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  1. #1

    How-To $30 dollar 160F Thermostat Install

    Update 7/24/2009 Consolidated Information from the Posts

    Tested with 5 hours of riding today in 94 air and 84 water. Worked like a champ. I had lost about 100-150rpm from riding a couple weeks ago in about the same heat. This time riding the heat didn't seem to phase me so thermostat must be doing its job.

    This takes about 4 hours to install and requires 2 days prior a riding day so the glue can fully cure.

    * 160F Sierra Mercruiser Thermostat 18-3555, updated link by brad952
    Updated links by Gus13letter pics at post 70
    Thermostat part numbers are:
    Mercruiser (OEM # to cross reference to another replacement) - 99155A1
    Mallory - 9-43001
    Sierra - 18-3555

    * Solder Gun (Weller SP23L) with flat tip attachement
    * 6inch extension for your torx bit
    * Torx bit for thermostat bolts (not sure the size)
    * JB Weld
    * 3 x 14/32mm worm clamp
    * Tape
    * Screw Driver for leverage about 6 inches long
    * Oetiker clamp or needle nose pliers to remove stock oetiker clamps
    * Right-Stuff silicone

    Step 1 (Remove thermostat)
    Basically go by Riva's instructions and remove the thermostat
    I used a 6 inch extension on my 1/4 socket wrench for all of the bolts.
    The hardest part is removing the bottom 3 bolts. When it was loose enough I used a glove on my left hand to turn the 6 inch extension without it connected to the wrench and with my right hand I would hold the bit up to the screw. I did all of the bolts while standing on the side of the ski and not mounted in the foot wells.
    Step 2 (Remove nipple)
    Using a Solder gun with the flat tip attachment melt off all the tabs. See picture "melt tabs". See picture solder gun to see the tool I used, which is a Weller SP23L with flat tip attachment. You can get this at home depot/Lowes/Ace Hardware. Once the tabs are melted off use a thin blade knife or a razor blade knife and slide it between the gap of the nipple and tabs to make sure you have them melted all the way. Then use any screw driver around 6 inches length and slide it into the nipple. While holding the nipple and screw driver try rocking the nipple out. Do it in a circular motion and be patient it will eventually pop out with medium force.
    Removal Method #2
    by jaffabas
    all you have to do is poor boiling water over the thermostat while still on motor then quickly removed with glove on other hand. (plastic softens and expands with heat) then when you put new thermostat in put a pipe clamp directly over where the tabs go through plastic locking them back on in case they stretched. it took no time and has lasted over 50 hrs racing so far
    Removal Method #3 by wolf513 pics at post 53
    1. Drained the coolant
    2. Removed engine cowling
    3. Removed air intake to the supercharger
    (This took the longest - the stage 1 intake is a PITA!)
    4. Covered the open supercharger intake with a plastic bag and electrical tape
    5. Dumped about a gallon or so of boiling water on the thermostat one cup at a time so I didn't splatter water all over the engine.
    6. Slowly worked at it with gloves on and it popped right out. Did not even have to disconnect any hoses.
    7. Swapped out thermostats and placed a clamp over the whole housing unit.
    Total time from coolant drained to everything back together - 1.5 hrs!
    Tested it out on the lake and I got back 100-150rpms! This mod is definitely worth it. The temps here are usually between 95-105+*F in the summer!
    Step 3 (Replace thermostat)
    With the nipple and stock thermostat removed place in the replacement thermostat. I used a Sierra Mercruiser 160F 18-3555. See attached picture "replacement". This is supposed to work for a 4cylinder closed cooling Mercruiser boat and the sizes matches up perfect to the stock. Put the O-ring from the stock thermostat onto the nipple. See attached picture "O-Ring". Then push the nipple back onto the thermostat housing. It should snap in place and you should see where all your melted tabs line up on the side of the housing. If all the melt marks line up then you have it snapped in and centered.
    Step 4 (Secure thermostat)
    I used black Right-Stuff silicone inside the groove on the top of the nipple. See attached photo "seal and tape". I then used plastic epoxy in the tab holes on the side then placed duck tape over it so it would cure in the tab. See attached photo "seal and tape" and "tab epoxy".

    still doing
    I then put plastic epoxy or JB Weld on the top of the nipple for extra security. See attached picture "plastic epoxy". Doing the glueing in this method I will still be able to remove the nipple in the future by using the Solder Gun and melting the epoxy away. This way if the thermostat fails in the future I can still replace it.
    Step 5 (Install Thermostat housing)
    Use the steps from the Riva instructions and tips from Step 1 to reinstall thermostat. I used 11/25mm worm clamps to replace the stock oetiker ones. I also put 1 gallon of distilled water and 1 gallon of distilled white vinegar into my coolant bottle. Then ran it until the engine warmed up. I drained it and then ran a couple gallons of distilled water to rinse it out. This will clean out your cooling lines before you replace your coolant.

    It's possible if the epoxy isn't correct the top can blow due to the housing flexing during high temps. JB Weld is stronger and you can use it on the top with a stainless clamp or just go ahead and use JB weld on the inside and have a more permanent solution.

    Other methods
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    Last edited by Kinchyle; 07-24-2009 at 11:38 AM.

  2. #2
    suck my wake's Avatar
    Join Date
    Apr 2006
    Sugar Grove IL
    Nice job! I know I gave you s**t before about this but looks like you did your home work. I am inpressed,I hope it works out for you

  3. #3
    Kinch, is this a one time therm replacement job? or can this be disassembled again?...PR

    BTW -Good Job, hope it works out for ya!...

  4. #4
    Quote Originally Posted by Pale Rider
    Kinch, is this a one time therm replacement job? or can this be disassembled again?...PR
    It can be disassembled again. Look at my picture "plastic epoxy" and "seal and tape". In order to disassemble you will need to use the solder stick and melt the epoxy away in the tabs. Epoxy can't stay together with temperatures greater than 550F and starts to crumble. A solder stick will get over 800F so cuts through it almost like butter. The top edge has right stuff around it then a layer of plastic epoxy for that 1-2 punch. To undo this you will need to melt the plastic epoxy around the rim and then use a knife to lift up the "right stuff" silicone. I used the "right stuff" so you won't damage the housing when you melt away the plastic epoxy. It will probably take a little work but it's possible and won't damage the housing. Once the thermostat is replaced just reaply the plastic epoxy. You probably don't even need to plastic epoxy the top. The plastic epoxy on the tabs would be enough because the nipple snaps in place. I just epoxyied the top for extra security.
    Last edited by Kinchyle; 07-01-2006 at 10:40 PM.

  5. #5
    INDY27's Avatar
    Join Date
    May 2005
    Montgomery, Al
    Great job! That should hold up with no problems.

  6. #6
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    League City, Texas
    excellent write up and modification

  7. #7
    JFizzleJR's Avatar
    Join Date
    Aug 2005
    This was linked to in another thread so I'll ttt b/c it's interesting and I didn't know about it before

  8. #8
    Dr Len's Avatar
    Join Date
    Jan 2006
    New Jersey Attitude Capital of the World
    What No JB Weld involved LOL

  9. #9
    skip785's Avatar
    Join Date
    May 2007


    great mod a bit cheaper than rotax

  10. #10
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    League City, Texas
    I think I may have to do this mod.

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