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Yanmar 1GM Water in Oil??

Oct 29, 2016
1,743
Hunter 41 DS Port Huron
My son and I have, as announced a few months back bought a new to us 1983 Soverel 33 with a single cylinder Yanmar 1 GM engine. My son has been working diligently on fixing the deck and hull areas that needed attention as well as a fresh coat of paint on the interior just to make her look nicer. Anyway he has started putting it back together in hopes of a launch with in a week or so. Last Wednesday we fired up the engine (after changing oil, oil filter and fuel filters) and surprisingly enough it rumbled to life pretty easily considering it had not been run for at least 4 years maybe 5.
I does appear that a new cutlass bearing is needed, we repacked the shaft log, but, after running the engine for a very short time last week we checked the oil and to our dismay the oil had gone milky.........now looking at the seawater pump assembly and the way it is driven off the end of the cam shaft we suspect that both the water and oil seals had dried up and water was allowed to pass thru the assembly into the crankcase.
My question to all you folks out there that have more knowledge than I could possibly acquire in a lifetime......... What are the possible avenues for water to enter the crankcase other than the seawater pump housing?? Would love to ensure that before we splash Aonbharr we have all the liquids staying in the right places.
 
Last edited:
Jan 11, 2014
7,629
Sabre 362 113 Fair Haven, NY
Head gasket or warped cylinder head.

Cracked internal oil channels in the block.

The gasket is what you hope for as it is probably the cheapest to replace.
 
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Likes: DayDreamer41
Jul 7, 2004
7,884
Hunter 30T Cheney, KS
A compression test won't be necessarily determine it but not a waste of time doing. It could be the gasket area around a water passage only.

Exhaust elbow?
 
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Likes: DayDreamer41
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@dlochner I sure hope that its only the seals on the seawater pump, the other options you mention sound expensive, especially a cracked oil passage, that would seem to be the end to the motor at that point. Head gasket wouldn't be too bad I guess. The OP said they winterized the boat before it was stored so lets hope for the best and thanks for your input @dlocher.
@Justin_NSA Thanks for the suggestion I think that elbow check might be next
 
May 24, 2004
6,744
CC 30 South Florida
Go ahead and repair or replace the raw water pump assembly. It will be one less thing to worry about. If after that you still have water intrusion then remove the cylinder head and check the head gasket. The fact that the engine started shows the single cylinder has adequate compression and that at least that part of the head gasket is good and could be indicative of the rest of it. Make sure you flush the engine before refilling with new oil as water remnants can remain in the bottom of the crankcase which could contaminate the new oil. You can use diesel fuel or Mystery oil for the flush. Also check the outside oil lines that run under the engine, they are prone to corrosion. Good luck.
 
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Likes: DayDreamer41
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@Benny17441 thanks for the input, I thought the same for head gasket, we rebuilt the pump yesterday my son will put it back in today, great suggestion on flushing the engine I am betting we will have to change to oil a couple of times to ensure that all the water is gone from the crankcase.
 
Nov 22, 2011
957
Ericson 26-2 San Pedro, CA
You should know that the raw water pump used on the 1GM/1GM10 is awful and requires frequent rebuilding, including replacement of the seals. They are most unreliable. Definitely get that taken care of first and see if it doesn't cure your problem.

You can either rebuild it yourself (there are YouTube videos that show how) or send it off to Depco Pump and they'll do it for you.
 
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Likes: DayDreamer41
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@Alan Gomes I have read many articles on the weakness of the seawater pumps on this motor which has me wondering about using an electrically driven pump to deliver seawater to the engine, we are in clean freshwater. We did rebuild the pump yesterday and my son is installing it today, I haven't heard from him yet on how successful this will be in eliminating the water-oil issue.
Thanks for your feed back
 
Nov 22, 2011
957
Ericson 26-2 San Pedro, CA
@Alan Gomes I have read many articles on the weakness of the seawater pumps on this motor which has me wondering about using an electrically driven pump to deliver seawater to the engine, we are in clean freshwater. We did rebuild the pump yesterday and my son is installing it today, I haven't heard from him yet on how successful this will be in eliminating the water-oil issue.
Thanks for your feed back
I own two of these engines and can say from my own experience that the sea water pump is the weakest link. That, and the mixing elbow. It's a pretty decent engine otherwise.

My main hesitation about going with an electric pump is that the flow rate would be constant vs. regulated by engine rpm. But perhaps others will weigh in with their thoughts on this.
 
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Likes: DayDreamer41
Jan 11, 2014
7,629
Sabre 362 113 Fair Haven, NY
Most water pumps are pretty robust and last a long time, however they do wear. How old is the boat and is this pump original? I doubt you can find an electric pump that can hold up as long. Another issue, is the motor will require power to keep the pump running. With mechanical fuel and water pumps the diesel can run by itself without electricity. Some diesels like the Volvo MD7A can be hand cranked to start, not sure about your Yanmar, but a 1 cylinder diesel should be easy to get going.

Mixing elbows are always a challenge on most boats, because hot water and hot exhaust gases are mixing in the elbow. Not a good combination. However, I doubt the mixing elbow is causing the water in the oil. It could happen, but it would be the result of the mixing elbow becoming so clogged with carbon and gunk that water backed up into the cylinder and past the rings. If that happened the motor would hydro lock. Nonetheless, do inspect the mixing elbow for carbon build up and rust through. A company near you HDI (?) makes nice SS replacement elbows.
 
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Likes: DayDreamer41
May 24, 2004
6,744
CC 30 South Florida
@Alan Gomes I have read many articles on the weakness of the seawater pumps on this motor which has me wondering about using an electrically driven pump ....
I personally like to be electricity independent on the engine. No electric fuel pump, no electric water pump. The water pump on the 1GM has gotten an ill reputation as people let them go before providing maintenance and repairs until they create another problem; but they are not that bad. Cleaning the surface for the insatllation of the seals is crucial.
 
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Likes: DayDreamer41
Nov 22, 2011
957
Ericson 26-2 San Pedro, CA
Most water pumps are pretty robust and last a long time, however they do wear. How old is the boat and is this pump original?

Mixing elbows are always a challenge on most boats, because hot water and hot exhaust gases are mixing in the elbow. Not a good combination. However, I doubt the mixing elbow is causing the water in the oil. It could happen, but it would be the result of the mixing elbow becoming so clogged with carbon and gunk that water backed up into the cylinder and past the rings. If that happened the motor would hydro lock. Nonetheless, do inspect the mixing elbow for carbon build up and rust through. A company near you HDI (?) makes nice SS replacement elbows.
Just to clarify my earlier remarks, which I can see could easily be misunderstood: I was mentioning the mixing elbow not as a cause for water in the oil, but simply in the context of one of the weak links with a 1GM. While all mixing elbows are subject to failure due to hot gases, corrosion, etc, the particular design on the 1 GM is especially failure prone and can easily lead to water getting in the cylinder. It requires regular inspection, even more so than is typical. As for the raw water pump on the 1GM, it too is much more failure prone than your average pump. Again, it is another weak link that is peculiar to that engine, beyond the normal failures associated with such parts generally.

Oh, and I should also add a third weak link to that engine--again, not related to the particular problem being experienced here. The mild steel oil lines are subject to corrosion, precisely because the lousy raw water pump is subject to frequent leaks and is situated immediately above a couple of the lines. Something else to keep an eye on. yanmar did switch to copper lines at some point, so depending upon the age of the engine the problem may be less acute.

Again, sorry for any lack of clarity on my part.
 
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Likes: DayDreamer41
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
Well we rebuilt the pump and we will see how that goes all surfaces were cleaned and it was reassembled only time will tell now. But I am going to have a look at the mixing elbow, who know how much gunk is in there. If the pump continues to be a problem (assuming this is where the water was entering the crankcase) then I may look at my options.
I don't believe that the variable drive speed as opposed to a constant speed would have much effect as the thermostat determines when to allow flow into the block otherwise it bypasses.
Thanks again all
 
Nov 22, 2011
957
Ericson 26-2 San Pedro, CA
Well we rebuilt the pump and we will see how that goes all surfaces were cleaned and it was reassembled only time will tell now. But I am going to have a look at the mixing elbow, who know how much gunk is in there. If the pump continues to be a problem (assuming this is where the water was entering the crankcase) then I may look at my options.
I don't believe that the variable drive speed as opposed to a constant speed would have much effect as the thermostat determines when to allow flow into the block otherwise it bypasses.
Thanks again all
Check the internal tube on the inside of the elbow for any pinhole leaks. That's where water can enter and do damage to the cylinder.

As for the pump, did you replace the seals? That would be critical. Again, you could get those seals from Depco Pump.
 
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Likes: DayDreamer41
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
@Alan Gomes Yes we bought the whole rebuild kit which included bearings, oil seal, water seal, snap rings, gasket bots and cover. The shaft is a separate order but it looked to be in good shape.
 
Nov 22, 2011
957
Ericson 26-2 San Pedro, CA
@Alan Gomes Yes we bought the whole rebuild kit which included bearings, oil seal, water seal, snap rings, gasket bots and cover. The shaft is a separate order but it looked to be in good shape.
Great! Hopefully that corrects the problem with water in the oil. I'll bet that it does. Please be sure to report back.
 
Oct 29, 2016
1,743
Hunter 41 DS Port Huron
OK all, again thanks for your input it's always appreciated.

To report back the rebuilt water pump was reinstalled today engine fired up and ran pulling water from a bucket and TADAH no water in the oil, so the lesson from all this is to keep an eye on the weep holes of the pump housing and should there be any water leaking from this housing time to rebuild....... before the oil gets ugly. I suspect that given the boat sat for (4) years the rubber seals became brittle, who knows maybe they were on the way out when the boat was put on the hard but we now have a running motor, next up, the cutlass bearing, she is getting close.