Water in exhaust manifolds

[chartersj]

Intake manifold or the intake manifold gasket would be my next guess. The stem cleaning is evidence of water entering during the intake stroke. GM engine blocks have the front portion of the intake manifold act as the cooling water cross-over.

Ok thanks. I assume that could get water in both sides? What about head gaskets? But what are the odds both are bad,,,,

 

[Scott06]

Ok thanks. I assume that could get water in both sides? What about head gaskets? But what are the odds both are bad,,,,

compression and or leakdown test will reveal bad head gaskets

 

[chartersj]

compression and or leakdown test will reveal bad head gaskets

Just checked compression, all were between 172 and 190 psi.
I ordered an Amazon borescope this morning,
And I’m buying a good set of exhaust manifolds and risers from a buddy today…

 

[Lou C]

If it were a leaky intake manifold, that would put water right in the oil since it would leak into the cam valley, I doubt that it would put water in the cylinders
Here's what you might do
If you can remove/install the manifolds and elbows as a unit, all assembled, you can remove the ones you have and prop each one level. Then hook up a garden hose to the manifold water inlet port, and turn on the hose about half way (don't need full pressure because these systems don't or shouldn't build that much pressure). Watch the ports that mate up with the cylinder heads for any sign of water. If there is a leak in a casting or the gaskets aren't sealing you should see it. If there is nothing at all, it could be condensation.
Or, when you get your borescope, run the boat on the water, get it good and warmed up, don't idle it too much and check them like I did. I used a fitting on the top of the OMC/Volvo exhaust elbow to slide the camera in. Small fitting but camera fit in perfect.
Last thing
what temp is your engine running at? If it never warms up when idling on the water hose (temp doesn't reach the rating of the thermostat) you will for sure get some condensation in the exhaust.
You should have a 160 stat if it's an EFI engine.
I have a 160 in mine, I tried a 140 stat because of all the blah blah about salt/calcium crystallizing in a raw water cooled engine (never really happened at all, I could see that with the heads off when I did my top end overhaul) and for sure I had condensation in the exhaust! So I went back to the 160 stat I always used.
Get a straight edge, and a set of feeler gauges, and measure the flatness even on new parts!
Run a thread chaser in the threads, make sure the bolts thread all the way in.
The condensation issue is such that Merc actually came out with the warm manifolds system where the manifolds do not get cooling water flow till the stat opens, the elbows always get it. Now what system does your engine have? Cold or warm?
OMC and Volvo always had the cold manifold system where one hose feeds the manifold and elbow, so their exhaust runs cooler but can get condensation.
If you have only one hose feeding the manifold/elbow it is the cold manifold system, if you have a separate hose for each one, it is the warm manifolds most likely. If you have the cold system then condensation is a definite possibility but if you have the warm, you should not see any water in there, unless the engine never warms up.

 

[chartersj]

If it were a leaky intake manifold, that would put water right in the oil since it would leak into the cam valley, I doubt that it would put water in the cylinders
Here's what you might do
If you can remove/install the manifolds and elbows as a unit, all assembled, you can remove the ones you have and prop each one level. Then hook up a garden hose to the manifold water inlet port, and turn on the hose about half way (don't need full pressure because these systems don't or shouldn't build that much pressure). Watch the ports that mate up with the cylinder heads for any sign of water. If there is a leak in a casting or the gaskets aren't sealing you should see it. If there is nothing at all, it could be condensation.
Or, when you get your borescope, run the boat on the water, get it good and warmed up, don't idle it too much and check them like I did. I used a fitting on the top of the OMC/Volvo exhaust elbow to slide the camera in. Small fitting but camera fit in perfect.
Last thing
what temp is your engine running at? If it never warms up when idling on the water hose (temp doesn't reach the rating of the thermostat) you will for sure get some condensation in the exhaust.
You should have a 160 stat if it's an EFI engine.
I have a 160 in mine, I tried a 140 stat because of all the blah blah about salt/calcium crystallizing in a raw water cooled engine (never really happened at all, I could see that with the heads off when I did my top end overhaul) and for sure I had condensation in the exhaust! So I went back to the 160 stat I always used.
Get a straight edge, and a set of feeler gauges, and measure the flatness even on new parts!
Run a thread chaser in the threads, make sure the bolts thread all the way in.
The condensation issue is such that Merc actually came out with the warm manifolds system where the manifolds do not get cooling water flow till the stat opens, the elbows always get it. Now what system does your engine have? Cold or warm?
OMC and Volvo always had the cold manifold system where one hose feeds the manifold and elbow, so their exhaust runs cooler but can get condensation.
If you have only one hose feeding the manifold/elbow it is the cold manifold system, if you have a separate hose for each one, it is the warm manifolds most likely. If you have the cold system then condensation is a definite possibility but if you have the warm, you should not see any water in there, unless the engine never warms up.

My engine has the cold manifolds. Only one hose goes to the bottom of each manifold, and 160 thermostat.
It is getting cool here now,, so I was idling the engine for the full 10-15 mins until I seen the thermostat open up then gave it only a couple small quick revs,,, maybe it is condensation,, I just want to be sure.
Can I put it back together, leave the hoses off the bottom of each manifold, start it up on the hose and let them drain into the bilge? Or is that telling me anything

 

[Lou C]

If you start it that way, they won't get cooling as they should, that can overheat the exhaust rubber hoses and flappers. I don't think that will do anything to solving your concern.
I bet your exhaust system is only at about 90-100* under those conditions, idle, cool day, cold manifolds, because that is how mine is even with the 160* stat, the engine just doesn't make that much heat, idling on the hose.
I recall Mercruiser did tests of the hot and cold manifolds, they found that the exhaust temp had to be at least 120* to burn off condensation.
To deal with this I run the engine at about 1200 rpm so it builds a little more heat which helps, it warms up faster. In salt water you can have the issue of sand or rust flakes holding the 'stat open and then it never really warms up.
If you want to get to the bottom of it, see if you can test them off the boat like I described.
Some like to fill the manifold with acetone off the boat with the elbow off, that will find cracks that water might not, but it doesn't tell you if the joint is sealing.
just be careful those cast iron parts are dang heavy!
I got lucky with the Barr exhaust I installed, I haven't had any leaks with it so far and I've used it approx 7 seasons, so will probably have to change them soon. I'll check em again with the borescope and see how it looks inside.