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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 06-28-2010
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Calling Yanmar gurus . . .

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.
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Last edited by Omatako; 06-28-2010 at 02:52 AM.
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Old 06-28-2010
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Unknown Oil Loss...

As the general location of the leak isn't identifiable at this time, the first and simplest thing I would do is to spin off the oil filter and make sure the o'ring hasn't blown out.
I hope the solution is something as simple as this.....Good luck....
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Old 06-28-2010
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Quote:
Originally Posted by TADRON View Post
As the general location of the leak isn't identifiable at this time, the first and simplest thing I would do is to spin off the oil filter and make sure the o'ring hasn't blown out.
I hope the solution is something as simple as this.....Good luck....
The above is probably the most common source of air leaks.

The second probable most common source is ALL the 'compression fittings' that connect all the tubing, etc. in the fuel delivery system. Compression fittings are essentially a ONE-TIME-TIGHTEN ONLY devices and easily suck air. The copper tubing end thats inside the compression fitting eventually 'relaxes' (strain relief) thus allowing aiar to be sucked in. Boat manufacturers use compression fittings because they are cheap and require no tools to assemble.
Better is double flared connections on stainless steel tubing.
To find air leak on a system with compression fittings - PRESSURIZE the system, then look for the leaker. Pressurization will also uncover a lift pump diaphragm that has developed a pin hole.

If you cant pressurize, then tighten each and every compression fitting with a 'fitting wrench' (wrench face comes in contact with 5 sides of the compression nut --- unlike a standard wrench which only comes in contact with 2 side of a nut.)
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Old 06-28-2010
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Two separate problems for sure.

First as described above is an air leak into the fuel system most likely between the bulb and the fuel pump.

The loss of all oil quickly could be a broken pressure pipe after the oil pump. I would follow the lines from the pump to the oil filter and in that area.

Gene
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Old 06-28-2010
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Perhaps the oil cooler or transmission cooler failed?
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Old 06-28-2010
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Just happen to be reading through a 4JH2E Yanmar Service Manual for another unrelated problem. I'd replicate your situation. Pour a litre or two of oil into the sump. Have some one else turn the engine over or start it up while you keep your eyes down near the bottom, so you can see which part of the engine the leak comes from. Don't forget to turn the engine off quickly though to avoid further damage. Once you see the oil spewing from a general location you can search more specifically for the source. I suspect that plug at the bottom of the dipstick tubing and also the oil pump which bolts onto the front of the block. Good Luck!
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Old 06-29-2010
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Quote:
Originally Posted by TADRON View Post
As the general location of the leak isn't identifiable at this time, the first and simplest thing I would do is to spin off the oil filter and make sure the o'ring hasn't blown out.
I hope the solution is something as simple as this.....Good luck....
Thanks for that - If the O-ring had blown out there would be oil all over that side of the engine, the oil filter area is clean and dry - the leak is not from there.
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Old 06-29-2010
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Quote:
Originally Posted by RichH View Post
The above is probably the most common source of air leaks.

The second probable most common source is ALL the 'compression fittings' that connect all the tubing, etc. in the fuel delivery system. Compression fittings are essentially a ONE-TIME-TIGHTEN ONLY devices and easily suck air. The copper tubing end thats inside the compression fitting eventually 'relaxes' (strain relief) thus allowing aiar to be sucked in. Boat manufacturers use compression fittings because they are cheap and require no tools to assemble.
Better is double flared connections on stainless steel tubing.
To find air leak on a system with compression fittings - PRESSURIZE the system, then look for the leaker. Pressurization will also uncover a lift pump diaphragm that has developed a pin hole.

If you cant pressurize, then tighten each and every compression fitting with a 'fitting wrench' (wrench face comes in contact with 5 sides of the compression nut --- unlike a standard wrench which only comes in contact with 2 side of a nut.)
Yep, I understand all of the above - like I said, I'm not concerned at this time about the loss of power - I personally think it's something inside the fuel filter (non return valve or something) because it has been happening since I changed the filter but it more like fuel flowing back to the tank than it is an air leak.

Anyway, my primary concern here is the oil leak.
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Old 06-29-2010
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Quote:
Originally Posted by Gene T View Post
Two separate problems for sure.

First as described above is an air leak into the fuel system most likely between the bulb and the fuel pump.

The loss of all oil quickly could be a broken pressure pipe after the oil pump. I would follow the lines from the pump to the oil filter and in that area.

Gene
The oil filter screws directly onto the engine block and I think the oil pump is internal. I can't see any pressure line externally but it had occurred to me that there may be something like that under the engine where I can't see or reach.

I'm hoping some Yanmar specialist will enlighten me.

Thanks for your input.
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Old 06-29-2010
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Perhaps the oil cooler or transmission cooler failed?
I can find a transmission cooler but not an engine one. If there is/was one that would be the most likely point of failure but I would have hoped it would be where it could be seen. Is it possible it may be under the engine? I sure hope so.
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