25 Mercury 2 Stroke Running temperature

Discussion in 'Outboard Maintenance' started by Jakeellington, Jan 22, 2015.

  1. Jakeellington

    Jakeellington I Love microskiff.com!

    Blew up my 25 Merc 2 stroke not being careful putting around in the marsh. Had a good mechanic rebuild the entire motor top to bottom new water pump as well. I also had him put on an aftermarket temp sensor and alarm.

    After the rebuild during the break in the alarm would go off after a min or so of running half throttle or two mins of putting around. We ran the motor with the mechanic and when the alarm we hit the motor with the Laser Thermometer. The exhaust jacket and everywhere the water jacket covers the cylinders was fine 130 degrees but the very small area at the top of the cylinders (where the temp sensor is) and in the small areas right around the spark plugs ( no water jacket there) was like 230 which is way hot. My question is does anyone know this motor well and know if those areas are designed to run hotter than the rest of the engine? I just want to make sure this engine is not running hot after the rebuild? We are taking the alarm off the motor since we think the motor is fine just the top and the small area around the plugs is designed to run hotter.

    The really hot pee stream on these motors has always had me worried since I have only ran Yamaha in my life and their pee stream is noticeably cooler.

    Any insight would be helpful thanks
  2. HaMm3r

    HaMm3r Well-Known Member

    Don't know about the specific block temperatures, but on my old Merc 25 2 stroke the telltale stream was quite warm, borderline hot at times. On the Tohatsu-made 25 2 stroke I have now it's cool.

  3. Dillusion

    Dillusion devilray snob

    My 25 merc water stream would almost burn the top of your hand when put under it after running room temp water through it from the hose.

    I hit it with the laser thermometer a few times and the water jacket, even by the spark plugs, never hit past 119-122 degrees.

    230 IS way hot.

    Are you running with a thermostat?
  4. gheenoelotide

    gheenoelotide I Love microskiff.com!

    idk about the actual temperature, but mine has run real hot for a long time, no problems at all

    think its just the way they run. my motor has been ridiculously reliable. an old 03' still runs and looks new
  5. bw510

    bw510 I Love microskiff.com!

    The water coming out of these motors is a lot hotter than most motors for what ever reason.
    I was very worried when I bought mine but found its normal .