Found water in every spark plug of my 305 Mercruiser

[bodnice]

Hey Team,
I took my boat out and noticed it was running hot immediately so I turned around. I figured my water pump inverter was in need of a change. As it cooled and I started to take it into the dock, it was running a little rough so I stopped again thinking it was hot. I went to start it again and it sounded like a vapor lock. It would not turn over. At home, I took out the 8 plugs and everyone had water on them, some more than others. I turned the motor several times and some rusty water shot out of them. They're drying out now.

My mechanic, over the phone, diagnosed it as a bad intake manifold that allowed water in. Would that hit every plug? What else would allow both side get water in? I thought I warped the head or something until I had the same problem on both sides in all 8 plugs. Mechanic said he'd change the intake manifold gasket for $350.00 but if that' not it then he'll keep moving on down the engine YIKE$

This is a 1988 Mark Twain with a beautifully kept 305 IO.

Thank You!

 

[Bondo]

Ayuh,...... Welcome Aboard,...... Do you boat in saltwater,..??

 

[QBhoy]

3 main suspects here.

it’s very unlikely but not impossible, that you have been unlucky enough to have both exhaust manifolds or risers to rot through at the exact same time. I don’t think so though.

you’re intake manifold is bad and allowing water to all 8 cylinders

or a mix of either or after winter and you’ve frost damage of manifolds, intake or exhausts or both sides of the block have cracked.

whatever it is...it’s something common to all cylinders or you’ve been very unlucky and had rot or frost to both sides.
most likely is the only thing that’s common to all. The intake manifold.

 

[bodnice]

Okay - I didn't mention that this boat was crammed in my garage all winter here in Arizona so weather isn't a factor. I didn't factor in the 5-10 minutes the boat idled while I was parking the trailer so it probably ran longer than I imagined hot... but I never heard any knocking of any kind. I think it still would be nearly impossible to crack both sides but I don't know for sure. What kind of tests can be done to determine that? Any suggestions? Thx

 

[Bt Doctur]

I took my boat out and noticed it was running hot immediately so I turned around

Is this the 1st run of the season. ? The water flow in the manifold should only be at the 2 front ports in the head, so it`s doubtful the entire intake is cracked.

it was running a little rough so I stopped again thinking it was hot. I went to start it again and it sounded like a vapor lock. It would not turn over.

At this point my guess is you got it got hot enough to take out the head gaskets

And find a better mechanic

 

[Bondo]

What kind of tests can be done to determine that?

Ayuh,...... A compression, 'n leak-down test will show a bad head gasket,.....

 

[Lou C]

In order for the intake to put water into the cyls it would have to be cracked right between the water passage and the intake passage. If you are in Az and in freshwater it’s very unlikely that either the intake or exhaust manifolds rotted out. It could be that but most often if they crack from freeze damage it usually puts water in the cam valley and into the oil. A compression test will often show head gasket problems but not always. I had 2 blown HGs with normal comp test results but water in 2 cyls and water in the motor oil.
what you can do:
do a comp test
drain the water out of the engine
air pressure test the cooling passages
remove the thermostat housing and inspect the intake interior for cracks

 

[Scott Danforth]

Okay - I didn't mention that this boat was crammed in my garage all winter here in Arizona so weather isn't a factor. I didn't factor in the 5-10 minutes the boat idled while I was parking the trailer so it probably ran longer than I imagined hot... but I never heard any knocking of any kind. I think it still would be nearly impossible to crack both sides but I don't know for sure. What kind of tests can be done to determine that? Any suggestions? Thx

it gets below freezing in AZ, even in the garages. depending on where you are, if your motor filled with fresh water was at 26 degrees for about 8 hours, you would have froze and cracked the block

 

[Rick Stephens]

● Garage insulated and heated?

● How was the boat winterized before parking?

● Manifolds and block drained?

I would think it more likely that the manifolds are cracked from a freeze than that something in the motor put water into every cylinder. Alternatively, if you no longer have functional exhaust shutters and you were moving along at a good clip and chopped the throttle, that could have filled the exhaust manifolds with water which would then get into every cylinder.

Lots of possibilities here. I would probably start with a pressure test of the cooling system, which can be a PITA to figure out how to plug inlets and outlets and hook up a tester. But worth the effort before tearing anything down. Once you start opening up the motor it is too late to pressure test it.

Rick

 

[achris]

...And find a better mechanic

This....

I guess from the second or third post that you were running it on the hose, without watching the temp gauge... As BT suggested. It got hot enough to take out both head gaskets, because you didn't check the water pump inverter before first running it, or even look at water flow....

BTW, Vapour lock will not lock an engine up, vapour lock just stops fuel getting to the carb. The engine will still crank just fine.

Chris........