Yanmar 4JH-DTE Breather Tube Oil Leak

[Donahue]

I have a Yanmar 4JH-DTE that is leaking a pretty steady drip of oil at higher RPMs (above 2500) from the breather hose into the intake mesh/silencer. I think this is leading to some excess smoking (although not too bad). I know that some oil mist is supposed to escape and get sucked into the intake, but what I’m seeing is a lot more than a mist. I’m trying to figure out the cause.

There is virtually no blow-by pressure when I open the filler cap at high RPMs. There is a little steady putter when I open it at idle right after startup. There also doesn’t appear to be much oil mist flying around at high rpms either.

The breather cover, mesh, and shelter plate are completely clean.
The turbo is clean on the intake side and has light carbon film built up on the exhaust side. The turbo spins freely but is perhaps a little stiff. I’m going to pull of the turbo in the fall and have it rebuilt.

The exhaust elbow is bronze and has film of carbon similar to the exhaust side of the turbo, but is otherwise in good shape.

Beside the light smoking (blueish black) and the oil drip at high RPMs, the engine runs perfectly and can almost achieve max RPM WOT (about 3500-3600), pushing my 35500 lb boat to 8.5 knots in flat water.

The engine has either 1800 or 4800 hours. There are two hour meters; one at 1800 (currently working) and the other at about 3000. Boat was repowered in the 90s with the 4JH and there is not enough from the maintenance records to determine whether the old 3000 meter belonged to the old engine. I go with the higher number.

Any thoughts would be much appreciated. Is there a plugged oil port somewhere else in the lube system that could cause this? Oil can only get to the breather tube through the head cover and if there is little pressure or mist in there when I open the filler port, where is it coming from??? I thought that I overfilled the engine (filled to the top mark per the manual) so I removed about a pint. This may have improved the drip a bit, but it’s definitely still there. The oil level is now about the midpoint between the two dipstick marks. However, it’s hard to get a consistent read on these engines.

Thank you!

[ScottRhodes13]

It's just a guess, but you might try replacing the screen filter that is in the fitting where the breather attaches to the valve cover.

[Donahue]

That's a good thought, thanks! The baffle and other parts are clean but the mesh/baffle seemed a little compacted, maybe it's not separating the oil and air adequately anymore. New baffle and plate ordered.