2011 Mercruiser 4.3L TKS high temp @ low rpm

[Labman047]

Troubleshooting for temperature alarm at low rpm( like idle or pulling away in no wake zone). Replaced thermostat,impeller,sender and receiver sensors at thermostat, and just yesterday the exhaust manifolds and risers. The manifolds were internally rusty. After manifold/ risers installed I had poor water flow to the risers and manifolds. I found this by pulling hoses off of them and was getting exhaust not water. my last steps were to tighten plugs in new risers/ manifolds as well as check thermostat housing and hoses—-after tightening down thermostat tried engine again( on ear muffs). Engine ran great for 20 minutes-temperature around 160 and water flowing great everywhere. Decided to turn it off and restart a few minutes later. Temp alarm (170 deg)and water seems sluggish—hoses are squishy like not filled with water. The impeller is a couple years old.

 

[Bondo]

The impeller is a couple years old.

Ayuh,...... Welcome Aboard,...... Start with a raw water pump kit, rather than just the impeller, 'n be careful you align it properly,....

 

[Bt Doctur]

verify the water inlet hose at the transom does not have a kink

 

[QBhoy]

I might add a couple of comments.
Firstly I’d ask about the suitability of your muffs ? Have they a good fit ?
I’d also ask if you are sure that it’s actually a temperature alarm ? Although 170 is a little hotter than ideal, I’d suggest that the gauges on the dash can be a little less than dead on accurate, but even at that, I’m not sure that 170 would usually set off your alarm. It might usually be a touch higher than that before that happens perhaps. Also that after a running engine that’s been up to temp, then started shortly after, will usually show a little higher than it was for a wee while, until it gets water through it again properly.
Presumably your gear oil header tank has oil in it and your oil pressure is ok ? Those will also set off an alarm.

 

[Labman047]

I will take all of these comments into consideration and update when I get back to the boat— may be a week. Thank you all!

 

[Labman047]

Update: I removed hoses for incoming raw water, and no major issues found. I did run a tiny snake and back flushed hose through transom( some sand debris found). Ran boat for almost an hour with no problems. I am almost thinking the muffs did not have that great of a seal, plus I did not really run the engine hard to have the impeller pull the water in. Thanks for all the suggestions.