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

[kmacdonald]

You say it starts really well. Does that mean less than a second or almost instantly? If it does either the compression is good. My best guess is valve stem seals. Did the second rebuild document their replacement? They are simple and inexpensive to replace on most engines.

Tie it to the dock and do a bollard pull. Run it in gear at 80% max rpm for a few hours and recheck oil consumption.

[Scaramanga F25]

A guess: a broken oil control ring(s)

[kmacdonald]

Originally Posted by Scaramanga F25

A guess: a broken oil control ring(s)

Very possible. If the rings aren't gapped properly they can break right away, sometimes catastrophically.
Bad valve seals usually present as a lot of smoke at startup with diminishing smoke. Depending how bad the valve stems and guides are worn will determine the oil burn if the valve seals are bad or even missing. If it sat for a long time without running the valve seal can stick to the valve stem and be pulled off the valve guide when started. This would account for large oil consumption.

[kmacdonald]

A top end gasket set usually includes the head gasket, valve cover gasket, thermostat gasket, and valve seals. The set is cheaper than the individual parts.

[NotEntirelySure]

Thanks everyone for their advice. It is very much appreciated. As much as I know about pressurised crank cases and faulty rings I havent actually tried running it with the oil cap off that I can remember. Maybe I did that back at the start and it was ok.

I will check that again though.

I'll also fit an oil pressure gauge and go give it a hard time some more and log oil consumption to see if there is an improvement.

Starting wise it jumps into life immediately hot or cold.

Back with an update later today maybe.

Thanks again to everybody.

[Wotname]

BTW, is it a 3GM30 or a 3GM30F?

While the answer won't affect oil consumption, a 3GM30F will run hotter than a 3GM30. Neither should ever overheat when running at WOT but keep an eye on the temps if running hard for long periods. Oil temp can be checked easily using an IR thermometer shoot on the oil filter.

[kmacdonald]

That's good it starts right up. If it's not leaking somewhere it's the valve seals or oil ring. Valve seals are easy and you won't have to remove the engine. If it's an oil ring you have to remove the engine and oil pan to remove the big end bearing and pull the piston out the top. It's also an easy job but time consuming removing the engine. More than likely you can remove the head in place and check the valve seals. You could even see them with just the valve cover off. Look inside the valve springs. I don't know what your budget is but doing it yourself is fairly simple and not much harder than an oil change. Don't let it intimidate you if you're on a budget. My guess is the valve seals weren't put on it the last rebuild and that would be good news.

[Compass790]

Originally Posted by Cheechako

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.

Only thing is when you have lots of blowby normally the oil turns black real quick & OP says it doesn't but yes needs to be checked.

Agree his oil consumption sounds too high for it to be v/v guides.

Another thing he could try is removing the injectors & seeing if one is a bit carboned up showing the sick cylinder if one or more of his oil control rings is knackered.

Hope OP posts back what he finds

[skipperpete]

A diesel likes its oil like a sailor likes his rum.
Captain Ron to swab.

[NotEntirelySure]

Went down to the boat and played with a couple of things today.

There is nil blow by/crank case pressurization.

You can put your palm over the filler hole etc and there just isn't any pressure/fumes.

I checked the oil level carefully now that all the oil has drained back into the sump since the last time I used it. I worked out it used 50 - 60 ml last trip per hour. Most of which I was driving it quite hard. I thin that is a bit of an improvement.

On that basis I'm going to give it a few hours more hard driving and see what the consumption does I think.

It does blow a little more smoke at start up and then it settles down after 30 seconds. So I guess the guides or seals aint perfect.

Fuel consumption also on that last 1.6 hours use was fine at 1.8 litres per hour. Again while driving it quite hard (6.5 knots for extended periods).

Ran out of time to get started on the oil pressure gauge fitment, from memory though the thread in the block is 1/4 BSP or is in NPT?

On another instrument note I thought I would sort the non functioning tacho while I was there and traced it back to the instrument itself. Upon pulling it out of the panel it is super rusty around the joint between the glass and the case so I'm guessing moisture has been getting there and has wrecked something.

I will pull the rocker cover off at some point too as the idea of the seals getting pulled up the valve stems after a long time of not being run makes a fair bit of sense.

I'll order a gasket first just in case.

Thanks again everybody.

[NotEntirelySure]

Oh and does anybody know whether that tacho glass pops off or unscrews. Can't tell at the moment with the rust etc.

[Wotname]

The thread is BSP.

[Wotname]

No intention to insult your intelligence but are you aware of the difficulties of accurately reading the dipstick on these Yanmar engines.

I have found the best way to run the engine, shut it down, wait ten minutes, remove the oil filler cap, remove and clean dipstick, refit dipstick and withdraw immediately to read oil level. This seems to give consistent readings but others may have their own special procedure.

[Wotname]

Originally Posted by NotEntirelySure

.....
There is nil blow by/crank case pressurization.

You can put your palm over the filler hole etc and there just isn't any pressure/fumes.
.........

Did you remove the PCV tube (from the rocker cover to the air intake) and close off the exit point on the rocker cover before checking with your palm?

If not, you should otherwise it isn't a good check as the rocker cover is still open to the air intake manifold.

[NotEntirelySure]

Originally Posted by Wotname

Did you remove the PCV tube (from the rocker cover to the air intake) and close off the exit point on the rocker cover before checking with your palm?

If not, you should otherwise it isn't a good check as the rocker cover is still open to the air intake manifold.

Good point! Will test again soon.

Yeah the dipstick is a tricky beast.

I have been tracking the oil consumption over quite long periods though and then topping up with an accurate jug so I know exactly how much oil is going in and exactly how many hours so in the longer term I have accurate readings.