Over heating

:?:My outboard is a 2005 mercury 150. It appears to be overheating. The pisser shoots water but steam is coming out too. The water is scalding hot. Will replacing the thermostats help? I am going to change the impeller also.:?:

 

How hot is the water in degrees?

 

Check those items first, but it can be other things too. If it's a saltwater motor the water passages can become plugged with corrosion.

 

Overheating

Even though you have water circulating one thing thats not normal is steam out the pisser. Pressure is important in outboards, will indicate you if you have obstruction. IMO what i would do first since its cheap and always good to do yearly is replace the impeller, give a good visual inspection of the housing also. Any crack or deformity replace it also. If your at it and have never replaced the thermostat do so it won't hurt and also may be the culprit. Outboards are pretty much straight forward when it comes to cooling not many things go wrong in that area.

If you have been boating in shallow water make sure that there is no sand or debris in the water intake.

 

Good advice above. It is possible for the impellor to be damaged from silt and debris without the prop showing damage. Deep silt or very soft sand can do this, even bits of weed. Even a new impellor can be damaged this way. Check the old one, you may well find a missing vane or cracked vane roots. Sometimes odd things like spiders make a 'home' in the outlet passageway for the water. A gentle poke with a soft rod such as strimmer line can help remove any obstruction! Best done with the engine running on muffs.

The steam suggest perhaps a broken outlet hose or connection? The engine should be giving a beeping, warning of an issue, as there is a coolant temperaure sensor in the head on most motors these days.

 

"Appears" to be overheating ? What does the temp gauge say ? Any alarm sounding ?

 

On the bright side of it - you are in good company: http://www.boatdesign.net/forums/bo...-ships-breaking-down-due-gulf-heat-55871.html