Yanmar 2GM20F-Oscilating RPM under load

[Alex Pascu]

IT happens when engine under load in gear, at around 2700 and up ,after 15-20 min. It goes down and up , but unless I lower the RPMthe situation worsen, sometines-not often- it shut off .No problem starting , anytime. It doesn't occur at lower RPM, about 2200-2500 even after an hour or so. I changed both fuel filters , but it didn't changed. I checked for air going in fuel supply , but it doesn't.The fuel is from trusty clean origin , allways checking it.No water in fuel . What can it be ? Anyone had similar occurance? The engine is on my 29.5 ,95' model' engine just 250 hours on it. will much appreciate some advise, Alex.

 

[Andy]

Yanmar highs & lows

Could the enjine be getting hot and smothering out? A cool running diesel is a happy diesel. Take away air, fuel, or cooling and the "iron mule" will get more and more stubborn. We rarely ever run over 2500RPM for extended periods of time. Try keeping the RPMs down at 2500 for a while and see if that helps. Your prop could be oversized (or barnacled up), or perhaps your stuffing box is too tight & not dripping water. As the shaft heats up from lack of water, it begins to seize and smother the lil mother?

 

[Bob E.]

check the governor

The governor is a complicated mechanism of levers, springs, and centrifugal weights that regulates engine speed by controlling the fuel input. It might have the effect you described if soemthing is wrong with it.

 

[Andy Falls]

Answer for Alex

I know someone who knows someone at Yanmar. His answer is...Andy it sounds like there is a fuel condition with this engine, Yanmarhas found that if the customer uses a Racor filter it is possible that thecustomer installed a 2 micron filter instead of a 30 micron filter. This is avery frequent mistake that is make.The condition could be a fuel starvation problem under load, or the governorspring is his problem. Both of these conditions will restrict the fuel supply to the engine and performace will be decreased.

 

[Raoul]

Varying RPM's

Alex:We recently ran into a similar problem with the 3GM30 on our Hunter 35. It took me a while to figure out that I had inadvertently put a kink in the fuel line, between the tank and the first filter), during some servicing. As soon as the engine was under load and consuming fuel, there just wasn't enough fuel to maintain normal RPM's. Good luck!

 

[Chuck Wolfe]

Just happened to me-fuel pump

Had the same symptoms last trip. Eventually I couldn't start the engine. It was the fuel pump.