Yanmar 3GM30 oily exhaust exit

[Elliott1050CM]

Hi, hoping I can some some advice.

I have a Yanmar 3GM30 raw water cooled engine in Mt Elliott 1050 sailboat and a year ago after the boat went back in the water after a bottom birthday. As the bottom was clean and the prop and saildrive had fresh Propspeed on it I took the revs up to 2500 RPM, usual cruising speed is 2200 RPM and when I got back to the marina there was a black oily slick around the exhaust exit. This was the first time that this had happened and from that day on it has continued after motoring for 30 minutes or more at our cruising RPM. So not exactly sure what has happened.
The engine has done 3100 hours but with regular oil and fuel filter changes. I changed the exhaust mixing elbow 11 months ago as there was a small leak. I have taken the exhaust manifold off for a look and the front 2 exhaust ports had more soot build up than the rear one, it was not hard but more like a toffe, the exhaust elbow had the same gummy build up in it also, I cleaned this all out but the problem is still there.
No smoke is evident when motoring at cruising speed, but if I increase the RPM to 2800 for a short time then blue smoke comes out for about 30 seconds then goes away.
I’ve replaced the injectors, the engine was hard to start in the winter but never in the summer, with the new injectors it’s starting ok in the winter now.
Sorry, long winded story but if any one has any ideas what could be the problem that would be great and help me to know what I’m in for.

[Compass790]

The 3gm30's are known to have piston issues. The bottom ring land breaks. This is just hearsay from me but sailorchick & cheechako have personal experience with this so maybe they can chime in to comment if the piston problem matches your symptoms. See if the oily slick is diesel or engine oil for a start. Be good to do a compression test too.

[Lepke]

You probably have oil getting by the rings. Hard starting in cold weather, blue smoke, oily exhaust are all an a indicator of oil getting past the rings. If you use ether, too much can crack the rings.

[a64pilot]

I think what you have is normal wear, and at least some of it may be fuel.
I burn less than a half a quart per 100 hours, and my engine (4JHE) except for the hard starting acts exactly like yours.
A compression test and or a leak down test will tell a lot, tell you if you have a serious problem or not, or just keep taking care of it until one day it will have slowly gotten worse to the point you decide you need to do something.
I’d suspect unless broken piston, that day is years from now, and a broken piston I believe exhibits symptoms much worse than you have.
Should be smoky, excessive oil consumption, lumpy idle and not able to make full RPM, and hard starting, even in Summer maybe.

These are old style Diesels, and burning a little oil is a normal condition, just showing her age a little.

[Cheechako]

It's not gaining oil level on the dipstick is it?