502 EFI Water in stainless manifold
 

Has anybody experienced water intrusion into a Merc 502 Gen 6,
415HP EFI engine with Stainless Marine Manifolds and Risers? Thanks

yes it happend to me turned out i had a cracked water jacket on my IMCO exhaust manifold, how old is the exhaust system?

It appears to be about 15 years old. Jerry at stainless and everybody else I have talked to says they have never experienced a failure with these manifolds. I thought it would be in the riser, but cannot find a leak with hot water.

I would pull them and have them pressure tested mine were about the same age i purchased them used and ran across a less than honest guy they were bad when he sold them to me and he knew it! Cost me about $5k by the time it was all done, I had the boat to a well respected mechanic, he and everyone else kept thinking head gasket or reversion and finally after the second engine milk shake a small shop near my home lake pulled the exhaust manifolds and tested them. So another $700 for new stock manifolds & risers and the problem was solved.

If you have thru hull exhaust and your internal flappers are burned out, it may be coming from there. External flappers are not 100% effective. You really need both.

Chris

you definitely have reversion with any motor that has an over lapping valve events. T he key is minimizing its effects. The S/m manifold with the short riser is no better and probably a little worse (as would most aftermarket manifolds w/ the short stainless riser) than the factory manifolds. The overlap in a stock 502 mag should be pretty minimal though. Do you idle for long periods of time thru no wake zones etc? Try to keep the revs up a little more and/or rev the motor up in neutral from time to time... if water reversion is actually the problem.

Thanks for the reply. I still have not found the "smoking gun" and HOPE it is just reversion. I tested the manifold and sent the riser to SM for testing. I will try and pressurize the block and heads this weekend. If evverything tests good, I will put everything back together and start it up and see what happens.