Mercury 50 hp cooling question

I am new to the boating world and would like to know how I can tell that my engine is not overheating. I have heard that putting a sensor and a gauge on it is useless, and will get readings that may seem high but are normal. How do I know that my thermostat is working like it should? I have a manual on the motor, but it does not tell me these answers. the book is pretty old and beat up. it came with boat.

Re: Mercury 50 hp cooling question

When asking questions about your engine you should indicate what year, make and model it is. There about a gazillion 50 HP Mercs. Depending on the year, there are at least two indicators for overheat conditions. 1) the tell tale stream. If the tell tale shows a good stream of water, even at idle, that indicates the water pump is working but is no gurantee that the engine is not overheating. 2) the engine typically has an overheat horn or alarm that beeps steady upon overheat. Look for a tan wire exiting the head. Disconnect that wire and ground the end of it with the key on. The alarm should sound.

Water pressure and temperature gauges are not "useless" instruments but rather very helpful tools on keeping tabs on engine health. If they give abnormally high temp or abnormally low water pressure readings, something is wrong. Without a temp gauge, periodic replacement of the thermostat, bypass valve, and water pump is the only preventive measure one can take to ensure the cooling system is relatively safe.

Re: Mercury 50 hp cooling question

I have a 2001 2 stroke merc 50hp that is doing the overheat at full throttle thing. I've been trying to figure out the problem for about a month now and still no luck. I'm afraid the only thing I have learned is there isn't a simple answer to that question. Overheating alarms can be the result of alot of different things. Just got to start replacing or checking them one at a time till you fix it. I've already replaced the impeller, fuel line, fuel bulb, fuel line connector and fuel filter on my boat. Still alarm sounds. I get good stream thru indicator and when alarm goes off, water in indicator stream is slightly warm but not hot. Engine seems to run just fine even when alarm goes off and I can make alarm stop by just slowing down to idle speed for about 15-30seconds.

Next step for me I guess is to replace the thermostat. After that... not sure what to do but did read about the grommet on the water hose going from the lower unit to the head being a possible problem. I haven't checked that yet and am hoping that isn't the issue since it would be hard for me to do myself.