Overheated - Riser gasket question

Had an overheat issue yesterday, and after checking the impeller (was fine, changed it anyway), all fluids, etc I started the fake a lake and noticed dripping on the starboard side where the two nylon(?) exhaust manifold coolant elbows are. The front one is considerably more than the rear one. I will replace those, my question is should I go ahead and replace the manifold gaskets as well?

How big of a job is this for a regular joe, and any guidance or tips? Does anyone know the part numbers/equivalent of the gaskets for the exhaust risers?

As to the cause...if anyone has any theories let me have them, but the boat is 10 years old and we run almost exclusively in brackish water. We flush everytime, but in my experience I've seen that Father Time and salt always win, so may just be time to replace some parts.

If you that far, you may want to check the condition of the exhaust manifolds themselves.

Attachment 28539

Gasket is non existent! Will order the gasket kit from skidim. Now just have to figure out why it got hot in the first place.

Thermostat? How do I check that?

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Originally Posted by TL7

Attachment 28539

Gasket is non existent! Will order the gasket kit from skidim. Now just have to figure out why it got hot in the first place.

Thermostat? How do I check that?

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Forget testing the thermostat, it’s not worth the hassle. It’s sounds like you need a new one. They are relative cheap and easy to install. I’d try that before you diagnose it further.

Thermostat opened when I did the boil test. Actually opened shortly after 160*, so I am ruling that out. Will replace anyway since gasket is trashed.

I had quite a bit of rust in the exhaust manifold crossover hose (the one that has a garden hose connection you can use to winterize). Flushed it out. Going to replace the exhaust manifold and the riser, because 2 of the 4 bolts that connect riser to manifold are rusted and in such a hard place to get a tool on to begin with. The gasket in between the two is toast so since I cannot replace it (or the elbow on that end cannot be replaced without separating the riser and manifold) I will just change out both (cha-ching).

I still have no idea why it was getting hot to begin with. Possibly restricted flow due to the rust in the lines but I would have thought that would have caused overheating right away. We were on the water a good hour or so before temp started to rise. We did quite a bit of idling/putting around, boarded twice, no issues. When I really opened the throttle an hour or so into the trip is when this happened.

I wouldn't think a little rust would cause it to overheat. I know there’s been some posts on here about possible blocks in the block but I think those are really uncommon. I’d start at the impeller housing and work my way up for issues. Maybe pull the block plugs and shoot compressed air into the hose after the thermostat and see if you get air flow on both sides. Are you sure nothing was stuck in the water intake line or were you in shallow water?

How old is the fuel? Old fuel will be more prone to detonation under Load. This can cause a series of bad things, overheating could be one of those.
Other than the Engine water temp gauge reading, any other signs of overheating?
I’ve had corrosion build up on sending units that caused inaccurate/erratic gauge readings.

Fuel was definitely old. Due to a knee replacement we only used the boat once last year. So the gas sat for at least 7+ months. The first trip this year it ran really rough, I assumed due to moisture in the water from ethanol. You may be on to something, because this trip we were down to the last of that tank so maybe that is a contributor to the issue. I did put a can of sea foam in it after the first trip where it ran so rough. The second trip it ran better, but still missed now and then. The 3rd and 4th trips (this latest being the 4th) it ran normal right up until it overheated.