Need Cooling System Guru for 2000 era F90-F115

[colin.slade]

Hey All,

Looking for some advise from owners of 2000 era F90-F115's that have dealt with water in cylinders.

Noticed milky oil at the start of the season. Cylinder #2 spark plug seemed cleaner than others and a compression test indicated it low (90psi) while all others were 150. Suspected head gasket but when I took it apart there was no obvious leak. Had the head surfaced, pressure tested, and valves ground, new seals. Re-assembled, seemed like it was running OK but noticed oil started to look watery. Engine started running rough and found water in cylinder #4. Compression was good across the board but I suspected I messed something up, I was using a suspect torque wrench and figured I wreaked the new head gasket? Removed, no obvious leaking, checked the block to confirm it was flat. No cracking visible anywhere on block. New head gasket, re-assembled and found it was running like shit right off the bad; not firing on #4, water on the spark plug. AHHHH!!!! When I took things apart cooling passages didn't seem too corroded...

From what I've read it sounds like the exhaust manifold is supposed to be dry and a water leak into the exhaust could cause water to get pulled into the cylinders. If this is the case seems like it would be most likely to happen to the bottom cylinder? I'm going to do a leakdown test to see if there is air leaking into the water jacket but assuming it tests OK can I get some input from people more familiar with the cooling systems on older F90-115's?I assumed that water would be purposely added to the exhaust at some point similar to an inboard but I don't know where that should happen (at what point should the exhaust be wet?). There is an exhaust cover on this motor; I had previously removed it, cleaned it, and re-installed with a new gasket. No obvious damage to either side of the assembly but does this cover separate water and dry exhaust and should it be double checked?.

Below the power head I see there is a gasket between the powerhead and exhaust guide. Do you think if the exhaust guide is corroded and/or the gasket has failed that water could get into cylinder #4? I'm reluctant to tear into things further at this point unless I am confident it could be a cause as the gaskets here are crazy expensive (already into it for $500+ in gaskets!!!). Luckily my times not worth anything

If anyone has any suggestions on most probable places to check next please let me know!

Thanks,

[colin.slade]

Bump! Surely someone here is familiar with the cooling/exhuast system on 2000' era yamahas...

[colin.slade]

Time for an update. I pulled the lower unit off (what a terrible time that was, had to cut off one of the lower vibration mounts).

Separated exhaust guide, oil pan, muffler, downtube, ect. Broke a couple bolts in the process but the gaskets all looked pretty good and except the oil pump (old style and the lower seal portion looks like its starting to rot out) there was no major corrosion; the lower unit seems fine.

I made a plate and rubber gasket to bolt underneath the power head blocking off the exhaust and water passages. When I apply low pressure to the water flushing port I have leakage out the spark plug holes. The leakage comes out of different cylinders depending on the position I put the engine in so I assume my leakage path is between water jacket and exhaust and it's coming of out the spark plug holes when a given exhaust valve is open).

My head was rebuilt, surfaced, and pressure tested. The block seemed flat and true with a precision straight edge. There was no obvious leakage path when the gasket was replaced (twice!!!!). I replaced the exhaust cover gasket but took it off again to inspect and it looks very good. It's a pretty bad leak, I can hear it easily and feel the air moving past my finger. Any ideas or recommendations to narrow down this leakage path?

Cheers!

[panasonic]

So you said in first post that the head was pressure checked. In your second post you said you made a plate that blocked the exhaust on the bottom of powerhead. So only thing left to do is take cylinder head off and make a plate to block exhaust on the top of cylinder block and pressure test the block.

Must be hole corroded thru between water jacket and exhaust chamber in the block or a crack.

Going to be tough to find that...