Gentlemen,<br /><br />How does water get into the cylinder from the exhaust manifold? <br /><br />I have a '71 Mercruiser 140hp, 181ci. Last weekend, I overheated the motor to about 230F. I replaced the impeller this weekend, and tried to start the motor in the yard. It wouldn't fire at all, but cranked normally. I took out the plugs and did a compression test (150-180 psi on all cylinders), and noticed some water vapor spitting out the plug hole. Not much water, about 3 tablespoons or so (mostly on rear cylinder). <br /><br />After consulting this list, I removed the intake/exhaust manifold to look for cracks, gasket damage, etc., but found none. I did notice that the exhaust valve is lower than the water running through the manifold, separated only by a little rise between the manifold and exhaust port. When the manifold is full of water, what prevents it from filling the exhaust port and then the cylinder? <br /><br />I see that most here recommend replacing the manifold after overheating. Why would I do that? I don't see any obvious damage to the manifold or the exhaust riser, but can't understand what keeps the manifold cooling water out of the cylinders. Can someone explain why this would happen? My service manual doesn't cover this topic well. <br /><br />I did change the oil when I did the impeller, and didn't notice any water in it, but after an afternoon of cranking the motor in my yard, the dipstick shows a little water froth. Other than the flapper in the exhaust riser, is there any other moving parts on the exhaust side? Are there baffles between the exhaust port and water reservoir in the manifold? I don't see anything in there that looks like a baffle, but the boat is 35 years old, and it may have rusted away completely.<br /><br />Any advice you can offer would help me a lot.
