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Broken Thermostat bolts

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  • Broken Thermostat bolts

    Just for grins I decided to check the thermostats on my 1989 175ETXF. Bad plan. I ended up breaking two of the eight bolts. Then I managed to break an easy out inside of the first broken bolt. All of the bolts had lots of white chalky corrosion. I used a dremmel tool to eat away the broken tap and at least 6 more bits to clear the first bolt hole. Can I tap the housing for the thermostat cover bolt without going into the rest of the block or will it leak there. it's only one hole out of many. Thanks in advance.

  • #2
    Oh the easy outs...bad things they are, wish I knew how many I am after removing after others have broken them off in bolts. Best to get a small drill right down the center of the offending bolts then drill with a bit that is slightly smaller than the tap drill size for said bolt just leaving the bolt threads behind. Then run a tap very carefully down through to clean out the remains of the bolt threads.

    Anyway I don't understand why you need to tap the hole in the thermostat housing if you got the broken bolts out??? Could you explain or provide a picture of what you are up against?


    • #3
      Damn easy outs should be banned from sale.


      • #4
        The bolts holding the thermostat cover go through a non threaded 1/4 inch hole in the head cover before they find threads. In digging the old bolt out I have buggered up those threads on both holes. There appears to be about 18 of those bolts holding the head on. I can tap into the hollow chamber under the cover to hold the thermostat in. It just won't be threaded into the head. Past the head seams to be open space that led to the corrosion from the water passages. Is there any way to flush the metal chips out of the water passages? Please don't suggest pulling the heads and helicoiling the damaged thread area. I don't know how many of the bolts I would break doing this.

        I have at least 5 sets of various easy out sets and have a broken piece in each set. All seem to be made in China. I keep thinking someday I will find a set that works but for small corroded stainless bolts in corroded aluminum is I think impossible. Drilling stainless with a hand drill outside on a mounted outboard I don't wish on my worst enemy. Break a tap off inside the hole you carefully drilled, sucks big time.


        • #5
          No easy way to do it really. Like you said stainless in aluminum is not good once the corrosion starts. I would have shop vac and suck up the swarf as you go. If some bits get in the water passages it will just flush out the exhaust....hopefully.

          A map torch with a fine tip on it and heat the heads of the bolts and smack them with a hammer few times. Heat.. let cool several times before you ever try turning them. You are going to burn some paint off...that's part of it.

          There is a place for easy outs. ..not many though. I some that are made in Germany and they are pretty forgiving. Having good taps is another thing..if you use cheap box store stuff you are asking for trouble.

          Good luck


          • #6
            OK I'm back at this repair. Question, if I put a hose in the thermostat hole where will the water go. I'm sure there are metal shards from my botched broken bolt repair. Can I flush them out some way? Should I run the motor without thermostats. Without thermostats would running water through rabbit ears help flush anything. Again, thanks in advance.


            • #7
              You can certainly put a garden hose/water thru where the thermostat is. The lil pieces will go the same route as if running the engine on muffs or in the water, likely out the exhaust.

              Those small pieces, un-like a torn up impeller, dislodged shouldn't be an issue..

              If you like, you can remove the LU, attach a hose to the water pipe up tp the power head and remove the t stat cover. Then flush water upwards.
              Obviously, make sure water doesn't get into someplace under the hood it doesn't belong..

              What was your final fix BTW?
              1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR


              • #8
                Hey Scott,
                Ended up putting a Helicoil in the first layer of head. Upped to a 1/4 inch short bolt. All lined up and should be good. There is a lot of room passed the shortened bolt which enters the cooling passages. Hope I didn't muck it up. Now dealing with oil injection system. Supply line is leaking everywhere and I hope it will pull through the floor of my 20' Whaler.