[McFish]

Hi, Sorry for my ignorance on this one but i have just bought a Trophy 21 ft wa with a merc 150 v6. The engine is starting first time and i had the boat on a trial run last week. The engine was a replacement which a got a dealer to add a few months ago as the previous owner of the boat had blown a piston on the merc 175 which originally came with the boat. The problem i have is that the temperature gauge on the dash is not working, there is a slight jerk of the needle when ignition is switched on, but no further movement when engine is running (for 5 minutes in a barrel at idle). I did re-attach a tan coloured wire running down the right hand side of the engine block, which had been removed or come loose from a connection. Any ideas as to what i can do now. Thanks

[KCLOST]

I guessing that the tan wire would be the overheat switch lead that should go to the terminal block. The switch is located inbetween the top two spark plugs on the starboard (right) side of the engine.The temperature sensor is probably on the other cylinder bank.. And is placed in the exact same location. Look between the top two spark plugs on the port (left) side. That is probably where the temp. sensor is, if you have one. The wire connected to it should go directly to the temp. guage. I think it is tan with a blue stripe...

[McFish]

Thanks KCLOST the wire i had reconnected actually originated on the left side of the engine where you had pointed out that the temp sensor should be. I started the engine again and let the tell tale show and there seems to be some temp registering on the gauge, it is hoovering around the 125-130 mark at idle. When the ignition is turned off the needle jumps up to around 140-145. I have not moved out of idle as i don't have a big enough tank for the engine to run in and it won't run on muffs (no tell tale showing). I did remove the tan wire connection and the gauge immediately dropped to minimum so i am hoping that the problem is solved. My biggest worry now is that someone before me disconnected this temp sensor wire because the engine had a problem overheating. Anyway i will have to wait until i put her in the water this weekend to see for sure. Thanks again for your help.

[KCLOST]

Tell me what you are seeing...Follow the wire that you connected.... What did you connect it to? Was it a brass threaded stud (which would be the temp. sensor)? And on the other side of the block is there another wire that exits the head at the same location? And if so where does it go? (terminal block maybe?).. If that is the case, the first one would be the temp. sensor and the second would be the overheat switch. The switch will sound off the warning alarm if your engine heats up to 240F.On the temp. sensor I would like you to check and make sure that the sensor is fully inserted. I believe on your engine that sensor should touch metal. It is very easy to remove.. So go ahead a remove it, adjust it if necessary so it touches the cylinder head. It is either that, or it just measures the water temp through the cylinder head jacket. You can find this out, by removing the sensor and starting up the engine. If water exits the hole it is obviously measuring water temps. that will be lower than metal.. If no water comes out, that sensor should touch the metal because that is what it designed to do...

[KCLOST]

And your engine should run on the muffs just fine.. If you operate the muffs properly...You may be due for a water pump/impeller replacement. It should be done at least every other year...