How Hot Should a Motor Run

[kyngfish]

I bought a second hand boat and when I took it out yesterday I noticed that at times the motor might be running hot.

When we were trolling at 8 to 10kms the temp gauge slowly went to just over half but then when I drove it at up to 30ks it went back down to under half. Then when I was in a 4 knot zone and it was not on the plane it went to just under 3/4 on the temp gaige.

Also when I was flushing the motor the outflow was quite hot but seemed a reasonable flow.

The motor is a Mercury 140 V6. I havn't had this brand of motor before so not sure if this is normal or signs the water pump is on its way out.

Thanks.

[Guest Aussie007]

ask huey he knows all about the mercurys it could be something as simple as the thermostat or it might not even be anything

[SargeRX8]

I don't know much about the cooling system in the boat but if it can relate to a car then it might be right. When driving my car at normal speeds in traffic the car gets a little hotter but when driving on open roads, at speed, the faster movement of air through the radiator helps to cool the engine a little more. I assume the faster you go in the boat, the more water you pump, the cooler it gets.

When my motor is done on its run and we flush it, the water that comes through the nozzles is also hot. Think about it. The engine was running, there is still salt water in the water galleries which is now being pushed out by the fresh water. Also the heat from the engine and metal components will be transferred to the water as it passes around the engine. As long as you don't hear a buzzer or a red light switch on, I think its within operating range. Check the manual online.

[a boat]

Hi, your V6 Mercury is designed to run hotter at low RPM and that is the job of the thermos and pressure valve. If the thermos are stuck open or the pressure valve is faulty the engine runs cold at idle and low speeds -that is not good for many reasons. Once working hard the engine produces enough temp for the themro to be permantely open and you will run coller at high RPM. Temp gauges are at best just an indication and since you have just bought this engine it might pay to get a water pump service including servicing the thermos and pressure valve as preventative maitenance. Then you can start your own service routine Very solid engine your 140HP, just not the best on fuel economy being a carby engine and not the best on emissions, but if that was my engine I would make sure the water pump and above has been done, run XD-100 and make sure she is propped right to see around 5500RPM at WOT.

Cheers,

Huey.

[kyngfish]

Thanks guys.

Special thanks to Huey. I will ask a dumb question is XD - 100 the engine oil, if so why this oil as the manual states TC W3 and I just bought some premium Quicksilver (brand Merc recommend).

It got to over 60 kms at just on 5500RPMs. It has a Solas prop so does that sound OK.

[a boat]

Hi, all oil is meant to met a basic level, that being TC-W3. Mercury make fine oil but the min if you want to stick with Quicksilver would be premium PLUS in that V6. XD-100 is the best oil in terms of lubricating qualities, clean burning and more but it will also cost a little more than say that premium oil.

That is good RPM for that engine if that was with your normal load.

Cheers,

Huey.