496 overheating - not impeller
 

Last weekend my engine started overheating. Sea strainer is full of water and swirling. Exhaust temps are normal, verified on scanner. I found the cap came off the thermostat, so the pin was unable to open the thermostat. Just replaced with a new one. Same problem, slowly overheats. It took a good 15 minutes and it started hitting 180 degrees (normal is always 150). No water in oil. No bubbles or pressure in coolant tank. Circulating pump is not dripping. Is it possible for the circulating pump impeller to fail? Or??

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Collapsed hose in transom assembly??

Either rubber end gaskets on heat exchanger or oil cooler has debris in it.

Raw water flow does not seem to be the issue, the strainer is full of water and swirling and exhaust water output and manifold temps are normal. I inspected the heat exchanger. It was clear and I flushed it. The HE end caps are new and so are the o-ring gaskets. Dexcool 50/50 is basically new and not discolored.

what temp is the stat and where did it come from?

Do a search, this is discussed ALL the time on here.

It's likely that you need to remove your heat exchanger end caps, clean the tubes, and replace the end gaskets as they deform.
And/also, if your antifreeze is not fairly bright pink, has darkened to a metallic color, it needs to be replaced. It's only good for about 7 years or so.

+Are you getting any water in the bilge while running? If so, your air drain actuator springs are worn out. The actuator can be replaced. There is some good info on YouTube about all of this too.

I seem to remember a post awhile back that the impeller came off a 496 pump???

If that was the case, I think you would over heat in less than 15 minutes.

Thanks guys! Well, brand new replacement thermostat and the top piece came off the first time out! Thanks Hardin Marine!

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