2GM20 Blows Out Oil

[Sonosailor]

Hi Guys: I’m at my witts’ end.

1996 2GM20F: Please give me all the reasons this particular engine could throw out the dipstick and then spray the engine room with all the oil. I’ll respond with my knowledge and efforts.

Understand that less than 50 hours of run time ago, I ran the engine with mineral spirits instead of oil, to clean out carbon deposits, after it pushed the stick out a couple of times, and was being suspected of clogging the oil pressure sender. Each time this happens, I check the crankcase blow-by apparatus which, as you know, is terribly simple on the 2GM20.

[skybolter]

The first thing that comes to mind is possible damage to the piston rings. Running with mineral spirits could easily cause damage which would result in scored cylinder walls. This would cause blow-by which would increase crankcase pressure which would cause what you are seeing. A compression test could be useful for diagnostics. Also, this engine is prone to exhaust elbow carbon clogging. I suppose a partially clogged elbow could elevate the backpressure and cause the condition you are describing...just a guess, though.

[a64pilot]

You have to have a clogged or partially clogged crankcase vent, even with broken rings it should vent the crankcase well enough so that the pressure doesn’t build, will blow a lot of smoky air out though, I mean a LOT.
If it’s cranking easily, it’s not likely that it has excessive blow by or broken rings, that usually means low compression and a hard to start engine, if it’s hard to start, then you may well have a compression problem.

[cal40john]

Did you put the mineral spirits in the crankcase or the fuel?
With the engine running is there lots of flow out of the blow by tube?
Also try to open as close to the block if no flow.

Probably unlikely this is blocked, but its an easy check.

(Edit: I see A64 has the same idea)

[gonesail]

sounds like it's time to bring in a yanmar mechanic

[jimbunyard]

Run it without the oil filler cap. If the problem goes away, you have a crankcase vent problem; the vent system needs to be checked from where the gases leave the crankcase (i.e. the pressure side of any screen or baffle that may be present) to where they enter either the atmosphere or induction system.

[01kiwijohn]

Originally Posted by Sonosailor

Hi Guys: I’m at my witts’ end.

1996 2GM20F: Please give me all the reasons this particular engine could throw out the dipstick and then spray the engine room with all the oil. I’ll respond with my knowledge and efforts.

With that much blow-by, I'd have to suspect the rings/ pistons/ cylinder bores; assuming you've checked the external items pointed out by others.
Does the air intake screen have a lot of oil in there too? If so, you're in danger of having a "runaway".

[Boatwright]

Could be sludge loosened by the paint thinner is clogging your crankcase vent. The suggestion on removing the oil filler cap as a test may work, but it might be better to take off the valve cover before you run the engine again to clean up any sludge that may be blocking things up, including the holes that drain oil back to the crankcase.

We've owned two Yanmars: 2gm & 3gm. Loved then both. Wondering why you tried the paint thinner trick?? Frequent oil & filter changes is the better idea. Some say 4 or 5 changes with a lubricating solvent like Marvel Mystery Oil additive, with a short warm up and run between changes can unclog a neglected engine. I've never tried it myself and have to say I'd like to hear more.

[PineyWoodsPete]

Originally Posted by Boatwright

Could be sludge loosened by the paint thinner is clogging your crankcase vent. The suggestion on removing the oil filler cap as a test may work, but it might be better to take off the valve cover before you run the engine again to clean up any sludge that may be blocking things up, including the holes that drain oil back to the crankcase.

We've owned two Yanmars: 2gm & 3gm. Loved then both. Wondering why you tried the paint thinner trick?? Frequent oil & filter changes is the better idea. Some say 4 or 5 changes with a lubricating solvent like Marvel Mystery Oil additive, with a short warm up and run between changes can unclog a neglected engine. I've never tried it myself and have to say I'd like to hear more.

Likewise, in our '93 FP Antigua 37. We babied them in the warm-up phase, but generally ran at 80% max revs to prevent cylinder head and exhaust valve carbonization, with occasional several minute run-ups to max revs. They were still running strong, sans smoking, at 4000 hours when we sold her in 2001.

I've also got to wonder what prompted the radical intervention of running the engine filled with a non-lubricating solvent - which seems to have led to the current situation.
Pete

[realem]

I have a 2GM20f that I recently installed as a used engine. I did have exactly the same problem blowing oil out the dip stick entry. The pressure would blow the dipstick out of the opening. After searching all the issue it turned out to be a kink in the vent hose back to the injectors. I cleared and changed the hose, no problem now

[Sonosailor]

Originally Posted by skybolter

The first thing that comes to mind is possible damage to the piston rings. Running with mineral spirits could easily cause damage which would result in scored cylinder walls. This would cause blow-by which would increase crankcase pressure which would cause what you are seeing. A compression test could be useful for diagnostics. Also, this engine is prone to exhaust elbow carbon clogging. I suppose a partially clogged elbow could elevate the backpressure and cause the condition you are describing...just a guess, though.

The mineral spirits were recommended for 20 minutes by a qualified diesel guy, as a means by which I might unstick the piston rings if that was the problem, and certainly as a means to dislodge sludge that might have been causing the engine to go through oil pressure senders every few weeks. It really did stop the dipstick problem for the 40+ hours since then, and the oil pressure sender has lasted as well. It was the first time I ever saw clear oil after even minutes of changing it. The boat did six hard hours as a charter boat before I became the new “captain”.

I have checked the elbow, and it looks like new inside - now buildup of carbon.

[Compass790]

Definitely dislodged sludge in your crankcase venting system could be a problem as suggested by other posters. Need to check/ clean & blow thru it.
Brave man running on mineral spirits with possible stuck rings. I'd keep a block of wood handy to shut off air supply if I tried that.
Lotta good suggestions in previous posts except maybe #5

[Sonosailor]

Thanks guys, but nothing new suggested yet.

Crankcase blowby: Those of you who know the engine know that it is tough to block and easy to check. No foam, no screen no filter; just a little baffled box on top of the valve cover that runs to a 3/8" short tube to a 3/16 or so opening downstream of the air filter in the air intake. No sign of a problem whenever this happens. The air filter is not saturated with oil, and there never seems to be a significant issue in the hose or the intake, wrt oil residue, well, maybe a drop in the hose, to be fair.

Occurrence: This doesn't happen every time I start the engine. I could go weeks without an issue, then bam: I uncover the engine to find the compartment in a *&^%ing mess. I could run it for days with the cap off, and possibly not have a problem.

Engine performance: The engine works great, starts easily, makes no funny noises; and delivers propulsion without complaint just like its sister in the other hull. It does make a little more smoke when quickly accelerating and when backing on anchor at 2000rpm (after the chain is already tight), than its sister, but not much.

Engine maintenance: Boat is used only 5 months per year in the Caribbean. Each layup involves a complete oil and filter change. I am a sailor, and long engine use only occurs when I am buddy-boating. It did this fall, and that is the only reason we have 40+ hours since the oil change.

Why the mineral spirits: Six years ago, this was happening a lot. A Yanmar guy in Guadeloupe said he was sure I had a faulty fuel pump filling the crankcase with diesel and that was doing it. He sold me a "rebuilt" pump, and I put it on. Indeed, it was not rebuilt, but did have the busted diaphragm. The fuel did go into the crankcase, did come out the blowby, and I had a runaway engine with diesel in the crankcase. I got the engine stopped, sorted it all out, stopped trusting dealers and counter-people, and put the old pump back. When I told it all to a seasoned Yanmar mechanic, he said I might find that I had fixed the oil problem by running it wildly fast with diesel as the solvent in the crankcase. He was correct, and I had no problem until last spring. The suggestion was stuck rings, which sometimes caused the problem, and the diesel unstuck them. I was told to increase rpm to decrease carbon in both the oil and the mixing elbow. I have, and certainly the mixing elbows are doing better.

Last spring, I not only had the oil spurting out twice, but had oil pressure senders malfunctioning regularly. Another qualified diesel mechanic told me to try the mineral spirits, but with the crankcase blowby sending to a pail. I did not run the engine hard, but just enough to get the equipment well rinsed. It worked for 40 hours: no oil pressure sender problem, oil pressure in the correct range checked with a guage, and no kicking out of the oil stick.

Now here I am again. Did I miss anyone? As always, I appreciate all comments. No matter what you write it stimulates the brains of the rest of us.

Also, I have to ask: What is the way that the crankcase venting gets up to the valve cover, to exit the crankcase blowby baffle and hose? Is that something that could become blocked and cause excess pressure in the crankcase that cannot get to the valve cover area?

[cal40john]

Originally Posted by Sonosailor

Thanks guys, but nothing new suggested yet.

Crankcase blowby: Those of you who know the engine know that it is tough to block and easy to check. No foam, no screen no filter; just a little baffled box on top of the valve cover that runs to a 3/8" short tube to a 3/16 or so opening downstream of the air filter in the air intake. No sign of a problem whenever this happens. The air filter is not saturated with oil, and there never seems to be a significant issue in the hose or the intake, wrt oil residue, well, maybe a drop in the hose, to be fair.

Occurrence: This doesn't happen every time I start the engine. I could go weeks without an issue, then bam: I uncover the engine to find the compartment in a *&^%ing mess. I could run it for days with the cap off, and possibly not have a problem.

Engine performance: The engine works great, starts easily, makes no funny noises; and delivers propulsion without complaint just like its sister in the other hull. It does make a little more smoke when quickly accelerating and when backing on anchor at 2000rpm (after the chain is already tight), than its sister, but not much.

Engine maintenance: Boat is used only 5 months per year in the Caribbean. Each layup involves a complete oil and filter change. I am a sailor, and long engine use only occurs when I am buddy-boating. It did this fall, and that is the only reason we have 40+ hours since the oil change.

Why the mineral spirits: Six years ago, this was happening a lot. A Yanmar guy in Guadeloupe said he was sure I had a faulty fuel pump filling the crankcase with diesel and that was doing it. He sold me a "rebuilt" pump, and I put it on. Indeed, it was not rebuilt, but did have the busted diaphragm. The fuel did go into the crankcase, did come out the blowby, and I had a runaway engine with diesel in the crankcase. I got the engine stopped, sorted it all out, stopped trusting dealers and counter-people, and put the old pump back. When I told it all to a seasoned Yanmar mechanic, he said I might find that I had fixed the oil problem by running it wildly fast with diesel as the solvent in the crankcase. He was correct, and I had no problem until last spring. The suggestion was stuck rings, which sometimes caused the problem, and the diesel unstuck them. I was told to increase rpm to decrease carbon in both the oil and the mixing elbow. I have, and certainly the mixing elbows are doing better.

Last spring, I not only had the oil spurting out twice, but had oil pressure senders malfunctioning regularly. Another qualified diesel mechanic told me to try the mineral spirits, but with the crankcase blowby sending to a pail. I did not run the engine hard, but just enough to get the equipment well rinsed. It worked for 40 hours: no oil pressure sender problem, oil pressure in the correct range checked with a guage, and no kicking out of the oil stick.

Now here I am again. Did I miss anyone? As always, I appreciate all comments. No matter what you write it stimulates the brains of the rest of us.

Also, I have to ask: What is the way that the crankcase venting gets up to the valve cover, to exit the crankcase blowby baffle and hose? Is that something that could become blocked and cause excess pressure in the crankcase that cannot get to the valve cover area?

The passages that allow the oil lubricating the valve train to return to the crankcase connect the crankcase to the valve area. If that were blocked oil would filling the valve area.

[Compass790]

Ok sorry I added nothing but it sounds like you have a rare problem to state the obvious.
Can you elaborate more on what happens with the oil pressure senders?
Are these just alarms or to oil pressure gauge?
I assumed your crankcase breather came from the crankcase rather than rocker cover as it does on our Yammer. Shuda checked first.
My GUESS is the crankcase pressure comes up thru the pushrod galleries but will check later on 2gm20 as I've messed up on breather pressure path.