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

[a64pilot]

Driving in screws with a hammer works too.

If you have ever used a “real” hone, one that the stones are mechanically held in place so that when you insert it and tighten the wheel to expand it, you would understand, even a freshly bored bore off a a good boring machine, the hone when being turned you will feel tight spots initially, and maybe as you bring it up and down it will be tighter in one end of the bore than the other, this is small imperfections in the bore, that the hone will remove because of course it will wear off the tight spots faster, with an inside Mike you can get a bore to within half a thousands easily. Ideally you bore slightly undersized and take it to the perfect dimension with the hone as the hone is very precise.
A dingle berry hone will scratch grooves in the wall wherever the balls ride and there is no control of them at all, so you end up with microscopic ripples up and down the bore.
A hone with proper stones but that uses a spring has no control over the springs, instead of correcting any out of round conditions you may be making it worse.
Supposedly a dingle berry hone is good for knocking the edges off of the ports of a two stroke that theoretically could catch the rings, I’ve never had that happen, but I guess they have that one use.

[kmacdonald]

Ball hones come in different grits. If you are getting scratches you need a finer hone. They leave nearly perfect crosshatching. If you measured the bore of engines with 3 or 4k hours you will see they are no longer exact but are still fine for our sailboat engine purposes. There are tolerances listed in the specs of the engine and they will still be well within spec. They just need deglazed and crosshatching and a new set of rings. We're not building NASCAR grade engines and not paying NASCAR engine prices. If you want to bump it up a notch you can replace the cylinder sleeves or rebore and get new pistons and you will get more life out of the rebuild but it will triple the cost, at least.

[NorthCoastJoe]

I have a Yanmar 3GM30F. Never had a smoke or oil consumption problem at 40 hours down only 8 ounces of oil when I change the oil. I always run mine WOT every time I go out for a few minutes, do a few holeshots too. I get cruising speed at 2600 and have run at that rpm for over 11 hours nonstop with a few blasts of WOT mixed in.

I would try a few several hours runs. Give it a good workout and mix in some WOT under full load. If that does not solve your problem I would look at stem seals first that's easy then the rings.

[skipperpete]

I was going to disagree with the valve stem oil loss theory largely because on a 3GM there is no negative intake manifold pressure unlike a petrol engine but I happened to have a 2gm head out for inspection and I noticed how short the valve guides are so it might be possible to lose oil there.
The stem seals are damned tight on the valve guides though so its hard to see em coming loose and sitting high on the valve stem.

[dmcampbell]

Likely Valve Stem Seals

[Kolchac]

If I were you, I would follow Wotname's advice. Blue smoke is an indication of oil burning. Also, it could be a fuel droplet (injectors).
If you run diesel with a load of less than 70%, you can shorten its life.

[Lowesmarine]

Hi, the earlier Yanmar engines do not like the modern multigrade engine oils e.i 15W-40, they like a monograde oil either SAE-30 or SAE-40. Some Yanmar engines will use oil and smoke which are your symptoms. If the engine is a good cold starter, this is the best indication of the internal condition being good, then compression will be close to normal (Yanmar do not list a compression PSI in their spec data). Depending on your location, warmer climate try a 40 grade oil, colder use a 30 grade oil. This should stop the smoking and oil usage.
Good luck, Ex Yanmar Dealer

[thomhofmans]

I have changed my oil to mobil1 5-50 also try running the motor at top revs for half an hour under load every time you take it out this really clears the top of the bore and is good for engine we have same engine

[piloto]

Originally Posted by 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.

Ok, at the risk of sounding not too clinical, before you tear everything apart, pour some Marvel Mystery Into the oil or fuel, or both. I’ve used it in my plane and it frees up carbon deposits, which can lead to sticky valves or stuck rings. Worth a try.

[NotEntirelySure]

Thanks again everybody for more ideas.

I have gotten out a couple of times since the original posting and have driven it harder than I normally do.

Oil usage has dropped off a bit. Will continue to use it harder rather than lighter and will try to find a 30 or 40w oil and give that a go as suggested by Lowesmarine.

I'm interested to see whether it makes a difference.

Sounds like it will.

It continues to start fine and perform well accept for the oil usage issue.

I'll report back on the results of my various experiments.

[thomhofmans]

Just another note most people don’t use the engine ET bough under load diesels hate just idling or not being under load take my advice run it hard as according to the manual after normal running and before turning it off

[keith001]

Lots of good ideas. I had a high oil use once (airplane) that I finally tracked to the pistons being installed wrong. There is a front to each piston and it is critical that they be installed in the proper orientation. The pistons were marked. Just a thought.

[Ballsnall]

Definitely sounds like your valve stem seals have gone hard and allowing oil into the cylinder. Bit tricky to change in situ but quite doable. As has been recommended, do a compression test first just to be sure, but if you had blowby then you would have dirty oil at low hours which you say you don't. $50 for new valve seals and you should be good.

[Wotname]

Originally Posted by NotEntirelySure

.....
Oil usage has dropped off a bit. Will continue to use it harder rather than lighter and will try to find a 30 or 40w oil and give that a go as suggested by Lowesmarine.
............

Yanmar calls for CD oil rating and in Australia, Gulf Western Oil sells a SAE 30 single weight CD oil. Unfortunately the minimum size is 20L. Monoil 30 - SAE 30 - Gulf Western Oil - Gulf Western Oil

Small engine shops (mowers etc) often sell a Briggs and Stratton branded oil which is also a SAE30 single weight CD oil. These are available in 4 or 5 L containers.

[a64pilot]

A straight 30 W will be fine, be careful with higher viscosity oils though, many run them in older motors to get better oil pressure, and as their clearances have opened up enough to drop oil pressure in the recommended oil viscosity, they are fine doing so.

Because it’s higher viscosity it can also help reduce consumption.

However just as with everything else there are drawbacks, the drawback is that thicker oil will reduce flow, thats how it raises pressure, but reduced flow reduces cooling and lubrication.

For some reasons people get upset and want to argue with me when I tell then that piston engines are oil cooled, they say no they are not, they are water cooled cause that’s what they have been told. The cylinder heads and to some extent the cylinder themselves are water cooled, but every other moving part it’s the oil that does the cooling, camshaft, crankshaft and all the bearings heat is carried away by the oil.
Reduce the oil flow and you reduce the cooling.
In warmer weather you will be fine with 40W, just don’t be tempted to think a little is good, more must be better and start running even thicker oil.

I don’t think it’s your valve stems myself. Valve stems seals getting hard and wearing results in very little oil consumption, the biggest indicator of valve stem seal wear is it will smoke like a train when first started, then the smoke begins to dissipate as its burned off. Worn valve stem seals will allow oil to leak into the cylinder, that’s why one with bad seals will smoke so bad at start up, but as it’s a tiny leak it stops smoking soon after.

If running her hard for a period has much if any effect, it’s rings not seated well, and hopefully the running hard will seat them. If it has no effect, it’s not rings. I have never seen a bore so glazed that running hard had no effect, I have seen a few that it helped but the only fix was to hone the cylinders. A polished bore running hard won’t have much effect, the only fix is a hone.

Both glazing and polishing can be seen with a bore scope though if it’s a DI motor and you can get into the cylinder, if it’s an IDI I don’t think you can.

Excessive blow caused by polishing or glazing is bad because it increases ring and cylinder wear, soots up the oil bad, and cause excessive oil temps.