Turns out, I should have replaced this impeller sooner

Coolant temp shot up over 220 fairly suddenly the other day. I was able to bring it back down under 200 by throttling back, so I limped back to the marina (I hadn't got far).

This is about 3 years old, maybe 300 hours... I reckon I need to be looking at annual replacements. Time to start fishing for rubber chunks in my heat exchangers

Did you check the exhaust hose?
I installed a new unused impeller which went that route within a month. Fortunately I had just also installed an exhaust house temp alarm which alerted me before the temp rose.
Well worth the money.

I dunno, if chunks got as far as the exhaust hose, I'm not gonna worry about them. I just don't want them blocking the tubes in the HX's.

Yeah, There are several alarms that I would like to have installed. So far, I don't have any of them I just glance at the coolant temp gauge fairly frequently

I put Borel Manufacturing exhaust temp alarm on our current and last boat. Very simple install and it will warn you of a loss of cooling water way before your engine temp gauge.

although said:

I dunno, if chunks got as far as the exhaust hose, I'm not gonna worry about them. I just don't want them blocking the tubes in the HX's.

Yeah, There are several alarms that I would like to have installed. So far, I don't have any of them I just glance at the coolant temp gauge fairly frequently

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No, he was referring to the hose melting due to the high temp of the exhaust when you loose cooling water flow. It can literally melt the exhaust hose. Check out Borel Mfg, great product. No affiliation.

Sometimes a chewed up cam on the water pump will tear up an impeller like that.

Comodave said:

No, he was referring to the hose melting due to the high temp of the exhaust when you loose cooling water flow. It can literally melt the exhaust hose. Check out Borel Mfg, great product. No affiliation.

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I had a cooling water hose fail. The exhaust hose survived the high temp just fine and is still in use more than 25 years later. What melted was the plastic muffler.

koliver said:

I had a cooling water hose fail. The exhaust hose survived the high temp just fine and is still in use more than 25 years later. What melted was the plastic muffler.

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Yes, that can melt also.

although said:

I dunno, if chunks got as far as the exhaust hose, I'm not gonna worry about them. I just don't want them blocking the tubes in the HX's.

Yeah, There are several alarms that I would like to have installed. So far, I don't have any of them I just glance at the coolant temp gauge fairly frequently

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so you don't understand how things work. That impeller sends water through the coolers and out the exhaust. Water keeps the exhaust from melting your exhaust hose. I made a simple suggestion to check your hose for damage having run dry for a time.

I had an impeller really break up several yrs ago. I hadvvery goid luck usingca shop vac to get pieces out.
First vac from pump housing discharge... the disconnected outlet of Ht Xchr and blew back towards pump... vac from pump again. Repeated a couple times until nothing more came out.

Here's the pile of impeller bits that I pulled out of the oil cooler. I think there's more than one generation of failed impeller here!

Sometimes some of those pieces can go the other way and then after firing the engine they get suck into the new impeller, damaging it.. Take a good look up stream of the pump.

although said:

Here's the pile of impeller bits that I pulled out of the oil cooler. I think there's more than one generation of failed impeller here!

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That's a classic. I once had rookie first mate start the generator with the intake closed. The punishment was to collect all the bits to account for the full impeller, reassembling the puzzle.
And of course, really for my assurance that no impeller bits left behind!
Semper Fi!