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Old 27-04-2017, 02:36   #1
sb1
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Yanmar 2GM20 oil exploding from dipstick hole

Hi folks,

I know something similar has been discussed in the past, but please bear with me. My Yanmar 2GM20 (one of them) builds pressure in the sump and blows oil out from the dipstick hole. The general consensus is blow-by and therefore dodgy piston rings or such, but the way the engine ticks over (very nicely) it really doesn't seem like it.

The breather hose is not blocked, by the way, nor does there seem to be any obstruction downstream from the breather outlet, but it is quite oily in the bonnet under the breather cover.

I suppose I will probably have to accept the expensive truth, but if anyone has "an alternative truth" I would be grateful to hear it. Could a faulty oil pump be to blame?

Cheers!

Damo
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Old 27-04-2017, 02:47   #2
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Re: Yanmar 2GM20 oil exploding from dipstick hole

Check the PCV valve - if there is one on this engine. but it does not need a lot of blow by to cause this issue, and the engine may well run fine.
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Old 27-04-2017, 04:24   #3
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Re: Yanmar 2GM20 oil exploding from dipstick hole

Crank case pressure should relieve through the breather on the rocker cover. The hose might be clear, but what about the valve built in to the cover itself? How much blow by do you get if you remove the oil fill cap?
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Old 27-04-2017, 04:38   #4
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Re: Yanmar 2GM20 oil exploding from dipstick hole

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Originally Posted by sb1 View Post
Hi folks,

I know something similar has been discussed in the past, but please bear with me. My Yanmar 2GM20 (one of them) builds pressure in the sump and blows oil out from the dipstick hole. The general consensus is blow-by and therefore dodgy piston rings or such, but the way the engine ticks over (very nicely) it really doesn't seem like it.

The breather hose is not blocked, by the way, nor does there seem to be any obstruction downstream from the breather outlet, but it is quite oily in the bonnet under the breather cover.

I suppose I will probably have to accept the expensive truth, but if anyone has "an alternative truth" I would be grateful to hear it. Could a faulty oil pump be to blame?

Cheers!

Damo
Nasty - only time I've seen something similar was in the cooling system of a car with a blown head gasket. Not much better than rings but worth a look if you're in there...
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Old 27-04-2017, 05:25   #5
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Re: Yanmar 2GM20 oil exploding from dipstick hole

We had this and thought it was a bigger issue turned out the dipstick was just a little too loose AND our exhaust hose was old and has actually delaying aged internally and was blocking exhaust creating excessive back pressure.
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Old 27-04-2017, 06:36   #6
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Re: Yanmar 2GM20 oil exploding from dipstick hole

There is no PCV valve on a Diesel, or I have never seen one anyway.
However there is almost always a form of air oil separator in the valve cover that of course keeps oil from being blown out, often it's just a mess of steel wool or similar, and it can become dirty and block airflow.
I'd take the valve cover off and soak it in a bath of mineral spirits and specifically look for sludge on the part where the blowby hose connects.
Of course too much oil will certainly cause this, you sure its not overfilled, and it has the correct dip stick?
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Old 27-04-2017, 06:41   #7
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Re: Yanmar 2GM20 oil exploding from dipstick hole

A PCV valve is a form of restricted orifice, its used on engines that can have a high vacuum in their intake manifold, like a regular gasoline engine, during periods of high vacuum, like coasting down a hill with the throttle closed without a restriction, the engine would pull too much air out of the crankcase and maybe pull oil out too etc.
A Diesel has no throttle valve, and therefore has no vacuum and I think not a PCV valve, just a hose to relieve pressure
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Old 27-04-2017, 08:16   #8
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Re: Yanmar 2GM20 oil exploding from dipstick hole

SB,
It would be helpful to know how many hours are on your engine and what has been the maintenance schedule since you've owned it. When you remove the oil fill cap when running, is there blowby(smoke/oil) or is it only from the dipstick? Is there any restriction in your hot exhaust(mixing elbow)? Is your oil filled to the proper level? These answers would be helpful to further diagnose your problem. I have seen hundreds of engines with blowby and have never seen anything other than smoke emanate from the dipstick or oil fill cap when the piston rings/compression was severely compromised.
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Old 27-04-2017, 08:29   #9
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Re: Yanmar 2GM20 oil exploding from dipstick hole

We had this happen some 12 years ago, fortunately it was no more than the rubber on the dipstick having disinterested. Hopefully it is no more than this for yourself
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Old 27-04-2017, 08:35   #10
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Re: Yanmar 2GM20 oil exploding from dipstick hole

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There is no PCV valve on a Diesel, or I have never seen one anyway.
However there is almost always a form of air oil separator in the valve cover that of course keeps oil from being blown out, often it's just a mess of steel wool or similar, and it can become dirty and block airflow.
I'd take the valve cover off and soak it in a bath of mineral spirits and specifically look for sludge on the part where the blowby hose connects.
Of course too much oil will certainly cause this, you sure its not overfilled, and it has the correct dip stick?
Agreed! And make sure it's just oil in the crankcase, coolant or fuel getting in the crankcase will show up in the beginning as over full on oil..
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Old 27-04-2017, 08:37   #11
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Re: Yanmar 2GM20 oil exploding from dipstick hole

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(snippage)
Of course too much oil will certainly cause this, you sure its not overfilled, and it has the correct dip stick?
+1 on proper oil level. It's easy to overfill oil on many direct drive inboard engines, due to the tilt. The "Full" mark on the dipstick may be result in a serious overfill condition. Check the manual for the proper "full" level for your degree of tilt.

Another thought, is the seal at the top of your dipstick still intact?
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Old 27-04-2017, 09:59   #12
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Re: Yanmar 2GM20 oil exploding from dipstick hole

Since piston rings are already indicated, a compression test is the next step.
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Old 27-04-2017, 10:00   #13
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Re: Yanmar 2GM20 oil exploding from dipstick hole

Take off the oil fill cap and put your hand over it to see how much pressure. If your twin screw compare to your other engine.

Yanmars apparently put the bottom of the dipstick tube below the oil level in the pan so if you get excess pressure it will blow the oil out.

Lost an engine when the steel wool in the breather hose got plugged and the oil pressure alarm failed.. Blew all the oil into the engine room until the engine siezed.

Bill
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Old 27-04-2017, 10:09   #14
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Re: Yanmar 2GM20 oil exploding from dipstick hole

I had one this problem, on an old Volvo MD17HD, and it was caused by an head gasket that was brocken. The exhaust on one cylinder was leaking gas, and blowing into the base of the engine. On teltale sign was the oil that became very dirty(black) and smelled like exhause .
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Old 27-04-2017, 11:11   #15
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Re: Yanmar 2GM20 oil exploding from dipstick hole

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Originally Posted by Moontide View Post
Yanmars apparently put the bottom of the dipstick tube below the oil level in the pan so if you get excess pressure it will blow the oil out.

Bill
A lot of marine engines do, its done that way so the dip stick tube can be used to extract oil.
One problem is what you said about blowing out oil, another is incorrect oil level readings.
If you shut down the engine and let it cool overnight and check the oil the next morning, it will often read way high, this is because the tube is sealed and has one end under the oil level, as it cools the air contracts and pulls the oil up the tube giving you a false high reading. If you check it again, you will get the correct reading, so always wipe the stick the first time and then check the level
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