A basic understanding of the reasons for engine water ingestion

[Dave S]

BoatTest.com produced this video with Chuck Thurman of Crusader Engines where he explains in a very simple manner the main causes of water ingestion. It looks like they have some proprietary methods of dealing with it as well. Although he doesn't mention riser/elbow gasket failure, we know this is another cause of water ingestion with Mercruiser at least. However in looking at the design of the Crusader Risers on that video, it looks like they have a one piece riser which may eliminate that problem.

http://www.boattest.com/videos_home...usader&clip=crusader_new&width=400&height=300

 

[midway]

He said they are running a completely closed cooling system, so you have antifreeze solution running through the exhaust and engine, that should keep the manifold and risers running a lot longer, no corrosion to eat them away or cause gaskets to leak.

 

[PlayDate]

Dave,

Sounds like they have a handle on it but why has it taken 9 years to resolve what appears to be a simple problem. After all, if it truly is a cam problem, that is a $50 GM assembly change..... at most. Big blocks are off the GM truck block assembly line.


If it is purely temp differential due to fresh water cooling then that is Crusader and Mercruiser's responsibility since they engineer those systems. It's just hard to believe that they would pull the old engines out, slap new ones in with the exact same cam and exhaust configurations hoping for a different result.

-John

 

[Dave S]

Nolan..........You are probably correct that the FWC system solves a lot of the corrosion problems if you also run the system thru the risers. I would think though they still have to flow raw water downstream of the riser to cool the exhaust hoses.


John........It beats the heck out of me why it took so long to get a handle on these problems as well. It also appears to me that besides the cam issue, Crusader seems to have a done a better job than Merc with the design of their exhaust systems especially since he mentions they have a "proprietary" method of eliminating the problem of water ingestion due to valve overlap.

 

[fwebster]

Not so fast............

Most Mercruiser water ingestion problems that happen occur because of a riser or riser to manifold joint failure. By far, most riser castings that fail do so because they corrode from the exhaust passage into the water jacket and not the other way around. Perhaps this is mostly a salt water thing, but we see just as many FWC cooled engines with bad risers as we do sea water cooled. The reason is because the exhaust passage is filled with ambient salt laden air right off the water even when the boat is at rest. When you fire up the engine, rust particles flake off exposing new "meat". Then when you shut down the corrosion process begins all over. Sooner or later, the casting gets thin and it begins to seep.

 

[Dave S]

Not so fast............

Most Mercruiser water ingestion problems that happen occur because of a riser or riser to manifold joint failure. By far, most riser castings that fail do so because they corrode from the exhaust passage into the water jacket and not the other way around. Perhaps this is mostly a salt water thing, but we see just as many FWC cooled engines with bad risers as we do sea water cooled. The reason is because the exhaust passage is filled with ambient salt laden air right off the water even when the boat is at rest. When you fire up the engine, rust particles flake off exposing new "meat". Then when you shut down the corrosion process begins all over. Sooner or later, the casting gets thin and it begins to seep.

Frank,

I don't doubt that occurs especially on saltwater Merc engines. But from what I can see in that video, the only water being circulated in the Crusader Riser appears to be only from the FWC system (note the two hoses on top of the riser). If that's the case, it really should eliminate the corrosion problem altogether. Like I said, seawater probably has to enter the exhaust somewhere to keep the hoses cool but maybe that is done aft of the riser itself. I really would like to know more about those risers they use as the design appears that it may be superior to Mercs.

Dave

 

[fwebster]

Dave,

You missed my point........The Crusader risers may have antifreeze running in them but the exhaust passage is still connected to the muffler and exhaust plumbing and eventually ends right above the water outside the boat. That means on salt water boats the exhaust passage....not the cooling passage...is completely full of salt laden air which is more corrosive than being under water. So, even if the riser is cooled buy milk, it can still corrode from the exhaust passage into the cooling jacket.

 

[Dave S]

Ok........now I understand Frank.

Dave

 

[Sublimetime]

The Bigger issue here is the valve overlap at idle causing the negative pressure pulse. Their "proprietary" addresses this in the riser itself. Raw water still enters and exits the risers.