Yanmar 3ym30

[Stolen Kiss]

engine starts perfectly when cold,however go for a sail for a couple of hours and it needs a serious amount of cranking to start. Have fitted a new filter. Repeat it starts and runs perfectly when cold.
thanks Peter

[Shoalcove]

Could be a restriction in the fuel system that forms a bit of a vacuum as the engine is run. When you go to restart it the engine is suffering from fuel starvation and needs a lot of cranking. If this is the case, after the engine sits for an extended period, the fuel seeps back in and the engine fires right up. I'll qualify my answer by stating up front that I'm not a mechanic but I have read of similar problems. My diesel education is limited to keeping a 30 year old clunker going for longer than it wanted and then replacing it with a new 3YM30 (which has worked perfectly).Good luck!

[Chief Engineer]

Sometimes, water flows in thru the exhaust line....the resulting full exhaust line and water lift muffler gets filled. The pressure of the engine cranking over is not enough to evacuate the water in the lines.

[Cheechako]

Originally Posted by Chief Engineer

Sometimes, water flows in thru the exhaust line....the resulting full exhaust line and water lift muffler gets filled. The pressure of the engine cranking over is not enough to evacuate the water in the lines.

yes, what he said! also, it could be getting just a little into the aft cylinder depending on your setup...

[Stolen Kiss]

Thanks all, but there is definatly no water getting in,it turns over too easily.

[Chief Engineer]

The water may not be getting to the engine....but if it fills up the exhaust system, the backpressure will not allow the engine to start.

[Stolen Kiss]

Exhaust is way above waterline and this problem is new

[Shoalcove]

Well, if Chief engineer is correct, you may want to check your anti-siphon valve in the cooling water line. The ones with a flapper (Vetus) can freeze closed with salt and no longer function properly. They can come apart and be rinsed off as regular maintenence. I'm a big believer with starting with the easy stuff!!
Also a gunked up screen on your fuel pickup in the tank can lead to the condition I mentioned earlier.

[DeepFrz]

If you have a screen on your pickup tube remove it for your own safety.

You don't mention how long the engine is usually run when you go for a sail. If you run the engine under load at the dock for an hour or so what happens (at about half throttle)? Does it keep right on ticking or does it stall out after some time? If it stalls out after a period of running then that lends credence to a restriction in the fuel line.

Any other information that you can give us would help us diagnose the problem.