Yanmar 3GM30 running well but using a lot of oil.

[NotEntirelySure]

I'm hoping someone might have some thoughts on my engine dilemma prior to me ripping the head off it to hopefully get a better idea of what gives.

40 hours of use after firing up this old Yanmar its aggressive oil consumption is starting to annoy and concern me.

It had sat, perhaps only operating for a few hours in 8 years prior to myself buying the boat (previous owner just lived in it).

I have used it regularly since (an average of 1.5 hrs engine hours per week).

It starts really well, has plenty of power (6.5 kts in 34ft Joubert mono hull yacht), hasn't missed a beat except it blows a bit of smoke and initially used about 45ml of oil per hour.

Now its closer to 75 - 80 ml per hour. It still runs extremely well though.

Other info -

This engine has been 'rebuilt' twice - firstly in 1998 by a firm I beleive to be very professional and a second time in 2010 by a firm perhaps less so.

The second rebuild is fully documented and included rings and big end bearings, a proper head refurbish (subbied out to pros) and the injectors were serviced/rebuilt.

My guess is it has done no more than 100 - 200 hours in the hands of the owner who had the work done in 2010 and as mentioned above only 40 odd hours since 2012.

Oil I'm running is Castrol RX Super 15/40.

Fuel consumption is between 1 to 1.7 litres per hour depending how hard I am flogging it.

I haven't driven it real hard as much of my motor to get out of the river is 4 kt speed limit and I was wondering whether the increased consumtion under my ownership is due to glazing up the bore a bit?

The harder you drive it, the more smoke there is which is pale blue.

The oil doesn't go black in a hurry at all either.

5 hours after a recent oil change and it still looks quite clear.

The oil that was it it when I bought the boat was black black though.

?????

Thoughts engine gurus?

Heavier oil and ignore it/hope that that slows consumption?

As I intend to go away in it in a few months for 2 months I keen to make sure its going to be reliable.

Many Thanks for reading, Andrew.

[Compass790]

Well it can be a number of things,
First thing I would do is download the manual from the CF library. That has troubleshooting tips that are good.
Sitting for a long time is bad for us & engines. You may simply have sticky rings BUT there are multiple possibilities.
I'd go for sticky rings for a start, you could have rusty bores from sitting for so long. I'd GUESS rusty bores is quite likely.
My tip is to do a compression check for a start.
I doubt the oil has anything to do with your problem.
Have never seen an oil problem do that. Except for no oil.
Some people recommend a full bore ( WOT) run to free rings. I'd try some kind of carbon cleaner first but others on the forum might be able to give better tips if they have had a liitle used engine. can't see any problem with a WOT trial tho.
Keep posting back how you go please.

[Compass790]

Must say your description is very good. Hard to diagnose problems without a good description. Yr pale blue smoke is oil but you knew that anyway frm the consumption.
I think I'd try some ATF down the bores for a start.
You don't say how yr mechanical skills are as that has a bearing on the possible solution.
My experience is that oil consumption is not necessarily related to reliabilty but it depends on what causes the high consumption.
I know a bloke that had a bulldozer which used about 10 litres of oil per day. He did that for years. His problem was a worn out engine but he knew it wasn't likely to be a catastrophic failure.
Anyway YMMV

[Wotname]

While Compass790 has given you a good response and it makes sense, I wonder if the engine was ever run in properly after the last rebuild (new rings etc). They have never seated and continued low power setting are glazing up the bores.

A badly glazed bore is often not recoverable but IMO, you might be lucky - it might not be too late!

I would try an Italian tune up - bring the engine up to temperature normally and then operate it at high power settings (including WOT) for five to ten hours. High power meaning above 3,000 rpm and up to 3,600 for a 3GM30. Maximum continuous is 3,400 with 3,600 OK for a two hour interval.

[sailah]

A compression AND a leak down test are fairly simple to perform before you go taking things apart and can help you zero in on the problem spot. Once you take things apart, it's up to you to spot the problem.

[skipperpete]

Is the engine showing signs of crankcase pressure? If you take the oil filler cap off while she’s running you can get a good idea if blow- by from worn rings is the problem. Could be valve stem seals but thats a long shot. Is it leaking any oil?

[moseriw]

Well I think you do know very well what the meaning of blue smoke is - OIL!!!
Oil that is burnt in the cylinders.


So ripe off the head and let it check by a professional
Clean the block very carefully andmount the head as per builders instruction.
Be very careful to follow the manual EXACTLY!!!v Which nut when and which force fixing it.

If the head is OK - then, a pity, your piston rings are the problem.
And now I would think about a real professional complete rebuilt
That includes ALL NEW BEARINGS AND GASKETS
and even smoothen the crank.

The result is in fact a newly built engine block.

[Gaia]

Might it be worthwhile to replace the seals on the valve lifters? You can do so yourself in place. Those seals harden and if they allow oil past you would see what you do.

I recently this this on my 3ym30 although that was part of a ring and valve job but I became convinced that it is easy to replace the seals without removing the head. You remove the rocker arm and valve springs with care. You just need to bring each cylinder up to the top so that the valves do not drop down. I bought a valve compressor from Autozone but in the end made my own out of a piece of Aluminum and used the rocket arm bolt holes to press the valves down. A magnetic pick up tool works well to grab the halves of the spring retainers.

It is a while ago that I did this but if you are interested give me a shout and I can give you a better description. On the other hand there may be others that might comment on the pros and cons of doing this before you throw the big dollars at the problem.

Good luck

Jim sv Gaia

You have nothing to lose as it is not expensive or time consuming to do this

[Cpt Mark]

As said above. Or just carry oil with you. Diesels are pretty robust. I was Captain on a tug and we used gallons per day. Commercial op and they're not taking the boat out of service until they had to.

[Gaia]

Originally Posted by Gaia

Might it be worthwhile to replace the seals on the valve lifters? You can do so yourself in place. Those seals harden and if they allow oil past you would see what you do.

I recently this this on my 3ym30 although that was part of a ring and valve job but I became convinced that it is easy to replace the seals without removing the head. You remove the rocker arm and valve springs with care. You just need to bring each cylinder up to the top so that the valves do not drop down. I bought a valve compressor from Autozone but in the end made my own out of a piece of Aluminum and used the rocket arm bolt holes to press the valves down. A magnetic pick up tool works well to grab the halves of the spring retainers.

It is a while ago that I did this but if you are interested give me a shout and I can give you a better description. On the other hand there may be others that might comment on the pros and cons of doing this before you throw the big dollars at the problem.

Good luck

Jim sv Gaia

You have nothing to lose as it is not expensive or time consuming to do this

I used incorrect terminology in the above. The seals that might be causing your excess oil consumption are properly called valve stem seals and the two half round gizmos that keep the spring under tension are called cotters in the 3ym30 manual. Valve caps, cotters and valve stem seals are all available from Yanmar and are not expensive. It will pay to examine the springs and valve guides while you are at it. Cleanliness is of course paramount.

Jim

[a64pilot]

Originally Posted by Wotname

While Compass790 has given you a good response and it makes sense, I wonder if the engine was ever run in properly after the last rebuild (new rings etc). They have never seated and continued low power setting are glazing up the bores.

A badly glazed bore is often not recoverable but IMO, you might be lucky - it might not be too late!

I would try an Italian tune up - bring the engine up to temperature normally and then operate it at high power settings (including WOT) for five to ten hours. High power meaning above 3,000 rpm and up to 3,600 for a 3GM30. Maximum continuous is 3,400 with 3,600 OK for a two hour interval.

This, run her hard, and long, but watch oil pressure. If pressure begins to drop a lot back off, you have bigger problems.
It is very likely that the rings were never fully seated, I doubt there has been much bore glazing, while bore glazing can happen it’s only very, very rarely ever from light loading and 4 kts cruise isn’t light loading, charging batteries at a high idle for hours day after day is and many do that and don’t glaze their bores.
Bore glazing can often occur from too high a cylinder wall temps, it cooks the film on, just like burning something in the oven will glaze the oven walls.

Anyway babying a newly overhauled engine can lead to the rings never properly seating and the engine will use oil it’s entire life and have excessive blow by, excessive blow by can overheat the oil and soot it up prematurely.
Very often running one hard until oil consumption stabilizes is the best you can do, next step is disassembly and rejoining the cylinder walls.

I was trying to link to a Lycoming service letter, but it seems Lycoming has been hacked by a Chinese company selling furniture?

[Scubaseas]

You might try Rislone Engine Treatment or even Marvel Mystery oil if available in Oz but from your description it sounds like glazed bores. Try freeing up the rings with either of the above. I would not go heavier on the oil. Synthetic oil may last longer though

[a64pilot]

The reason why running a motor hard seats the rings is that the more power an engine makes, the higher the pressures in its cylinders are. Rings are made so that pressure forces them against the cylinder walls to prevent blow by, so the higher the pressure, the more force the rings exert against the cylinder and the more likely that they will wear into each other.
It’s usually Iron I’m steel, so there is nothing soft to easily wear in.
It’s also one reason why running an engine hard most of the time accelerates the wear and cuts into its life limit.
Don’t baby an engine until after it’s been well broken if.
Modern machine production tools have gotten so good that an almost perfect fit now exists on new motors even before one is started, so there is very little if any break in now on modern new motors.
However ones that have been overhauled may not have been done so with the precision of modern manufacturing, and for those maybe we need to go back to the old way and break them in, especially if a “dingleberry” hone was used, they are completely non precision things, no control at all.

The controversy is of course don’t run one hard until the bearings etc have well worn in, they may be tight and running hard right away may be bad.
Bearings are soft and will polish in in a few minutes so on the very first run, run it at a high idle to ensure good oil pressure and to break in the camshaft and don’t put it under a high load and run it for 15 min or so.
Then you can proceed to breaking in the rings.

If anyone is interested, the camshaft and lifters are the most highly stressed parts of any four stroke engine, they are steel on steel, bearing material wouldn’t survive.

[a64pilot]

Originally Posted by Cpt Mark

As said above. Or just carry oil with you. Diesels are pretty robust. I was Captain on a tug and we used gallons per day. Commercial op and they're not taking the boat out of service until they had to.

So long as there is good oil pressure and it cranks easily and makes good power, oil consumption isn’t a really a problem, just keep it topped off.
In fact back about WWII time the Brits did a paper on wear vs oil consumption, it seems that light oil consumption really reduces ring and cylinder wear, which makes sense as if there is no consumption, then the rings aren’t as well lubricated.
1030’s to 1940’s the Brits were probably ahead of the rest of the world with piston engines.

[Cheechako]

Originally Posted by skipperpete

Is the engine showing signs of crankcase pressure? If you take the oil filler cap off while she’s running you can get a good idea if blow- by from worn rings is the problem. Could be valve stem seals but thats a long shot. Is it leaking any oil?

I'm with skipperpete. Crankcase pressure evident when you remove the oil fill cap?
The 3GM have a history of cracked pistons , often the lowest ring and/or skirt. They may run fine or may be hard starting. With two rebuilds though, one wonders if that would be it already. Mine did so at 2000+ hours.
But if you have blowby out the filler cap when open, it's rings or pistons.
Valve seals will give you smoke at first start, but not big oils consumption.