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Old 23-03-2016, 11:05   #1
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Yanmar 3gm30f oil loss

My 2004 3gm30f with about 2000 hours on it has recently started losing oil at a pretty fast rate. Will top off to the high point on the dipstick, and it will be near the low point after about 12 hours of motoring. I've probably added 2 quarts of oil in the last 30 hours.

It otherwise still runs great, always easy starting, well maintained and kept spotlessly clean. Always fed polished fuel, recently replaced injectors. Had the head off a few years ago and no glazing. Never idled and always run fairly hard. Oil changed every 50-60 hours with Rotella 15W-40.

There are no oil leaks and no blue smoke in the exhaust, so I'm not sure where the oil is going. Also have not noticed any difference in operation since the oil loss started. Still runs smooth. There's always been a fair bit of soot buildup on the transom, but never any noticeable smoke. Always figured the prop was a bit oversized for the boat and the cause of soot buildup was a tiny bit of unburnt fuel.

Hoping some other's can chime in with suggestions on what to look for. I'm thinking
-clear out exhaust manifold
-check to make sure breather is not plugged

Currently in Georgetown, Bahamas. If anyone knows a good mechanic around here, I might happily give them a shout after doing some tinkering myself.

Thanks!

Ryan
s/v Soma
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Old 23-03-2016, 11:27   #2
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Re: Yanmar 3gm30f oil loss

Put it on a diet of Seafoam if you can find it there.
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Old 23-03-2016, 11:54   #3
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Re: Yanmar 3gm30f oil loss

Does this engine have an oil cooler? If so, check for leaks there. Otherwise, rings and/or cylinders and/or valve guides and/or valve seals are worn. 1 qt. per 12 hours is a lot.
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Old 23-03-2016, 13:05   #4
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Re: Yanmar 3gm30f oil loss

We have a 3HM35F, almost the same engine as your GM, and on our 2010 trip to the Bahamas had the same symptoms.

From my wife's blog Irish Eyes to the Bahamas for March 22, 2010:

"In Vero Beach I noticed that our oil pressure gauge read no pressure (like almost 0) although the alarm had not yet sounded. I told Bill, and he shut the engine off and checked the oil. Although low, there was still oil in the engine. Whew. Bill looked back at his log and realized the engine had been using much more oil than usual since the last oil change. We hadn’t noticed any strange engine noises or clouds of exhaust, but we decided when we got to Miami we would go to the local Yanmar dealer, Anchor Marine, and have a mechanic look at the engine.

"Bill called Anchor Marine while we were motoring through Miami. He talked to the Service Manager who asked if the engine started easily (yes), was it making funny noises (no), or emitting embarrassing clouds of smoke (no). His advice was to buy some oil and go to the Bahamas. No matter what might be wrong, the fix would be the same: overhaul or replace the engine. Since that would take a couple of weeks and $$$$, we decided to follow the guy’s advice. Also, Anchor Marine is a working boatyard in a pretty poor neighborhood on the Miami River and not the sort of place where you go on long quiet solitary walks. I could envision several weeks confined to my bunk staying out of the mechanic’s way while he worked making a greasy mess of my home. We bought 10 gallons of oil."

Now for the rest of the story...
By the time we got back home we had burned 12 gallons of Rotella, all with no smoke, easy starting, and no expensive noises. A local Yanmar mechanic and I pulled the engine, I drove it to Mack Boring in Union NJ, they rebuilt the engine, and the mechanic and I reinstalled it. The tech at Mack Boring reported that the cast iron rings in the aft cylinder were corroded into the aluminum piston perhaps from salt water entering that cylinder at some time.

I have an Excel spreadsheet of the oil consumption during the trip. A quart lasted 6 to 8 hours.

There was no blowby from the crankcase vent from the rocker arm cover to the air intake. There was no pressure on the oil dipstick hole. The exhaust elbow was changed with no effect.

The engine seemed to have been dragging oil up the cylinder wall into the combustion chamber and burning it.

Last year I dropped by Anchor Marine in Miami to get some parts and left them $20 for their break shack coffee fund as my way of paying them back for some of the best advice I have ever gotten from a marine supplier -- "Buy some oil and go to the Bahamas."

Irish Eyes
Black Point, Exuma
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Old 23-03-2016, 13:41   #5
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Re: Yanmar 3gm30f oil loss

They are noted for cracked pistons on the lower portion of the lower piston ring land. Mine was hard starting but ran fine once going.
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Old 23-03-2016, 14:24   #6
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Re: Yanmar 3gm30f oil loss

Yep, one or more stuck/ broken oil control rings. The engines can easily burn a quart in 20-30 hours with zero smoke. Had that happen on mine, but it got hard starting because all the rings on one piston were broken. From cracked ring lands.

The fix is the same (rebuild) so take lots of oil and have fun. Note that a 3gm will start and run on two cylinders. But it will be hard starting.
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Old 23-03-2016, 14:30   #7
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Re: Yanmar 3gm30f oil loss

I have a 2GM20, hard to start but runs great. Sometimes just tries to run on 1 cyl until the second gets going. Sounds like I might have some piston/ring issues.
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Old 23-03-2016, 14:37   #8
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Re: Yanmar 3gm30f oil loss

If it's worth anything average oil consumption for a new aircraft engine is a quart every 10 hours.
They are different designs of course, being intentionally "loose" as well, a seized engine on a airplane usually ends badly. Only reason I bring it up is to illustrate that yes a proper running engine can consume quite a bit of oil and not smoke.
But truly with a Diesel (in my opinion), if it starts easily, makes good power and doesn't smoke excessively, it's not broken.
I wish I had a buck too for every engine that I have seen "fixed" by a good, long, hard run, I've seen rings reseat and stuck rings free up from a hard run.
Run the snot out of it for an hour, starting with full oil and of course keeping an eye on temp etc.


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Old 23-03-2016, 15:21   #9
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Re: Yanmar 3gm30f oil loss

Quote:
Originally Posted by a64pilot View Post
If it's worth anything average oil consumption for a new aircraft engine is a quart every 10 hours.
To put oil in the engine on my Pacific Seacraft, I have to remove half of the cockpit floor to get hands on access to the fill hole in the rocker arm cover. On the way back from the Bahamas in 2010 I worried that I might have to add oil while underway in a seaway, maybe at night. I rigged up a funnel and a few feet of vinyl hose so that I could add the oil from inside the boat's cabin. I used it more than once.

When I read your note, I had visions of a wing walker pouring a quart of oil into the port engine of an airplane in flight at 200 kts. I'm still chuckling.
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Old 23-03-2016, 15:53   #10
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Re: Yanmar 3gm30f oil loss

Thanks for all the insight yall.

Good to hear that the engine should keep running if it is in fact the broken oil control rings or similar. The engine has also been starting a little funky the last couple pulls..turns briefly, then stops for a split second before kicking over..almost like it's getting hung up on something every so slightly. Initially thought it might be a loose batt connection, but no. Still starts up at nearly the push of a button though.

I've currently got about 6 gallons of Rotella onboard. Will be stocking up on some more before leaving Gtown!

wsmurdoch, incidentally, I was anchored out at Black Point a few nights ago before the run to Georgetown when I first really noticed the dramatic oil consumption. Also believe I was docked next to your boat a few years back in Oriental. Your grandson was living aboard for the summer if I recall correctly. Remember the PS34 Irish Eyes. Small world.

a64pilot, I like where your heads at with just running the snot out of the thing. Will put it thru it's paces here after this front finally passes thru

Ah, boats
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Old 24-03-2016, 04:19   #11
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Re: Yanmar 3gm30f oil loss

The Atomic 4 folks pour some Marvel Mystery oil over their pistons after haul out to stop the rings from seizing in carbon deposits. Seafoam is a decarbonizer. I suggest adding some to each quart of oil, and running the engine hard to break the seizures in the rings.
In the fuel it prevents varnishing of the pump and such.
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Old 24-03-2016, 05:33   #12
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Re: Yanmar 3gm30f oil loss

Quote:
Originally Posted by wsmurdoch View Post
When I read your note, I had visions of a wing walker pouring a quart of oil into the port engine of an airplane in flight at 200 kts. I'm still chuckling.
Sort of a mute point as we aren't sailing with aircraft engines, but the following formula is used to determine the max allowable oil consumption for Lycoming aircraft engines

0.006 x BHP x 4 7.4 = Qt./Hr.

so running the numbers a 300 HP Lycoming is allowed to burn .97 quarts an hour and still be airworthy. To certify an aircraft, the engine has to carry enough oil so that at max allowable consumption the aircraft will run out of fuel before the oil level gets to an unsafe level.

Back in the day I've been told that large radial engine powered transport aircraft had oil tanks and oil could be pumped into the engines, actually oil tanks as they are dry sump engines, in flight, and I think the B36 the engines could be accessed from within the wing in flight.

We have become used to modern automotive engines that will run for 200 hours and seemingly not burn a drop of oil, but I read a study published years ago by Brits that showed when an engine wore to the point to where it began to consume measurable amounts of oil, upper cylinder wear dropped drastically, theory being the rings and piston are being lubricated better now that some oil is getting by.

My 4jhe will burn a half a quart to a quart in 100 hours, and I like that it burns some.
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Old 24-03-2016, 05:36   #13
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Re: Yanmar 3gm30f oil loss

Sony has a good point in running the snot out of it, a bottle of seafoam just might break the rings loose if carbon is what has them stuck.
I'm not normally an additive type of person, but It might help.

The way you describe the funky starting sure sounds like hydro lock, but it's not from oil as that would smoke like crazy, but you sure there is no way water is getting into a cylinder?
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Old 24-03-2016, 09:19   #14
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Re: Yanmar 3gm30f oil loss

The down side to "running the snot out of it" if it's a cracked piston is you may score the cylinder wall..... making the rebuild a much bigger job. Mine was not scored and just needed honed and new piston/rod assy.
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Old 24-03-2016, 10:33   #15
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Re: Yanmar 3gm30f oil loss

Skylark's 3GM30F also consumes quite a bit more oil when I motor for extended periods at over 3000 RPM. If I keep the revs down below 2500, the oil consumption drops to almost zero.

I noticed this when the engine only had 500 hours on it.

I just check the engine oil before every start.

I have used Seafoam in the oil not for any specific reason other than just to "baby" the engine and I have used Mystery Oil in my autos' fuel and engine oil. On my 1966 Volvo, the Mystery Oil did such a good job of cleaning, the engine seals started leaking. New seals fixed that.
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