Nuisance oil leak yanmar

Both of my motors, Yanmar 4HLA-STP, 240 Hp, 600 hours, have developed a small oil leak that is showing up in the same spot. I get maybe 1/4 to 1/2 ounce on the diaper just under the forward port corner of the oil pan after about 20 hours run time. No drip when the motors aren't running.

Not a huge deal, but I would like to eliminate it. Any idea of where to look for the cause?

Thanks.

I've been doing a little googling on this, and reading boatdiesel, it sounds as if I may be slightly overfilling my oil pan, especially since at fast cruise our boat runs at a fairly bow up angle.

I've always just filled to the top line on the stick, erring on the side of a little too much rather than a little too little (it's sometimes tough to get an exact reading). But they say better a quart low with these engines than a quart high.

Maybe I should run it a while just below the line, maybe 1/2 quart less, and see what happens?

I'm due for an oil change, and specs call for 2.6 gallons, I could put exactly that amount back in but I don't think that is all that accurate either as I don't think all of the old oil is completely extracted.

The manual for ours (4JH2-UTE) says to measure the dipstick 3 minutes after shutdown. There is also a mark scratched on the dipstick between the manufacturers high and low marks...presumably put there by the installer to account for the slope angle of the engine.

I'll look after work at my manuals. Pretty sure the operators manual is for the first time oil is added, and the service manual gives a different, lower amount.

It is common for the angle to require less oil to prevent whipping by the crank and subnerging some areas not intended to be submerged.


I always ran my cummins 2 qts low and oil use went way down.

The service manual had the amount (for our smaller engine) at 6.5 litres after reassembling the engine. The operation manual puts it somewhere between 2.5 litres and 7 litres.

Putting in a gallon plus a litre gives 4.8 litres, which is halfway between the minimum and max amounts and puts the oil level on the mark scratched into the dipstick...well...most of the time...because the dipstick shows a different level every time!

I can understand how the angle the engine is mounted at will create different results on dipsticks. For such an important thing, you would think they would make measuring the oil knuckle dragging simple and bang-on accurate every time. Having the dipstick curve into the oil at an angle seems like an afterthought.

It is very common to use oil running only because the pan is on the high side. Yanmars are notorious for needing to drain for up to 10 minutes before you get an accurate read.
We found on river tugs that by running our Detroit Diesel 12V's a gallon below the low line we saved over 75% of the oil usage. That would be over 60 gallons of oil a month per engine.
Better to run on the low side and change oil a little more often for peace of mind.

Most diesel engines I have run over my life have used more oil if the oil level was at the top mark. Each one seemed to have it's own spot for lower consumption. They always use more oil if overfilled. My Detroit mains will use a pint an hour at the top mark. When they get to a quart low they stop using oil.
Diesels with several thousand hours and some blowby will often have increased crankcase pressure and high oil levels only make the pressure higher. Sometimes blowing out seals. Especially old style rope rear main seals.