1994 Mercruiser 4.3 LX, water in all cylinders

1994 Mercruiser 4.3 LX, water in all cylinders. Engine started normally, operated at high idle normally for 15 minutes, but when accelerated it missed a few times, slowed and quit. Would not restart. On examination, there was water in all cylinders. The engine is in an 18 foot runabout. There was no backwash, and there are no visible water leaks in the engine compartment. It is hard to believe that both head gaskets, or both exhaust manifolds, or both risers failed simultaneously. Is there a component that could have failed (thermostat housing on the intake manifold? single flapper for both cylinder banks?) that could have failed allowing water to enter the intake manifold and contaminate all six cylinders?

Re: 1994 Mercruiser 4.3 LX, water in all cylinders

Howdy,

It sounds like you could have a cracked intake manifold. You're going to need to look for anything that is common to all the cyls.

It is also possible that you still had a "backwash" in that there was enough water in either manifold that would have allowed water to get through (open)intake & exhaust valves and then into the intake manifold.....


When the engine quit it could have turned backwards a turn or two that would also allow water to be sucked into a cyl that would allow water thru an open intake valve and then into the intake manifold....

All of the above are just possibilities.

More possibilities:

Where is the water line compared to the top of each riser?
Was the boat sitting in still water or rocking/rolling in large waves/wakes?
Have you ever removed the risers and inspected the risers/gaskets etc?


Regards,


Rick

Re: 1994 Mercruiser 4.3 LX, water in all cylinders

HT32BSX115 said:

Howdy,

It sounds like you could have a cracked intake manifold. You're going to need to look for anything that is common to all the cyls.

It is also possible that you still had a "backwash" in that there was enough water in either manifold that would have allowed water to get through (open)intake & exhaust valves and then into the intake manifold.....


When the engine quit it could have turned backwards a turn or two that would also allow water to be sucked into a cyl that would allow water thru an open intake valve and then into the intake manifold....

All of the above are just possibilities.


Where is the water line compared to the top of each riser?
Was the boat sitting in still water or rocking/rolling in large waves/wakes?
Have you ever removed the risers and inspected the risers/gaskets etc?


Regards,


Rick

Click to expand...

I had the same problem this weekend. The boat was running fine then I stopped to pick up a tuber and it would not start. The water was pretty rouge. I got it home and pulled the plugs and sure enought it was hydralocked,water in all six cylinders. What would cause this? Just the risers?
More possibilities:

Re: 1994 Mercruiser 4.3 LX, water in all cylinders

scottx2 said:

I had the same problem this weekend. The boat was running fine then I stopped to pick up a tuber and it would not start. The water was pretty rouge. I got it home and pulled the plugs and sure enought it was hydralocked,water in all six cylinders. What would cause this? Just the risers?
More possibilities:

Click to expand...

My guess is, when you came to pickup the skiers instead of going to neutral and letting the engine idle, you just turned off the ignition. At which point the engine probably dieseled, sucked in water and died. Then the stern wave hit the back of the boat and went up the exhaust pipe past the shutters (aka flappers) if they were sticking or burned up, and straight into the cylinders. Probably both happened about the same time.