I thought the ball was to allow water to drain out of the manifold when the engine is not running? So you can completely drain the manifolds and raw water system when winterizing with the pump out on the shraeder valve near the heat exchanger ?Wouldn’t a gummed up ball just not allow water to drain out? Wouldn’t this not cause an issue with water getting to the pump (stbd side) and Heat Exchanger (port side) ?

My next step on Saturday is to remove those ball valves and inspect them, then do what you said if nothing is obvious. Doesn’t sound like the fail much, but hey I am special when it comes to boat problems. 😂

Confusing parts here.

You are referring to the winterizing water drain actuators. Those are not a ball system at all.
They are an air actuated plunger that when you air up the schrader valve, it opens both of the actuators and water drains out for "quick winterization" to extend your boating season.
They CAN fail, to where their spring gets soft, when the boat gets enough water pressure (around 3000 rpm/on plane), it pushes the plunger open and water pours into the bilge.
Are you getting water in your bilge? Most folks rebuild or replace them when they go bad.


Check Ball Valve/Tee:

When you are running on the hose, are you hooking the hose to a flush port on the boat, or running on earmuffs attached to the drive?

What I was referring to with the check ball, is what some manufactures install with their fresh water garden hose flush port, a check ball is in the Tee so that water is forced toward the SWP, and not backwards out the drive. I've seen that spring loaded check ball get gummed up with seaweed/debris, and restrict water flow once a boat anything over mid-throttle.

There have been many water pressure threads on 496s here in the past, and you will find some more info and pics.

check ball and connector question

See the above thread.

What about the cooler end cap gaskets ? Don’t they distort after a while and start to block off the cooler ?
Here’s one of many good threads on it, amongst other things:
496HO code 160 help

I have no flush kit. I pull the outlet hose off the sea strainer that feeds to the water pump inlet, insert a plastic pipe in the hose with a garden hose hookup and clamp it on. (Home made flush kit I use for winterization)

I am referring to the check valves located on either side of the manifolds. Port side runs from Oil Cooler to the Manifold. Stbd side I am not positive of the plumbing. My understanding is it allows water to drain out of the manifold when the engine is not running, instead of being trapped in there and sitting. When the engine is running the water pressure closes the ball valve and forces the water to continue to the Heat exchanger.

Pulled the end caps, Clean as a whistle, Plus pulled the hose off the Fuel cooler and the watched the water. It is visibly less at Higher RPMs compared to the other engine, before it even reaches the heat exchanger.

Turned out to be in fact Bravoitis. House collapsed while I was underway. Typically its a more gradual overheating. Also the garden hose just does not produce enough water pressure under high RPMs even for a few seconds. Ended up putting in two thru-hulls for one for each engine and bypassing the drive water inlet pickups. The marina was backed up a month to properly fix the drive inlet. Thanks for all the help and ideas.