My engine is a Yanmar 4JH2E (I think) non turbo 4 cylinder I think 49hp, it has done abou 3900 hours.
I will try and put this into clear perspective and the first description of a problem is not the subject - be patient
this is a long post.
For a while now I have been having some issues with the engine losing power shortly after being started, sometimes it waits about 10 minutes before it manifests itself. The engine RPM falls off, stutters and won't rev up. I go down below and pump the fuel bulb in the line, the stutter clears and from then on it doesn't happen again until the boat has been left for a week or more. This has been happening for several months BUT like I said that is not my problem. I'm just setting the stage.
This weekend we were motoring out of our anchorage and the engine sounded sweet - the loss of power never happened on its normal schedule. Then, probably 45 minutes into the motoring session, the engine lost power.
At the same time there was a brief smell of hot oil. I checked the instruments and saw nothing unusual. The power loss lasted about 15 seconds and then cleared on it's own and the engine started running sweetly again, totally against the norm. I went down below to check the cause of the hot oil smell and saw nothing that scared me.
I went back on deck, couldn't have been away more than a minute and then the alarm buzzer went off. I checked the instruments and saw no oil pressure. I immediately killed the engine. There was no noise, no misfire, no abnormal activity of any sort. Even the hot oil smell was gone.
I went back down below and had another look and what I found beggars belief. The entire contents of the sump was lying in the bilge. Let me make that clear - ALL of the oil in the engine was now in the bilge.
I know this because I later scooped it all up and recovered just short of 6 litres.
But the uncanny part is that I can't find any source of a leak. And I mean nothing. I have checked all around the engine with a strong lamp and there is no sign of where the oil could have come from. The only part that I can't visually check without removing the engine is the actual bottom surface of the sump and the rear of the engine inside the bellhousing.
So two things spring to mind. Either a sump plug has fallen out or there is a hole in the sump. Firstly I don't think there is a second sump plug - the first one is the dipstick connection to the sump but that is secure and dry. And in any case, if there is another sump plug it has been secure for three years at least, why would it come loose now?
I can't see under but I ran my hand over as much of the sump as I could reach and could feel nothing like a hole or a crack. My hand came away with a smear of oil but it was light enough to be just a smear, no droplets. With no ominous noises I find it hard to believe that anything inside the engine would have impacted the sump. With the kill cable pulled the engine still cranks normally with nothing out of the ordinary.
I've thought about the rear main oil seal popping out but I can't believe that that would completely empty the sump in a few minutes. I have checke the workshop manual I have and there is no reference to any external oil pipes that may have fractured.
Obviously I have missed something because the above tale sounds and probably is highly implausable. I have wracked my brains and can't think of a logical scenario that would cause this. Any useful thoughts members may have on this would be of considerable value since hauling the engine out of my boat is a nightmare job and if I can avoid it I would really like to try.