Yanmar 2GM - water in oil - help!

[dr_c]

I have the head off of my 1st-generation Yanmar 2GM (an aftermarket 'freshwater' installation) and am looking for some advice. Frankly, I'm wondering if I'm headed down the right path.

After a hard start this past fall, the motor ran for a few minutes before throwing a 'low oil pressure' warning - once I shut her down, she had a lovely muddy-looking dipstick. Oil in water. Great. I quickly assumed I needed a head gasket.

I immediately did an oil change and fired her up, again - she started right up, but, unfortunately, within a few minutes, the low oil pressure warning came back on and the oil was slightly-muddy-looking, again. I dredged the oil pan with a magnet - didn't come up with any metal.

So this morning I pulled the head - no obvious signs of leakage on the head gasket, but I don't expect signs, necessarily. But then I got to thinking about the low oil pressure. . . could the oil pump be messed up? Is the block cracked? What the heck is going on to cause low oil pressure?

Could a blown head gasket account for both water-in-oil and low pressure? I'm torn between reassembling with fresh gaskets and seeing what happens . . . and calling the engine half-disassembled and pulling the damn thing. Thoughts?

Thanks,

Tony

[sailorchic34]

With the GM series the oil to the head is fed via an external pressure pipe, so odds are the low oil pressure is not caused by a blown head gasket as there is no pressurized oil passage through the head gasket. Could be caused by a sticking oil bypass valve, a worn oil pump or a crack in the rockers somewhere.

More likely the oil bypass or oil pump. The oil bypass valve is built into the stud the oil filter screws on...

[Dulcesuenos]

Im gonna guess you could have pulled the coolant cap off while it was running and see if you get exhaust or compression bubbling out. Also did the oil level increase or coolant level decrease when you ran it ? If the oil is turning brown (not just black) sounds like coolant. As the engine heats up something could be expanding to cause the coolant/ compression loss. Did you see the oil pressure gauge start to fluxuate wildly after a few minuts? if the oil flow to the top end is all external there could still be oil returning internaly thru passages that go thru the head gasket and that could still be the issue even though the head gasket looks fine.

[sailorchic34]

Ah, but the oil returning to the sump from the rockers via gravity drain, so would not effect oil pressure. Low oil pressure could be caused by a spun bearing too.

I'm wondering if the low oil pressure is caused by the water and or foaming caused by the water/ oil mix. I assume oil pressure is good till after a few minutes, so perhaps its the water. Which would take a really large leak BTW.

Water in the oil is most likely a blown head gasket or a cracked block.

With the head off see about adding water to the water jacket and see if it drops over time (once its full to the near the cylinder top).If the water drops its a cracked block. If not its probably a head gasket

[GordMay]

Greetings and welcome aboard the CF, Tony.

[dr_c]

Thank-you very much for all of the replies. I needed the sanity check.

As you both speculated, oil pressure was fine for a few minutes before dropping enough to trigger the idiot lamp. I haven’t noticed any oil-in-coolant, just evidence of coolant-in-oil, so am hoping that the low oil pressure is caused by the water or foaming. . . is this realistic?

I really like the idea of filling the water jacket with coolant and seeing if the level drops; although, after sitting for a few months, the coolant level did not drop enough to notice (remove cap, stick in finger, yup – coolant, recap). Assuming the block passes this check, I plan on:
1) Taking the head to a machine shop to be checked for cracks and ‘level.’
2) Replacing the oil bypass valve. Easy enough to do and a ‘suspect.’
3) Replacing the exhaust mixing elbow (looks OK, but I understand this is a good idea, since it’s apart)
4) Reassembling

I’m tempted to leave the oil pump alone since, after changing the oil and (briefly) running the engine, the oil pressure light didn’t come on right away. Not to mention that having the head off doesn’t seem to improve the accessibility of the oil pump. Anyone have experience replacing the oil pump on this motor?

Thanks – and please cross your fingers for me that a ‘spun bearing’ is NOT involved. . . .

-Tony

PS - Gord, thanks for the welcome. When I was thinking about where to ask this question, I googled 'yanmar' and 'Gord' to come up with the appropriate forum. . .

[sww914]

The water in the oil will cause low oil pressure. Water is much thinner than oil.
You need to determine where the water is coming from. It could be a blown head gasket but that's not the only place. You've already guessed a cracked block. That would likely only be the effect of major overheating or a bad casting. I've never seen a Japanese engine block fail due to poor quality. It could be a cracked head as well. Since it's off you can have it checked at a machine shop pretty cheaply.
You could have water from the exhaust making it's way up through the exhaust manifold, through the engine's open exhaust valves and into the cylinders. Sometimes with enough time it can all drip past the rings and into the crankcase. It could also be a failed raw water pump seal if your raw water pump is gear driven like mine is on my Perkins.
If your engine has a heat exchanger to cool the oil that may have failed too.
I hate to sound like a dick but you have to find the problem and fix it. Assumptions won't help you.

[Cheechako]

I'm not sure you should get an oil pressure alarm from water in the oil. Sounds to me like you have a bad oil pump and/or other issues for the water ingress. It sounds like this occurs real fast.... not a good sign.

[gjordan]

The grey/brown grey paste that forms when an engine is run with water in the oil is thick enough to reduce circulation and cause(among other things) low pressure readings. Since the head is off, have it pressure tested at an automotive machine shop. Figure out a way to test for a leaking oil cooler(if you have one)? Water pump leaking into the sump? All of this has been mentioned already , but should be checked. Something that I dont think has been mentioned is to check and see if you can pull the over pressure relief valve from the oil filter mounting bracket. It may or may not be possible, but it will need a good cleaning to get the grey goop out. Please let us know what the solution turns out to be. It might help the next guy._____Grant.

[HappyMdRSailor]

OK sailorchick... I am now finally convinced you are a dude living in your moms basement impersonating a female.... There have just been too many EXTREMELY detailed diagnosis and help in Sooooooo many threads.... (All of the above should read: "I am extremely impressed with your knowledge and thought processes")

Originally Posted by sailorchic34

Ah, but the oil returning to the sump from the rockers via gravity drain, so would not effect oil pressure. Low oil pressure could be caused by a spun bearing too. Bearing possibly, but we have a hard time diagnosing ... Does the oil pressure lower after a few minutes as the oil warms??? Or... Your thought below....

I'm wondering if the low oil pressure is caused by the water and or foaming caused by the water/ oil mix. I assume oil pressure is good till after a few minutes, so perhaps its the water. Which would take a really large leak BTW. I'm going to hop on this train with you.... Aerated oil causing low pressure....

Water in the oil is most likely a blown head gasket or a cracked block.

With the head off see about adding water to the water jacket and see if it drops over time (once its full to the near the cylinder top).If the water drops its a cracked block. If not its probably a head gasket I like the filling test, but may not eliminate block do to heat/vibration opening crack...., may give false positive due to evaporation (maybe top off water jacket passages with 100% AF or light oil? Have the head pressure tested while it is off....

I'm not familiar with the "aftermarket fresh water install" but these symptoms yell " leaking seal in the seawater pump"

My 2 cents that haven't caught up with inflation yet.....

[Cheechako]

Originally Posted by gjordan

The grey/brown grey paste that forms when an engine is run with water in the oil is thick enough to reduce circulation and cause(among other things) low pressure readings. Since the head is off, have it pressure tested at an automotive machine shop. Figure out a way to test for a leaking oil cooler(if you have one)? Water pump leaking into the sump? All of this has been mentioned already , but should be checked. Something that I dont think has been mentioned is to check and see if you can pull the over pressure relief valve from the oil filter mounting bracket. It may or may not be possible, but it will need a good cleaning to get the grey goop out. Please let us know what the solution turns out to be. It might help the next guy._____Grant.

Yeah... but this seems to be happening almost immediately. Some kind of catastrophic leak going on...
"...I immediately did an oil change and fired her up, again - she started right up, but, unfortunately, within a few minutes, the low oil pressure warning came back on "

[Jesse]

If "aftermarket freshwater install" means the engine was preveously raw water cooled the water jacket could be leaking into the oil sump due to rust or corrosion compromise. The increased pressure of a fresh water system can do this to a converted engine.

[sailorchic34]

Originally Posted by HappyMdRSailor

OK sailorchick... I am now finally convinced you are a dude living in your moms basement impersonating a female....

I'm not familiar with the "aftermarket fresh water install" but these symptoms yell " leaking seal in the seawater pump"

Ah rats, My secret is out

Well from about age 6 onward I watched my dad when he fixed anything on the car. I was a pretty good tool getterer too. Besides having a general engineering background, I have a curiosity about how everything work, So I tend to read just a whole lot. Plus I have the Yanmar GM series service manual . I also learned hands on engine repair with a 71 VW bus and a Triumph Spitfire. Weird Girl I know.

The water engress almost has to be a bad head gasket. The aftermaket fresh water cooling system, if its yanmar is basically the same components as the regular 2GM20F.

[perchance]

Make sure the vented loop on the water injection line is working. They can cause water to siphon back through the exhaust and enter the crankcase through any cylinder with an open exhaust valve.

[Nor'Sea 27]

Have you cleaned and inspected the mixing elbow to be certain the water/exhaust separations are intact?