Yanmar 3qm30f started leaking oil from multiple places.

[Nth]

I have an old 3qm30f that still starts and runs well but has suddenly (within a week) developed a large oil leak from multiple places. Looks to be coming from around the fuel pump, maybe front cover and the valve cover gasket. Definitely one spot on the lower front and one up the upper mid to back side.

My first thought is excessive crank pressure but before I tear into it wanted to get opinions and advice. Can I even get gaskets, rings, bearings and (I believe) sleeves for this engine? Only other complaint is it idles great and will run smooth at high rpm but runs rough in between. It's been that way since I've owned it so probably unrelated.

Thanks!

[AA3JY]

Blown head gasket? What does the color of your sump oil look..? Notice any coolent loss/ gain??

[S/V Adeline]

If equipped with a vent hose from valve cover to breather, make sure that is not obstructed.

[Nth]

Originally Posted by AA3JY

Blown head gasket? What does the color of your sump oil look..? Notice any coolent loss/ gain??

Oil is black and clean. Just did a filter and change 4 months ago. No coolant loses I've noticed. She doesn't even noticeable smoke. It'd be great if I get off with just a head gasket. I'm thinking maybe a broken ring.

Originally Posted by S/V Adeline

If equipped with a vent hose from valve cover to breather, make sure that is not obstructed.

I looked for one. Even checked the manual. Can't find any obvious breathers. I did find where some internal zincs are hiding behind a plate in the back of the head.

[Wotname]

Originally Posted by Nth

.......
I looked for one. Even checked the manual. Can't find any obvious breathers. I did find where some internal zincs are hiding behind a plate in the back of the head.

The breather on my 2QM20 goes from near the injection pump on the exhaust side to the bottom of the intake manifold on the other side. The manual suggests the 3QM30 is the same.

[lockie]

Might not apply to 3GM's, but 2GM's have a small oil line that runs from near the starter around to the rear of the block and is well known for rusting through and leaking (mine did). Worth a look.

[Wotname]

The QM series do have some pressurised external oil lines. Mine are flexible hose but you may have steel lines. Both can fail/leak.

[Compass790]

Without knowing your particular engine it's not uncommon to find engines that run rough at different rpms. It has to do with harmonics apparently
As for parts don't know where in the world you are but if in USA try toad marine. You should be able to get them is my guess but a much cheaper way to buy parts is try to find out the tractor engine that it is based on & then try Hoyes tractor.
With a sudden onset of multiple oil leaks it is likely to be blown head gasket or rings broken if breather is not blocked. i.e. as you guessed too high crankcase pressure
Hopefully someone who has rebuilt theirs will chime in to help you out with tractor equivalent.

[a64pilot]

If it starts well and makes good power, it’s not likely rings, usually worn or even moreso a broken ring causes low compression and a motor that’s hard to start.
Very often in engines there is an oil / mist separator in the valve cover that can clog, it’s sometimes just screen wire / mesh. It’s what the breather hose connects to.
When you change the valve cover gasket, be sure to wash this clean with mineral spirits.

[Compass790]

Originally Posted by a64pilot

If it starts well and makes good power, it’s not likely rings, usually worn or even moreso a broken ring causes low compression and a motor that’s hard to start.
Very often in engines there is an oil / mist separator in the valve cover that can clog, it’s sometimes just screen wire / mesh. It’s what the breather hose connects to.
When you change the valve cover gasket, be sure to wash this clean with mineral spirits.

Well I hope OP posts back what it is. I did say IF it isn't breather then it will be rings or head gasket. Definitely breather is first thing to check. Many multi cylinder engines will start ok with one sick cylinder ring problem. but we will see. It's just an opinion, hard to diagnose the problem if you are not in listening range.

[Wotname]

FWIW, the crankcase breather on this engine (3QM30) is a fairly long flexible hose (18" ~ 24") with an ID of ~ 1/4" (6mm). The nipples at end have an ID of ~ 4mm.

I guess this could clog up after enough hours.

I would be having a close look at the external oil lines first.

[jimbunyard]

Run it without the oil fill cap, if it seems there is too much vapor/pressure there, then there probably is (shouldn't be much).

That the engine runs good otherwise (starts fast, idles smoothly, achieves max rpm linearly, doesn't smoke or overheat, right?) points against major problems, though if there are, parts seem readily available.

[Cadence]

Originally Posted by S/V Adeline

If equipped with a vent hose from valve cover to breather, make sure that is not obstructed.

Ditto! You may only have a crank case breathing problem.

[Nth]

I started it up and removed the oil fill plug as jimbunyard suggested. There was some pressure but nothing more than a psi. Pulled the valve cover and didn't find any obvious signs where the gasket failed. It actually looked really health but I'll still order up a new one. I did notice oil around one of the decompression levelers. Maybe one of those seals gave out. Cleaned it all and put it back together.

I also found the breather thanks to Wotname. I never would have guessed the 1/4 hose coming from the injection pump area was a breather. I took it off the intake side, blew into it and felt a little give before it flowed clear. Not sure if it was a clog, oil or what. I'll pull the cover it comes out of next time.

As for the lower leak I pulled the fuel pump off as that's the highest part I could find oil on and its general crustyness. I'll throw a new diaphragm in it, cut out a gasket and screw it back on next whenever I find parts.

When it runs I can pull the decompression levers one by one and tell that each cylinder is firing. Still haven't found a smoking gun. I guess my plan is to degrease the whole engine, put a new valve cover gasket and fuel pump gasket on it then run it for an hour and localize the leaks better.

I did look at the external steel oil line that runs around the back of the engine and down by the starter. For where my leaks are that pipe is solid so don't think it's my problem. Will keep it in mind.

Thanks!

[Wotname]

Thanks for the update!

I will be surprised if you can find a fuel pump diaphragm. If you do, please post the source as I have never been able to get one but would very much like to!