High oil consumption and smokey exhaust.

[Contest1]

I rebuilt my old penta 2002 year before last.
I goes like clock work and starts after a couple of turns.
Didn't rebore the cylinders as the ring clearances seemed good.
Anyway was hoping it would improve when the new rings bedded in but no luck there.
The oil consumption is about half a litre an hour at 1700 revs.
I'm thinking of trying 5w 30 oil instead of the 10w 40.
Any opinions wekcome

 

[Old Harry]

I rebuilt my old penta 2002 year before last.
I goes like clock work and starts after a couple of turns.
Didn't rebore the cylinders as the ring clearances seemed good.
Anyway was hoping it would improve when the new rings bedded in but no luck there.
The oil consumption is about half a litre an hour at 1700 revs.
I'm thinking of trying 5w 30 oil instead of the 10w 40.
Any opinions wekcome

A thinner oils will be worse why not use 15/40

 

[neil_s]

If you're thinking that a thicker oil will reduce the oil consumption, then I would suggest you need 20W 50 not 5W 30. Maybe the oil is getting past the valve stems?
Maybe your engine is suffering from a blocked crankcase breather?

 

[Contest1]

A thinner oils will be worse why not use 15/40

Thanks. I must admit I got the idea for 5w 30 from an article I read online.
Obviously not the best source.

 

[Contest1]

If you're thinking that a thicker oil will reduce the oil consumption, then I would suggest you need 20W 50 not 5W 30. Maybe the oil is getting past the valve stems?
Maybe your engine is suffering from a blocked crankcase breather?

Replaced the valve stem seals and pushed a welding rod through the breather port in the head. Seemed to go right into the sump
Will try the 15w 40 first then maybe the 20w 50.

 

[grumpygit]

I rebuilt my old penta 2002 year before last.
I goes like clock work and starts after a couple of turns.
Didn't rebore the cylinders as the ring clearances seemed good.
Anyway was hoping it would improve when the new rings bedded in but no luck there.
The oil consumption is about half a litre an hour at 1700 revs.
I'm thinking of trying 5w 30 oil instead of the 10w 40.
Any opinions wekcome

Did you glaze bust or hone the bores before fitting the new rings?

 

[lw395]

Half a litre an hour of sump oil is a helluva lot.
It is seriously near running on burning the sump oil, which is a runaway condition which will rev your engine to destruction.

If the exhaust is really smokey, then perhaps the oil is going down the valve guide, not getting into the cylinder to fuel the engine.

One possible thing to look at is, is the top end flooding with oil?
If yo utake the rocker cover off immediately after running, is ther more oil than there should be?
Either a blocked drain to the sump, or the rocker feed pouring in too much?

If the engine is getting up to temperature, then to have a thicker oil at running temp, you want something like a 10w60, but leaving aside the debate about such synth oils, this would be papering over the cracks.
If the ring gaps were OK, I'd be thinking valve guides slack. Unless the rocker box is just filling with oil. I had this on a car once, a shot cam bearing.

 

[rotrax]

I had heavy oil consumption with a 3 cylinder Yanmar. It came filled with a 5/20 modern semi synthetic marine oil and with a spare 4 litre container of same.

It was all gone by the time we got to Gosport from Watchet, including buying more oil in Falmouth. Little wind, so the donk was on almost all the time.

Changing to old style 20/50 GTX cured the problem completly.

 

[KellysEye]

Heavy oil use indicates new piston rings are required, as I found.

 

[PeteCooper]

Heavy oil use indicates new piston rings are required, as I found.

It can indicate that - but it is by no means a given conclusion.

 

[colind3782]

If you honed the bores the new rings would need to be bedded in by running the engine at high power and temp for a while. If not, the bores get glazed and the oil consumption will be high. Only one of the possible reasons I'm afraid.

 

[Skylark]

Half a litre an hour suggests a pretty serious problem. I'd also be concerned about the risk of run-away.

The oil should be the type, spec and viscosity as recommended in the manual / by the manufacturer.

Assuming it wasn't drinking oil prior to the rebuild, everything changed or serviced falls under suspicion.

Oil appears to be entering the combustion chamber. At the quoted quantity, I doubt that blow-by is a culprit....but always worth making sure that any connecting lines and any non return valves are clear and functioning correctly.

Piston rings and bores need investigation, as do the valve guides and seals.

Not a nice problem to have but it needs sorting without delay. Good luck.

 

[Tomahawk]

What colour is the smoke?

If white, it would indicate oil getting into the exhaust and simply vaporising which would indicate leaking exhaust valve guides. Open the exhaust just before where it joins the sea water pipe.. If it is full of oil... you have found the culprit.. Also look at the exhaust water .. is it very oily leaving a pronounced smear on the water? .. again a symptom of unburned oil in the exhaust.

If black, it has to be getting into the cylinder and being burned.
The two options are inlet valve guides or rings.

Look at crankcase pressure... open the breather.. If you are getting a lot of gas.. (smoky?) it would indicate combustion pressure by passing the rings with the possibility of oil getting into the cylinders on the induction, exhaust strokes. But you say it starts well.. That indicates good compression which you would be losing if there was by pass in the rings.

Can you get hold of a compression tester? If so swap out one injector at a time and check compression. .. The bad news if it is rings... is for you to work out.

 

[oldharry]

Half litre an hour is too much for simple blow by. More likely a ring has failed some way - broken, glazed or whatever pressruising the sump, and blowing oil through the breather into the air intake. very dangerous, as it will eventually run away to destruction running on its own oil.

To check it. close off the breather, remove the oil filler cap and using a rag, block it off with your hand. Run the engine up for 10 - 15 seconds at around 1500 -2000 revs. If there's a whoosh as soon as you release it then there is a piston/ring fault, causing blow by. I had an old Perkins prima that did exactly the same due to worn bores. Ring gaps were around 25 thou, where they should have been max 12. That was all that was wrong but it used buckets of oil! I was able to run the breather via an oil tin to collect the oil and put it back in to the engine just to keep going the rest of the season. Saved a small fortune in fresh oil!

Yes I know, but it would be filtered by the engine before it got to any close tolerance parts, and the engine was going to have to be rebuilt anyway! The engine shop later reported the crank etc was fine.

 

[Contest1]

No. Too late now. Maybe I'll pull the engine apart again in next winter. A rebore seems to be the most likely answer. Im not a mechanic but as it starts handy and is a sail boat I might just try the suggestion of 20w50 oil.

 

[oldharry]

No. Too late now. Maybe I'll pull the engine apart again in next winter. A rebore seems to be the most likely answer.

You need to know whats wrong before running it for any length of time. Oil loss on that scale is potentially serious, and you could well end up with terminal damage if it throws a piston or worse. Could lose you the boat and your life too.... these things have a way of happening at the worst possible moment!

 

[Boathook]

Half litre an hour is too much for simple blow by. More likely a ring has failed some way - broken, glazed or whatever pressruising the sump, and blowing oil through the breather into the air intake. very dangerous, as it will eventually run away to destruction running on its own oil.
.

A work colleague had his company diesel car do this. Couldn't even stall it due to the high revs. Engine blew up causing damage to engine compartment and wrote the car off. At least he could walk away and watch from a distance.

 

[Contest1]

What colour is the smoke?

If white, it would indicate oil getting into the exhaust and simply vaporising which would indicate leaking exhaust valve guides. Open the exhaust just before where it joins the sea water pipe.. If it is full of oil... you have found the culprit.. Also look at the exhaust water .. is it very oily leaving a pronounced smear on the water? .. again a symptom of unburned oil in the exhaust.

If black, it has to be getting into the cylinder and being burned.
The two options are inlet valve guides or rings.

Look at crankcase pressure... open the breather.. If you are getting a lot of gas.. (smoky?) it would indicate combustion pressure by passing the rings with the possibility of oil getting into the cylinders on the induction, exhaust strokes. But you say it starts well.. That indicates good compression which you would be losing if there was by pass in the rings.

Can you get hold of a compression tester? If so swap out one injector at a time and check compression. .. The bad news if it is rings... is for you to work out.

Thanks. The exhaust is gray definitely not black. New rings and bearing on the rebuild and the ring gaps were spot on. I'm going to investigate your suggestion as I'm not convinced its poor compression. It's starts no problem.

 

[Contest1]

A work colleague had his company diesel car do this. Couldn't even stall it due to the high revs. Engine blew up causing damage to engine compartment and wrote the car off. At least he could walk away and watch from a distance.

Wow. I'm more concerned now. Going to get it sorted before I use it again.
The breather has been mentioned several times but I'm not aware there is one. There is a filler on the block above the oil pump. The rocket cover has no outlet. There ia pressure equalisation port through the block that's clear. Anything I'm missing?

 

[Contest1]

Further investigation has thrown up two issues.
I decided to check the reduction valve. I expected the spring chamber to be full of oil but it was dry. Gave the engine a few turns by hand a oil started coming through as you would expect.
After reassembly still smokey, gray white with no oil scum on the water. Small oil leak at the closure plate probably indicates its now operating operating correctly.
Took off the rocker cover to check clearances and noticed that the decompression bar does not depress the back exhaust valve. The tappet operates it OK but the when the decompression lever is moved away from the ground flat it dose not depress the valve. Very odd. The tappet clearence is OK at 30mm. Could this valve be failing to close fully.? Further investigation needed??