How is water getting in the cylinders of my 496Mag?!?!
 

Hey guys! I am getting very frustrated with my boat and I was hoping that you help me with some ideas.

The boat is a 2001 Formula 260BR with a 496Mag and Bravo 3. I bought it about three years ago with a little over 100 hours on it and it now has about 150 hours on it. The boat came from a saltwater environment but I use it in clean fresh water. I have had numerous small issues with the boat but have managed to get them resolved. I am having a hard time getting rid of this water ingestion problem.

I initially thought that I had a starter problem because the starter and flywheel would sometimes grind and the engine would fail to turn over. After a while I figured out that the motor was actually hydro locking and thats why the starter can't turn over the engine. Then I believe that the starter bolts would flex enough to let the starter gear and flywheel grind past each other.

What could be the potential causes of this hydro locking? The boat and motor are factory stock as far as I know. The motor runs well and the boat hits about 51mph which is right where it should run when I compare it to other Formula 260BRs. The exhaust does not have captains call. I believe the internals of the motor to be stock (cam, etc). I was thinking that this could be exhaust reversion or a friend suggested that could be a blown head gasket and that it could be coolant in the cylinders. What do you guys think? To compound the problem, I don't have a trailer so the work that I do to the boat has to be done at the dock unless I borrow a trailer. It doesn't hydro-lock every time that I run the boat but it is super frustrating to get out somewhere and be unable to get the motor restarted.....

Thank you guys VERY much for your time and insight into my problem!

Pull the exhaust manifolds and check for leaks.

What he said :grinser010: Especially check for trailing down from the riser gaskets both internally and externally. If you have rust stains on the outsides of you manifold risers, count on them leaking internally also. It could just be the gaskets on the risers/extensions and your manifolds may be okay. But if the riser gaskets look okay, you should have the entire manifold assembly pressure tested.

I thought the exhaust on the 496's was a dry joint between the manifold and riser?

Whoops, thinking 502, my bad. Have the manifold and riser pressure tested.

I think you need to find out if it is in fact hydrolock or some kind of starter issue or other issue.

When you have encountered this sitiuation, did you remove the spark plugs and then crank the engine to see if water was coming out ?

If you did:

Was it coolant or seawater coming out ?

Which cylinders did the water come out of ?

Do you have water/coolant in the engine oil ?

They are just like the 6.2s but the risers rot out and water runs in the manifold.

Thank you guys very much for your replies!

The motor definitely gets water in the cylinders. I take out the spark plugs and rotate the motor by hand (breaker bar on the crank nut) and fluid comes out of the spark plug holes. I have never noticed that it is coolant but I think that it is a possibility. I have never had milky oil so I don't think that the fluid/water is getting in there. I think, but I'm not positive, that the water has only come from the starboard cylinder bank.

My boat does not have risers between the manifold and exhaust elbow. It just goes manifold, gasket, turbulator, gasket, exhaust elbow. (Note: the turbulator is a stock Merc part, not something that was added) I believe that this joint is "dry" because there are no water passages in the elbow or manifold at that junction.

If you have water in your cylinders you have some water in your oil.You need to get that boat on the trailer and do a couple of oil changes as a flush.Then do a compression check to rule out head gasket.If that passes pull the side apart (exhaust) that the cylinders had water and start looking with water in your cylinders should be pretty obvious.

And buy a can of fogging oil (spray) when the manifold is of soak the cylinder and the exhuast port in the head.

Find out if it is coolant or sea water.

I agree that you most likely also will have some water or coolant in the oil, so you need to care of this as soon as possible so you do not ruin the engine.