4JH2E excessive oil loss

I own a Yanmar 4 JH 2 E from 1998 with about 8,000 h on it. I didn't use the boat much in the last 2 years and especially the last half year it had perhaps 2 hours running time. It was always running really well with a little light grey smoke. A week ago I wanted to take her out, checked the oil level and realized that there was no oil left. I filled up, had the engine running and most of the oil disappeared again just going out of the bay and hoisting sails. There is a little bit of oil in the bilge but in my opinion never the amount I filled in. I had to move the boat to a different location yesterday and on a distance of 5 nm I had to stop half way after oil pressure went low to fill up again - so 2 times from empty to full, meaning close to 2 gallon of engine oil disappearing on a journey which normally takes a bit more than an hour. I noticed that the cooling water coming from the exhaust seems to be contaminated - there are some (oily?) streaks on the water when running the engine.
I'm at a total loss where all that oil is going and would be very happy if someone could point me in the right direction.

I'd start with the oil cooler given the data you offered...

makomark said:

I'd start with the oil cooler given the data you offered...

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Thank you very much for the reply.
If that is the cause, where does it leak to? - to the outside, so dripping into the bilge or to the cooling water going to the exhaust pipe?
I will go to the boat later, fill in some more oil and will try to reach that side of the engine while it's running without injury.
How could I determine if it's the oil cooler if it's leaking into the cooling water?
thanks again.

captainalf said:

If that is the cause, where does it leak to? - to the outside, so dripping into the bilge or to the cooling water going to the exhaust pipe?
...

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Yes, to the outside, usually the exhaust hose...

captainalf said:

How could I determine if it's the oil cooler if it's leaking into the cooling water?...
If it is bad enough, one can sometimes see the leaking in the exhaust discharge with the engine running. typically, it is best to remove the cooler and have it tested at a radiator shop. If they can locate a leak, they can usually repair it.

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Thanks so much for the input.
With 3600 gallon/h of water going through the cooling system I can imagine that the little bit of oil film I can see on a bucket of water I filled on the exhaust is all the oil going out. The bilge does not get a drop.
I'm now very keen on getting the oil cooler off and have it tested. Only problems are that on the tiny island I'm living on is no radiator shop and it's the transition time from SW to NE monsoon, which means that at any time the need can arise to move the boat.
However, as soon the weather looks stable enough I will get it out and to the mainland. I'll keep you posted about the developments.

i doubt the cooling water flow rate is anywhere near that value...but it is usually dependent on the engine RPM.

The radiator shop isn't a prerequisite but a suggestion. When we do similar tests, we typically pressurize an OIL path thru the cooler to 100 PSI, and then check the other paths for leaks (submersion of the whole cooler sometime helps, if done with some forethought).

Once the leak location is found, appropriate measures for repair can be made...worst case is the entire cooler needs replacement.