1987 3.0L water in oil

[Ypt14flyr]

Need advice. Bought this Four Winns w/ 3.0 Merc I/O and evidence of water in oil. I'm a good engine mechanic but no experience in Marine engines. We've done extensive reading on this engine and there are no exterior cracks anywhere, in the 'well known' places. We replaced impeller in out-drive, changed engine oil, and test run. 1st go-around, Found rear core plug blown out, so pulled engine and fixed that. Engine back in boat, test run then took to river. Engine froze up after about 10 Min. Back to shop, pulled engine, removed head. Found no obvious (water to oil) passages in head gasket. (Possible blow thru between #2 / #3 cyls but prior compression was tolerable ie: 155, 135, 155, 155, so head gasket not problem. (and no signs of rust on top of pistons). Leak checked manifold as best we could, cold, and no leaks found. Head and manifold intake ports show some rust in one pair mainly.. And here also, no visible signs of cracks.. but again we don't think this has anything to do with water in oil. (Maybe chasing 2 problems?)..
We did find substantial 'other' damage inside. All rod bearings toasted so badly they melted. The mains look OK. All 4 rods now junk also. Pistons look OK.
Original question / problem. We do see some rust at bottom of cylinder bore(s) (2), and have read that these blocks can crack 'inside'. We saw one video showing crack at this location. We need to find a way to check the block inside. It's now completely bare. I guess we just need to plug all 'holes' and blow in air and do the soapy water trick?
Trying to decide if this thing is worth fixing. Crank is bad at rod journals also. We had the head 'serviced' and have all the gaskets to rebuild but now we may be holding the bag?. Advice please.

 

[Bt Doctur]

water thru the intake manifold? manifold cracked.
exaust and intake ports in head 3, 4 cyl. rusty,
head gasket blown between the 2 cylinders
whats your location?

 

[Lou C]

You def had a blown HG and that could be the source of water in the oil, I also see evidence of water leaking to the bottom of the exhaust passage in the exhaust manifold. If you have a good auto machine shop that will do a marine engine let them magnaflux the block & cyl head. Then they can measure the cyl bores etc & decide if it’s worth rebuilding.

 

[Scott Danforth]

if you are running over 4600 RPM for a length of time, you can warp the head.

 

[kenny nunez]

Usually there is a pinhole near the rear of the block on the bottom of the water jacket. That is the thinnest part of the casting. If you have an engine stand fill the water jacket with water then blow air under the jacket area and you will probably find the leak.

 

[Bondo]

Trying to decide if this thing is worth fixing. Crank is bad at rod journals also.

Ayuh,...... Welcome Aboard,...... It'll be cheaper, easier, 'n quicker to find a good running take-out motor from or in a rotten hulled donor boat,.....

 

[Ypt14flyr]

I'd like to believe the water in oil prob is 'just' the head gasket, but I'm seeing no evidence of blow thru between any of the passages in the head gasket, the head, or the block. (Although the head gasket is the 'crappy' metal one I've been warned about). Am I missing something? I poured some lacquer thinner in the rear water jacket area, near what appears to be a large scratch, and see no leak thru, but just a start. There is a band of rust in the #3 and #4 cylinder walls below the piston area that looks suspicious, but again can't find any cracks.

 

[Lou C]

maybe there....
What did the underside of the cyl head look like in that spot, is the block deck and cyl head flat and level when measured with a straight edge and feeler gauges (less than .003 variation?)

 

[cyclops222]

Warped head ? DIY damage during last overhaul.
Abused engine all the way. No confidence on parts used or installed correctly. AS Jonny Cash asked. How high was the water momma ?

 

[Ypt14flyr]

I saw that and suspected that area.. but as I mentioned the compressions were 155, 135, 155, 155 and so no real evidence of blow by between those 2 cylinders.. (#2 and #3 would have to drop the same, and prob below 100 Lb).. and that wouldn't have anything to do with water in the oil anyway, would it?.
I bit the bullet and took the block to the best engine builder in this area for cleaning and Magnaflux. Can't wait to hear if he finds a crack. He did point out a couple areas in block to suspect, (In general with this engine type), but no real signs of rust in those areas, so crossed fingers. But if block isn't cracked that would just leave another mystery, unless we are left to 'assume' the head gasket was leaking water to oil somehow. Need to find the actual source of this problem. Any more comments are welcome.
(I already had the head rebuilt and it's sitting at the ready. Hope I didn't jump the gun). Also bought a new head gasket that looks like a much better product. Sierra brand. Apparently these 3.0L blocks are scarce, and I still might have to find a complete engine, or at least a another block, depending on the outcome, but thanks all for your input.

 

[cyclops222]

I have had air bubbles in the radiator after the engine fully warmed up. None with room temperature startup.