Mercury 25hp 2 stroke pee stream is pretty darn hot!

Discussion in 'Outboard Maintenance' started by Snookdaddy, Jan 27, 2012.

  1. Snookdaddy

    Snookdaddy Well-Known Member

    2001 Mercury 25hp 2 stroke

    Is this normal?  I can hold my hand in the stream, but it is at the upper level of toleration.

    I changed the water pump once and it was peeing, but with a little hesistation.  I pulled the lower unit and notice one of the 6 vanes was bent backward. 

    I installed a new impeller and turned the drive shaft "clockwise" to seat the impeller in the housing.  I installed a new thermostat.

    It is still peeing very hot water and seems to be peeing at 80% capacity when compared to my spare 25 merc's pee stream.

    Is it normal for Merc 25's to pee very hot water?

    Is turning the drive shaft clockwise correct?

    Is there something that I'm missing or should be looking for, other than the water pump and the thermostat?

    ** Here's another one for the book.

    When I first bought the boat and changed the water pump.  I was running some extremely low water and the pee stopped.  I went about 250 - 300 yards and shut the motor down.  I jumped out of the boat to inspect the water intake covers on both sides of the foot for debris.  The bottom was muddy/sandy, so no grass was present.  I thought I picked up a plastic bag or something.

    There was no debris on the plastic intake plates, so I took the plates off to see if something had lodged inside the grates...  Nothing

    Then I inspected the plastic plates and noticed the tiny inlet holes were basically melted shut.  I had only run the motor 1/4 mile looking at the pee stream the entire time because the water was so shallow and when the pee stream stopped, I shut down within 250 yards ( I had to find a place to drop into).

    Has anyone on this forum ever heard of this occuring?

    I've asked my mechanic and he said he's never heard of this before.

    I was praying I didn't fry the motor, but chaged out the inlet plates, installed a new impeller and themostat and checked out the compression to make sure no damage was done.  Compression was/is 120/120psi on both cylinders. 

    I have put about 10 hours on the motor since than with no issues, other than it seems to be peeing hotter than... say my Yamaha 40hp pee stream.

    I know that these Mercs use high volume / low pressure cooling, but really have nothing to judge.

    Any ideas?
  2. Brett

    Brett > PRO STAFF <

    If you can keep your hand in it, that ain't hot.
    Hot is not necessarily a bad thing. Hot equals better efficiency, more horsepower.
    Memory says the typical outboard thermostat opens at about 160° F.
    That's the temp needed to cook beef to for safety. So it better feel hot to the touch!

    Pull the starter cord...whatever direction it rotates is the right one... ;)

    Injection molded parts aren't always cleaned up properly.
    Not unusual for overcasting to occlude openings in the parts.
    Sounds like you got one that slipped past QC.

  3. Snookdaddy

    Snookdaddy Well-Known Member


    I mean the tiny holes in the plastic plates were melted shut.  It was peeing normally on minute and the next no pee at all, just steam.

    The holes melted shut within a 1/4 or 1/3rd of a mile run.

    I think I've thrown the old plates out, but I'll take a picture if I still have them...

    The thermostat Mercury Part# 14586 is supposed to be a 120 degree thermostat, so I run the motor and check the temp. It seems hotter than 120 to 140 degrees.
  4. cutrunner

    cutrunner Cert. Yamaha technician

    Invest in a $20 laser thermometer. If its too hot to hold your hand in, especially as the water is pretty cool this time of year, something is wrong, but im not too familiar with those motors, or i would help. Creek runner should know.
  5. Gramps

    Gramps Living &amp; Dying in 3/4 Time

    The '02 Merc 25 on my Gheenoe had about the same symptoms. Heck come to think of it, that temperature of water would be perfect for instant coffee while on a camping trip... ;D But the motor never game me any problems, temp stayed the same after a new T-stat too.

    FYI - DO NOT, I repeat DO NOT attempt to take the thermostat cover off without thoroughly soaking the bolts with penetrating fluid. Can guess how I know that?
  6. Snookdaddy

    Snookdaddy Well-Known Member

    Instant coffee water temp is right on the money. I already changed the thermostat with no issues and used a light coating of marine grease before reinstalling the bolts.

    Broken bolts are a beech!
  7. Creek Runner

    Creek Runner Well-Known Member

    Snook Daddy, you're looking at it from the wrong angle. You cannot tell anything from the Tell Tell outlet, (Pee Stream). You need to actually see if your motor is running hot This is done with a head temperature reading. As Brett said and even yourself, If the thermo is 120 degree the water needs to be hotter than that to open it, Keep this in mind even when it's open it doesn't just cool the engine back down to below 120. That's just what's required to open it, your operating temp will be higher than that. Put some water on a stove and bring it up to 140-150 degrees and stick your finger in it, it's hot.  Also as Cut Runner said get a laser temp gun, every ones hands are different; I have seen my dad hold is hand on engines that were pushing 200 degrees with no problem were as me let's just say I would be saying some 4 letter words. Laser Temp Gun, Head reading , and then you will be able to tell if you have a problem.

    As for the intake plates, yes I have melted them before. Here is what happens at least in my case. I run through sand/mud often and NO I don't slow down; I speed up usually WOT. So you have plastic running through sand at about 35+ mile per hour causing friction which causes heat, if you run long enough they will begin to melt. Has happened to me/and in the dealership half a dozen times or so.
  8. tacobreath

    tacobreath I Love!

    It must be normal for these Merc 25's cuz I can't put my hand in the stream either and on cool mornings it makes steam rise up Lol but after 100 hours she still runs like a top and no problems. Have heard about this hot Merc stream over the years and it's normal for them.