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Bf90 with water in the oil ...

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Kmcclain

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So I need some help here, I bought a boat from a gentleman that has an issue with water in the oil. I've been an auto mechanic , although my knowledge stops in the early 2000s( haven't worked in the trade since then).the engine is a 2001 bf90. When I brought it home, I changed the oil and filter, ran the engine in a tank for about 30 minutes. Fresh oil was tan like grandpas coffee! Compression check showed 150 in all cylinders. I talked to a few of my buddies that work at different marine shops, and asked them what they thought. One said he had only seen one engine in the shop that had this issue and they couldn't find the problem. The other said they have had several in , and , a few years back they received a bulletin that said Honda wanted them to start using a gasket maker on the power head gasket (between power head and mid section) . So I ordered a gasket set, tore down the engine to a short block. I left it apart for several days. Kept going back to it and inspecting everything. I ran the head down to my local machine shop, can't find any issue with the head. I took a straight edge to he head, block, mid section , and oil pan. I couldnt seen any issues. I reassembled the engine with new oil pan gasket, power head gasket, head gasket ,ect. I ran the engine last night with fresh oil, again about 30 minutes. It appeared to have a very very little amount of water so I thought I fixed it. I figured just residual water from before. I pulled the oil plug today to drain the oil and replace with fresh oil, and low and behold , grandpas coffee again! I'm at loss here . If anybody has any ideas , I would greatly appreciate it. Thanks, Kevin
 
Firstly, has this motor always been used in saltwater? If so, although I have not seen this on a BF90, I have had a BF135 corrode through the inside of the water jacket around the cylinders in the block, through to an oil passage. This was a one off case on a motor that had had a hard life in saltwater with inadequate flushing. The only way to see this is to scrape all the build up from inside the outer wall of the cylinder block main water jacket, if there is an issue you will find spots of deep pitting. Apart from that I have only once seen the wall between the exhaust and the oil pan corrode through on the mount case. If this is a fresh water only motor, then you'll be looking for cracks rather than pitting, a little hard to find. Good luck.
 
Ian & KMCCLAIN,

Just thinking - does the 90 also have a water tube that goes from the water pump up through the oil pan with a sealing grommet on the upper end like the 225? If so, that would seem to be a productive place to look.
 
Previous owner said it was fresh water only. The water jackets are nice and clean. Hour meter on the console reads 324 hours. So I assume engine only has 324 hours.
 
The water tube runs outside the oil pan. It has 2 machined holes that seem to cool the exhaust pipe.so I would assume that the mid section around the oil pan holds water while engine is running.
 
Yes, there are water jackets round the oil pan. I am thinking the water is getting in somewhere in the mount case area, this is where I would be concentrating the inspection . The only common issue these engines had was excessive water pump leakage which resulted in water pressurizing in the drive shaft tube forcing its way up past the top seals into the flywheel housing, but that resulted in starter failure.
 
So an update, I went and bought a flush bib from my local dealer, i ran water though like I was flushing the engine, with the oil plug removed and I've got water coming out the oil pan . Removed the lower unit, mid section, oil pan , and oil pick up tube. Turned the hose back on, and I've got water coming out the main oil pick up section ( where the oil pick up tube mounts). So power head is coming off tomorrow... I'll keep you guys updated . Thanks so much for the replies so far, I really appreciate it ...Kevin
 
Kmcclain said:
So an update, I went and bought a flush bib from my local dealer, i ran water though like I was flushing the engine, with the oil plug removed and I've got water coming out the oil pan . Removed the lower unit, mid section, oil pan , and oil pick up tube. Turned the hose back on, and I've got water coming out the main oil pick up section ( where the oil pick up tube mounts). So power head is coming off tomorrow... I'll keep you guys updated . Thanks so much for the replies so far, I really appreciate it ...Kevin
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Hey Kevin I just rebuilt A BF90 myself from top to bottom everything was running fine. After a half hour runtime in the water for its this first test I got the milkshake in the oil pan. If you were able to the fixtures are found with the problem was can you let me know please thanks in advance.
 
Pointless throwing it back together without finding the problem, suggest professional pressure testing if issue is not obvious
 
Kmcclain said:
So an update, I went and bought a flush bib from my local dealer, i ran water though like I was flushing the engine, with the oil plug removed and I've got water coming out the oil pan . Removed the lower unit, mid section, oil pan , and oil pick up tube. Turned the hose back on, and I've got water coming out the main oil pick up section ( where the oil pick up tube mounts). So power head is coming off tomorrow... I'll keep you guys updated . Thanks so much for the replies so far, I really appreciate it ...Kevin
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It sounds to me like you have this problem on the run. BUT - if you can't pin point and repair the issue, it's not that hard, or expensive, to just replace that block (or short block) with a used one.

I'm with Iang6766 here. If you can positively identify the issue and repair it, fine, but there's no way I would go through all the time to reassemble and test again without some confidence.
 
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