Merc 5.0L Alpha getting hot at Idle

[OMARiverRat]

Hey everybody, hopefully someone can point me in the right direction. Finally got the boat out on the river last weekend, and it ran almost perfectly. Ran it a total of about 51 miles @ cruising speed. Temp gauge read approx 140 degrees the entire time I was under way. At the end of the day I got back to the dock and had to idle for about 10 minutes while other boaters launched. While waiting, I noticed the temp gauge was reading about 190 degrees or so. Got it out of the water as quickly as possible. Once I got home, I put the boat on the muffs to flush the silty river water out of the system. Temperature gauge was still reading very hot..about 180 or so. Kicked the idle up to about 2k, and I could watch the temp gauge go back down to about 140 degrees. Any ideas on what this could be? I'm assuming one of the water pumps, just not sure which one it is. Any help on this would be much appreciated. Thank you all for your time.

 

[Walt T]

Re: Merc 5.0L Alpha getting hot at Idle

Impeller

 

[OMARiverRat]

Re: Merc 5.0L Alpha getting hot at Idle

Walt, thanks for the quick response! $38.00 for a lower unit water pump kit, including gaskets... Going to pick it up today over lunch. Do you think running at 190 degrees could have damaged the motor in any way? Opened the hatch and there was no steam, I did notice a large amount of steam coming out of the transom exhaust. <br /><br />Thanks again.

 

[Walt T]

Re: Merc 5.0L Alpha getting hot at Idle

No, I don't think you damaged anything.

 

[crazy charlie]

Re: Merc 5.0L Alpha getting hot at Idle

I would also check the manifolds and risers if you have drains on them.silt can partially clog any of them and the higher rpms of the motor cooling it down is a sign that it may be clogged.Run the motor on muffs and take out a drain plug while it is running,try the riser first.You may have to bend a coat hanger and push the end in and move it around.If black muck comes out in the stream of water then keep probing and pushing it in further.Try each drain and see what is in there.when you ran at 190 degrees the only damage that you could have done is crystalization of the salt water.Did you say you were running in salt????If not then there is nothing to crystalize.The impeller is a great first step but I would check the risers and manifolds as well.Been there -done that!!!! Charlie