs and go back to normal revolutions. For about 20 minutes, under power it will rev at 2800 rpm and then the rpm will drop to something like 2000 for a couple of seconds and then back up to 2800 rpm. This up down rpm's will continue for about 5 minutes and the engine then finally cuts out. One is able to immediately restart the engine but it will behave in the same manner.

We have Racor fuel filters and Algae X ( Algae-X - In-Line Fuel Conditioners ) inline fuel conditioners. The Algae X people came around to the yacht and claim that there is water suspended in the diesel fuel. They suggested that they bring a mobile machine to the yacht which will filter out and clean up the fuel in our diesel tanks.

My problem is that this will only address the existing fuel in the tanks and it will not sort out future water problems. I am indecisive and not sure what to do next. I need to find an effective, yet permanent solution for this.

Your suggestions will be appreciated.

[Jesse]

A water/fuel separator should accomplish what you are looking for. Matching the filter with the fuel flow demand of your engines is important and should be easy with the large selection available.

[Cheechako]

sounds like it's starving for fuel or getting air in.
a) Check your racor and look to see if the fuel is up to the top when you remove the top. If not .. it's starving.
b)Another problem might be the engine filter... has someone put a low micron filter there? (2 micron? maybe even 5 micron) or is it old and got algae in it? I've removed tehm from a running engine and the whole thing was clogged with rubbery almost latex like algae!
c) your pickup tube could be getting blocked inside the tank.

[d design]

You have air in the system. Check your owners manual for proper bleeding procedure. What model is your engine?

[SailPenelope]

Take care of everything mentioned above. We even purchased a "Filter Boss" which gives you good feedback......you can also make the equivalent yourself, if you're handy.

Unfortunately, our problem turned out to be rust from the fuel tanks......very, very fine rust. Passed through all the filters, even 2 micron, and messed up the fuel injection pump. Same symptoms as yours, except in addition, finally, gradually slowing rpms until it never ran again.

New fuel tanks and new fuel injection pump. What's money for?

[svrevelations]

Originally Posted by d design

You have air in the system. Check your owners manual for proper bleeding procedure. What model is your engine?

Not exactly sure right now as I am not on the boat at present.
It is a 40 HP 3 cylinder engine about 2006 model with 250 hours.

[svrevelations]

Thank you for the response!
It certainly seems like we need to do more investigation to find the problem.

[marlinmike]

Take a look at the fill cap area and make sure the O ring is in good order, if missing or cracked then that's were the water is coming in. I too would recommend having a company come in a "polish/filter" the current fuel in the take. Replace both filters as well. Not sure when they were changed last, but once a season is a good thing.