I was chasing a problem on my 47' excalibur last year. I ran out of fuel whilst at idle (don't ask) and had an immediate overheat on the port engine after refueling. I disassembled the water pumps at the dock to find the impeller shredded. It was odd, because the impeller was just replaced and had never had a cooling problem thus far. I recovered all the big pieces during a backflush and removed the heat exhanger ends and cleaned out only a few very small pieces. If my memory serves me one of the fluid coolers is straight thru and doesn't have a matrix to capture particles. This year I decided to switch to the automatic tensioner system and Hardin pumps (I will add to the old automatic tensioner vs manual tensioner thread thats floating around on here) I want to remove the exhaust manifold ball check valves and route the heat exhanger directly to the bottom of the exhaust manifolds to eliminate that as a failure point. I would also like to remove the air bleed system like someone mentioned doing before. Question is what is the best way to block of the small bypass hoses? Trying to get these engines simplified...that have been great so far. Trying to decide if I want to build to 540's with CNC iron heads out of these lumps. Rinda is a must have with all these damn alarms and sensors.

zemaestro - So while I do not have your system, from the extensive reading and additional research, the check valves should be inline using the 1 1/4" water hose. It would seem you could remove the check/ball valve with a t fitting traditionally used for a pressure relieve valve and then top it with a cap. Found this part out while researching strainers.

I also found a diagram for the air bleed system if you need it I can dig it up. I believe it also lists the push lock fitting along with the size. I would think you could remove those and cap them. Could be wrong and look to others for a definite answer but it's fun to test the new knowledge...

We've got different engines, but boat in similar conditions. I'm dealing with same symptoms.

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Just read the jist here as if you are talking about the inline water hose check valves that are on varies MPI Mercruiser engines - it is wise to leave them in or if they are damaged from however ie: freeze damage, age, overheat, cracked, restricted - it is wise to replace them not take them out of the system.

The short story as to part of the reason they are in there to begin with is because they prevent hot heat soak water in the cooling system from entering back into the cool fuel cell after engine shut down. If the heak soaked water from the engine enters the cool fuel cell from drain back, there could be a vapor lock issue when trying to restart the engine. In mid summer 100 degree + temps in Texas we have seen this issue happen when boaters have removed them. Anyways they are there for a reason.

If I am off base here what you guys are referring to oh well, hopefully someone just learned something and I did not wast all this time typing..

My Alpha does the same thing at idle for a bit. I'll have to try the fitting at the transom.

I'm not saying it isn't possible, but I doubt the fitting/hose collapsing on an Alpha is the problem, based on the fact that an Alpha pushes water through the drive and a Bravo draws water via the raw water pump.