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Mercruiser 3.0 with dreaded water in the oil

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Redrider6604

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Last fall I picked up a boat in a trade. 1987 cheetah with the 3.0. Interior was shot and needs to be done which I do that for a living so that’s why I got it. Engine runs great and so forth. I noticed when fist running it, it had water leaking from the back of the engine. So pulled the motor out and replaced the welch plug behind the flywheel. When I had the plug out which it was rusted , I flushed the engine with a water hose. After putting the flywheel back on, went to drain the oil and it seemed like 3 gallons of water and oil pouring out. Anyways, I installed the engine back in the boat so I could do some tests. I’ve only ran it on muffs and haven’t put it in the water because it needs bellows. I run it every couple of days and oil level never changes. I have changed the oil multiple times just to see and it keeps looking like coffee with creamer in it. Pulled all the plugs and compression is 160-163 on all four with wot. Did a leak down test and that passed. Have done a smoke test on the cooling system for about 4 hours and never had a leak. That was with oil cap off, drain plug out, dip stick out, oil filter off and the lifer/ push rod plate off and the machine maxes out with pressure which shows no leaks. I made a complete block off plate for the exhaust riser and left the exhaust hole open just to see if smoke would come out of the exhaust but I’m getting nothing. Would appreciate if someone can guide me in the right direction.
 
Redrider6604 said:
Last fall I picked up a boat in a trade. 1987 cheetah with the 3.0. Interior was shot and needs to be done which I do that for a living so that’s why I got it. Engine runs great and so forth. I noticed when fist running it, it had water leaking from the back of the engine. So pulled the motor out and replaced the welch plug behind the flywheel. When I had the plug out which it was rusted , I flushed the engine with a water hose. After putting the flywheel back on, went to drain the oil and it seemed like 3 gallons of water and oil pouring out. Anyways, I installed the engine back in the boat so I could do some tests. I’ve only ran it on muffs and haven’t put it in the water because it needs bellows. I run it every couple of days and oil level never changes. I have changed the oil multiple times just to see and it keeps looking like coffee with creamer in it. Pulled all the plugs and compression is 160-163 on all four with wot. Did a leak down test and that passed. Have done a smoke test on the cooling system for about 4 hours and never had a leak. That was with oil cap off, drain plug out, dip stick out, oil filter off and the lifer/ push rod plate off and the machine maxes out with pressure which shows no leaks. I made a complete block off plate for the exhaust riser and left the exhaust hole open just to see if smoke would come out of the exhaust but I’m getting nothing. Would appreciate if someone can guide me in the right direction.
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Would pressure test the cooling system drain block off inlet and outlet put 15-20 psi should hold pressure.

It is possible that there is moisture in the engine and it never gets hot enough to burn it off if thermostat is stuck open or missing… but I would think several changes would get rid of it. May be crack in manifold or corrosion at manifold to elobow is leaking water back in combustion chambers and past rings . If you run it and let it sit, take plugs out spin see if water comes out.

Would be willing to bet that it was frozen and that why plug popped on back of block. In which case they knew that and you got hosed on the trade. Im might go break some kneecaps if I were you
 
I would say your smoke test on the cooling system has a flaw somewhere in it's execution...being there aren't any details its hard to say where...

Given your conflicting descriptions, I would conclude water has to be mixing with the oil. agree with the pressure test, though I'd be inclined to stop at 10PSI, at least for the initial phase... Sometimes, it is easier to test the pieces than the whole system...

Would agree with the Frozen conclusion....and modify the budget accordingly...
 
Dieter said:
Would pressure test the cooling system drain block off inlet and outlet put 15-20 psi should hold pressure.

It is possible that there is moisture in the engine and it never gets hot enough to burn it off if thermostat is stuck open or missing… but I would think several changes would get rid of it. May be crack in manifold or corrosion at manifold to elobow is leaking water back in combustion chambers and past rings . If you run it and let it sit, take plugs out spin see if water comes out.

Would be willing to bet that it was frozen and that why plug popped on back of block. In which case they knew that and you got hosed on the trade. Im might go break some kneecaps if I were you
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The engine didn’t have a thermostat in it which I knew. So installed the thermostat and gasket and did it at 15 psi and never dropped. It did raise some because the temperature outside got up to 91 degrees. Held good for 4 hours yesterday and dropped a 1/2 of a psi by this morning which I can say it was temperature variation. So I am wondering if it’s just condensation in it. I’m going to reinstall the motor and get it lined up and give it another try. Hopefully it will work. I appreciate your input.
 
Redrider6604 said:
The engine didn’t have a thermostat in it which I knew. So installed the thermostat and gasket and did it at 15 psi and never dropped. It did raise some because the temperature outside got up to 91 degrees. Held good for 4 hours yesterday and dropped a 1/2 of a psi by this morning which I can say it was temperature variation. So I am wondering if it’s just condensation in it. I’m going to reinstall the motor and get it lined up and give it another try. Hopefully it will work. I appreciate your input.
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If the pressure test included the manifold and your elbow is in good shape and not leaking at gasket joint (file flat) , then yes would think the issue is not having a thermostat and not getting hot.

Usually when thermostat it taken out it is a crux for some other BS they couldn't diagnose or fix like a bad water pump impeller or clogging due to impeller bits or rusted manifold. Maybe it was stuck and they didn't have a replacement.

Buy a bunch of cheap oil like rotella T4 or super tech and several filters. You only need to put in like 3 qts, let it idle and get hot change it until it runs clear, may have to do that once or twice to get it clean enough to take on the water and get it good and hot for a long run, should boil it off
 
Yesterday (Feb 18) I was doing an oil change in my 3.0 Mercruiser inboard (1993 Bayliner Cuddy, 20 ft) and I got the dreaded water in the oil bc I pumped out milky oil of 1-1/2 gal and the oil capacity is usually 1 gal. My repair plan: (1) Change out exhaust elbow gasket (2) Change out thermostat (3) change out head gasket. I had this wonderful 32 year old boat for 26 years so these gaskets needed replacement anyway. If I discover that I have a cracked engine block, I will buy a kicker motor to continue fishing since my water skiing days are over since I am in my mid-70's. Not worth it to pour too much money into a 32 years old cuddy boat that I mainly use to camp on the water for 2 glorious nights and 3 days. My questions: (1) Is my 3 step repair plan a sound one? (2) Does anyone have experience adding a kicker motor to their fiberglass 20 ft boat?
 
i'd be inclined to check the exhaust elbow before doing anything else.

My old man boat a 20ft boat decades ago with a kicker on it...the guy he bought it from installed it and used a bracket bolted thru the transom...
 
makomark said:
i'd be inclined to check the exhaust elbow before doing anything else.

My old man boat a 20ft boat decades ago with a kicker on it...the guy he bought it from installed it and used a bracket bolted thru the transom...
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Took apart the exhaust elbow and discovered that gasket was intact and there is no sign of water going down to the engine by looking into the large cavity which is full of dry soot. My next step is to replace the head gasket which looks like a one day or two day job. If I discovered a cracked block, then I will take my time replacing it. A new barebone block cost about $1000 but does not include the pistons and connecting shaft. I prefer a short block rebuilt which includes the pistons and connecting shaft but I have yet to find one under $2500, Mostly a barebone block for about $1000 or a complete rebuilt with heads about $3500. I need to add $2000 for labor because engine replacement is something I do not want to do at my age. Meanwhile I will look at my kicker engine option as an interim. I got about 26 years of boating joy and engine use without any problems until now so I am not complaining. Paid $8,000 for the Cuddy boat so I got my money worth. I think my repair limit is $5,000 but I keep coming up with a $6,000 repair estimate. If the problem is a blown head gasket, I will be happy as heck.
 
Since the "COVID era", prices have gone thru the roof for damn near everything...my favorite oil filter source used to be $4 for a brand name filter for my truck....I looked last week and cringed when I read $7.49....thats one helluva an increase in a couple years....
 
Attached is just ONE COMPLETE plug and play engine on Face Book Market place. I search this 5 minutes ago.

125 hrs, $2000.00 asking price. If this is what it says it is this could give you another 30 something years of use with no issues.
4 cyl FB markt Place.jpg
 
kghost said:
Attached is just ONE COMPLETE plug and play engine on Face Book Market place. I search this 5 minutes ago.

125 hrs, $2000.00 asking price. If this is what it says it is this could give you another 30 something years of use with no issues.View attachment 34455
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Thanks for the info. I will replace the head gasket and carefully examine the block for cracks after I pull the heads off. If there is a crack, I am leaning toward the new barebone block and reuse the pistons and connecting rod with new rings and connecting rod bearings. I will post photos if I need to take that path. I decided to DIY everything since I am retired and I have time to do this.
 
looks like a new intake/exhaust manifold and a new elbow solved my problem. I also decided to change out my fuel pump, carborator, coil, spark plug wires, distributor and my 32 year old 3.0 mercruiser is running pretty good. Sweating bullets about a cracked block or a blown head gasket but the best case scenario occurred. I will watch my temperature gauge like a hawk in the future. Happy ending for sure.
 
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