I have bought a boat with two 454 s bluewater engines. When I first looked at the boat I could not find any signs of water in the oil. Then when I got it home and ran them for about an hour on the hose, I have now found water in both engines, more in one than the other. Upon this finding I rebuilt the one motor and found no leaking head gasket. Now I have noticed when I pull the risers off water is sitting in the exhaust ports. mostly the right side of each motor for some reason. I have called around locally and can not find anyone to pressure test my manifolds and even called Hardin Marine. Thus I am wondering since it seems someone has recently modified the exhaust if it is possible that the flapper is back splashing water into the exhaust. I am saying that because the flapper is only 6 inches away from the end of the riser. My exhuast is a little differently on the VIP the have is exiting at a 90 turn down under the platform. So there is no way to install flappers at that point so I am susposing that is why they insalled it where they did.

sounds like your manifolds may be junk. Stock ones are known to leak at the riser joint, or rot away and leak in general especially in salt water.

Make sure you didnt smoke the water pumps by running them on the hose for an HOUR.

Do the engines have stock cam shafts? If not it could definitely be a reversion issue. In regards to pressure testing, I did mine myself. Plugged up all the water connections except one and then connected it to my air compressor. I then submerged the entire manifold in a 55 gallon drum of water. No bubbles = no leaks

Good luck
Jim

GLM manifolds that look to be not that old no signs of roting. They are the orginal cams mercruiser 7.4 mpi year 2000

hey 502ss how did you plug up the maniforld to the riser holes?

I didn't have to, mine are dry pipes. The water transfers from the manifold to the riser via an external hose but in your case a simple aluminum plate bolted to where the riser bolts should do the trick, even if you get a little leak you should still be able to see any other air bubbles, just make sure you have enough air compressor volume

I am wondering I have the boat on a trailer. The trailer is sitting level, the boat is about level bow upward a little. I think if the boat were sitting in the water the bow would be a little higher. The exhaust seems to be level meaning not any flow toward the transom. Could this have caused so much water in the manifolds? Has this happen to anyone else? Looking I may have room for 2" riser extension. A merc mechanic told me I have L 29 engines and they are famous for sucking in water in the exhaust. Anyone heard of this before?

I think I may have found the issue today i took off all four risers. I checked them for level and noticed that who ever installed them left the paint on the exhaust manifolds. I cleaned them up sanded them down to bare metal with a orbital sander, installed new gaskets with head gasket sealer. I going to let it sit overnite and dry and try again tomorrow.

update I have tried everything I know and still getting water in my engine, one is rebuilt not happy about that. I am getting ready to throw in the towel. I have been fighting with this boat for 6 weeks now. I wish I could only find someone who could put me at ease and pressure test my exhaust manifolds. It is had for me to believe that all four are bad, but I do not know any history of this boat. I would hate to spend 900 to change exhaust on just one engine and still find water in the oil. Any help or suggestion Please I can not believe this boat is going to beat me!

Well I am not getting much feed back here on this issue, I have made many calls and it seems to be that I have revision issue and the motors are sucking up water from the stock exhaust riser. I am going to try longer stainless steel risers. So I am looking to buy