[azboatman]

Hello All. Can someone please help me out here... I have a Mercruiser V6 4.3L Alpha one. Few month prior I was out on the lake running the boat with no issues. Relaxing in the water with engine off...when I went to start it I heard a huge clunk and the engine froze up. Long story short, I removed the spark plugs and found water coming out of one of the spark plug connection holes. I understand water cannot compress, therefore seizing. With all spark plugs removed I cranked the engine over and got all the water out. (in this situation it damaged my starter which I replaced). I did a compression check on all six cylinders and they all checked out fine....so I figure I dont have a blown head gasket...right? Replaced spark plugs, wires, battery, starter...tested boat out on lake for couple hours, no issues.

Yesterday, in Lake Havasu, running the boat, working great. Again, relaxing in the lake...engine off. went to start it up and CLUNK...repeat! Removed left side spark plugs and again water came out of the spark plug hole....removed all plugs, blew out water and engine started fine and ran fine. Shut off boat again, restarted - seized again. Needless to say, before I damage the engine anyfurther I am not taking the boat out until I get this issue fixed.

I did not see any water in oil (checking dipstick). Could this be an exhaust manifold issue? Can there be a one-way valve or flapper inside there that can go bad? Engine is 10 years old. Appreciate some advice...thanks.

[WetWilly]

Hi azboatman,

It's possible for the manifold, the exhaust elbow, or the gaskets between the manifold and the exhaust elbow or a tired or burned out water shutter valve to be the culprit. I would remove the left exhaust elbow and rubber coupler to the lower "Y" pipe and examine the manifold and elbow for signs of cracking, corrosion or bad gaskets and the water shutter (located at the top of the "Y" pipe). You can find this information in the Exhaust System section (7) of the 4.3V6 Service Manual.

Good luck,
WetWilly

[jasfiveo]

Second that....Just had this happen....exhaust shutters were gone causing water in the cylinders. Some clunk or thud noise (correct term is hydro lock or something of that nature). If the shutters are bad when you try to crank the boat you are letting water in and you get the lock up. Definitely check the shutters.

[azboatman]

WetWilly and JasfiveO........thanks for the quick response. I will check out the manifold and related parts. The service manual I have "SELOC" is very general and vague. None of the engines or parts look like my engine. Know where I can get a better one?

[jasfiveo]

I only had the owners maunual that came with the boat so while I was doing research I came across mercruiserparts.com. After entering my motor and drive specifications it will populate a sublist for all the parts (ie drive system, starting system, exhaust system, etc.). It has detailed diagrams (same ones used by my marie repair center) showing you all the parts. It helped me alot. Give it a look.

[azboatman]

Originally Posted by jasfiveo

I only had the owners maunual that came with the boat so while I was doing research I came across mercruiserparts.com. After entering my motor and drive specifications it will populate a sublist for all the parts (ie drive system, starting system, exhaust system, etc.). It has detailed diagrams (same ones used by my marie repair center) showing you all the parts. It helped me alot. Give it a look.

Thanks jasfiveO....I will try that site.

[Hyperryd]

You should be able to find the service manual in the Engine Maint. and Repairs section. The first section in dark blue has copies of the service manuals for Mercruiser and Volvo drives. I believe your engine is on page three of the Mercruiser manuals. Willy states above that it is in section 7 of that manual.

[1999Mariah]

I just replaced the exhaust manifold + riser + shutter on mine, I have a 4 cylinder, but I'm pretty sure you just have 2 of what I have for the riser/shutter portion, should be pretty easy to take off/check out and put a new shutter in there, quick + inexpensive...two words that don't ordinarily go with boat ownership..

[azboatman]

Hey guys, thanks for all the info. I found out you guys were right, it was the butterfly flapper (shutter) in the left side exhaust manifold elbow. Its was ripped in two. I decided to replace both sides and get it over with.....flapper was not cheap though....$50.00 per flapper (piece of rubber with metal in it).

I will take it out on the lake probably on Sunday. Should work great now. Thanks again.

[WetWilly]

Hi azboatman, just click here and it's all at your finger tips, don't forget to scan through the other pages too

WetWilly