Very hot water and white smoke from exhaust port.

[smethvin]

I have a 2006 150 mercury optimax. Noticed last time out that when coming down off of a plane that a lot of smoke came from the exhaust port on back of motor. Came home and changed impeller and gaskets (the gaskets were bad) and both thermostats. Never had an alarm or slow down for guardian mode but still has a but of smoke and very hot water coming from the exhaust port. Seems to be running fine otherwise. Is this hot water and smoke normal.

 

[Chris1956]

The water would normally be about 140*F if the cooling system is working. You might like to inspect the poppit valve.

 

[smethvin]

MY boat did not come with a thermostat so do you mean the water that is coming from the exhaust valve it is like turning on a hot water faucet. I also thought the poppet valve was for higher rpms. It runs fine faster speeds and does not smoke till after slow down and idle and the telltale water is not hot. Just fixing to go on vacation and started smoking. Like I said a little less after changing gaskets and impeller but still worried it could be something else. Will check poppet valve too though.

 

[bilge rat jim]

MY boat did not come with a thermostat so do you mean the water that is coming from the exhaust valve it is like turning on a hot water faucet. I also thought the poppet valve was for higher rpms. It runs fine faster speeds and does not smoke till after slow down and idle and the telltale water is not hot. Just fixing to go on vacation and started smoking. Like I said a little less after changing gaskets and impeller but still worried it could be something else. Will check poppet valve too though.

Actually, your outboard has 2 thermostats- located behind the t-stat covers on the top of the cylinder heads.

 

[smethvin]

Yes we changed those. I meant a temperature gauge. Sorry. I am only worried at this point if the water and minimum smoke coming from exhaust vent below telltale is normal. Never paid attention until last time out when it smoked so bad after slow down and at idle. After replaced stats and impeller kit not as bad but still some coming out.

 

[bilge rat jim]

So, is this smoke or steam?

 

[smethvin]

The water is hot probably steam. Just never noticed till there was so much. Now is it minor. Should the water be that hot to cause the steam. Telltale is normal and running fine.

 

[bilge rat jim]

OK, that sounds like lack of water pressure at low rpms- and you've repaired that problem by repairing the water pump. A couple of suggestions- service your water pump every 2 years, and a water pressure gauge is a nice option.

 

[smethvin]

Thank you

 

[Texasmark]

I think 143F is the standard opening temp for Merc stats. Is on the ones I've seen and mine. 140F is the temperature of a US domestic hot water heater (in the home) when set to the N (normal) position for a "how hot is that" reference. On my engine 2500 rpms is about where water pressure forces the poppet off it's seat and allows bypass water through the block which can be cooler than it was when stat controlled at the lower engine speeds. Steam says something is wrong.

Your OT sensor is probably 195F like mine. If your block temp gets to that temp it will close the switch, grounding one side of your warning horn which is either in your control box or in the wiring harness adjacent. Some boats, like ProCraft for one also have an indicator light that illuminates when the horn is on in the event you couldn't hear the horn as a safety measure.

Steam is not good, unless it's winter and then it's water vapor, not steam and usually normal.

Mark