Temperature:

[seawings]

I have a 2005 Mercury 150 Saltwater engine. I recently moved the boat from salt water to fresh lake water. I have alway noticed that my water temperature ran on the high side...and no change moving to fresh water. It idles at about 175 degrees and then while underway (less than five mph) the temp. increases to nearly 220 degrees. Once clear of the cove and I increase speed the temp will drop back down to around 200 and stay there until I throttle down again and it goes up. Water temp was 87 degrees the other day. I do have a good stream of water coming out the water exhaust. Any ideas or comments?

 

[gss036]

Re: Temperature:

Check your thermostats. They should be 143 degrees normally, but sounds like they may have a lot of salt build up. At 240 degrees you should be getting an overheat alarm, you are very close to the level.
When the temperature drops back, that is an indication that the poppet valve is opening allowing excess water to exit the block through the exhaust syatem.

 

[Barnacle_Bill]

Re: Temperature:

Corroded thermostats is the first thing that popped into my mind too.