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Help! 2006 f250 overheat mystery

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  • #1

    Help! 2006 f250 overheat mystery

    I just bought a 2006 Robalo with a yamaha f250. Motor checked out perfect on pre-purchase inspection: perfect compression (205 across all 6); no error codes, nothing unusual, no exhaust housing corrosion. Under 250 hours - all fresh water use. Sounded perfect... first time in the water - overheat at idle alarm after about 20 mins.- crap. Get the boat to the certified yamaha mechanic - one bank running hotter - can't determine the cause. changed waterpump (the entire kit- housing, etc.), changed thermos (one was stuck open), checked poppit - still overheating. I assume blockage somewhere - they tried back flushing several times - nada. I'm the talk of the shop - for all the wrong reasons.

    appreciate any and all suggestions.

    Is it me, or do these engines require a lot of TLC? In addition to running ring free, checking the exhaust housing for corrosion every two years, worring about VSTs and making oil, not to mention oil pump issue on these engines may require removal of powerhead to repair at some point in the future -- what else do I need to worry about?
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  • #2
    I think you find that Yamaha makes a fine engine , well designed and if maintained properly will last indefinitely. All manufacturers have production runs with defects and quirks. This engine is about 9-10 years old with little running time on the clock. Sometimes when engines setup for long periods bacteria ,corrosion, and rust clogs, can form in the cooling circuit.This you will find with any engine.Check maintenance manual flow diagram circuit and trace flow to where it gets hotter.. Look there .

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    • #3
      Why are you idling so long?

      There is a product called Rydlyme I think.
      made for cleaning heat exchanges, that I have read people have had good luck cleaning mineral scale out of marine motors without tearing them apart.
      Might check it out to see what info you can find on the web about it.


      I have read that these larger motors do have a difference in temp from one side to the other, but you did not say how large of a difference there is.

      Did you se this after installing new stats on both sides?

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      • #4
        Excellent advice nautical, I will have the boys check that.

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        • #5
          99Yam, I'm usually fishing in rough water and I like to keep it running. Agree, one bank can be hotter than other. Unfortunately, this one is triggering the temperature alarm. One other thing I should have mentioned;power head was recently removed and speedy sleeve repair/ oil pump repair was done. I'm thinking raw water pinch?

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          • #6
            Yep, saw this after all new parts installed and back flushed. BTW, good shop ,sells yams only. Been selling and fixing them for years. Certified, updated., etc.

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            • #7
              This sounds like the exhaust stack corrosion issue, I'm doing 2 of them next week, you'll find the engine actually is not overheating, it's the small area that the temp switch sits in in getting hot enough at idle to activate the alarm, the ones that I'm doing it is the starboard head switch,

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              • #8
                I hope it is not exhaust corrosion, but at least I'll know. They may have it figured out by tomorrow. In any case I'll be sure to discuss these things with them. Thanks.

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                • #9
                  If there was exhaust system corrosion they would have noticed it when the power head was removed to install the speedy sleeve on the crank shaft.

                  Did the over temperature at idle problem start before the speedy sleeve was installed or after?

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                  • #10
                    Originally posted by boscoe99 View Post
                    If there was exhaust system corrosion they would have noticed it when the power head was removed to install the speedy sleeve on the crank shaft.

                    Did the over temperature at idle problem start before the speedy sleeve was installed or after?
                    That's a bold statement , it is not always easily seen, and if they looked for it during the repair. I'm doing one tomorrow with pretty much the exact same symptoms ,

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                    • #11
                      Might be a bold statement but I am presuming that a competent Yamaha mechanic would know to inspect the block and the mid-section for corrosion if and when the block is removed. That is the only sure fire way that I know of to verify if the motor has cancer or not.

                      Well, with the block removed it is easy to look down into the exhaust system. Also easy to visually inspect the exhaust system on the block as well. Best way that I know to verify if the motor has exhaust corrosion and, if so, the extent of it.

                      Just removing the lower unit and looking up into the exhaust cavity might not tell the full story.

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                      • #12
                        I specifically asked the certified tech that did the pre purchase ( back in December) to check for exhaust corrosion. The report was negative, but that's how he found the oil pump issue; he saw oil when he dropped the lower. I think I might be ok as the recent work confirmed the results of the earlier look at the exhaust - negative.

                        Here's what's interesting - due to low use and minimal time spent idling, this problem could have been going for a while. My surveyor did not detect on his test run. Former owner says ran perfect - again he barely used it.

                        I'll ask them tomorrow what the water temp readings are - another piece of the puzzle.
                        Last edited by James1234; 06-21-2015, 01:45 PM.

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                        • #13
                          have them make a run as long as it takes to trigger the alarm.
                          compare the ECT degrees with the thermo switch on or off.

                          there is a thin divider plate between the muffler and oil pan. can only be seen if the midsection is disassembled.
                          if it cracks or corrodes.
                          that's the symptom.
                          thermoswicth closed,ECT sensor ok.

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                          • #14
                            On the one that I'm doing the thermo switch would come on at idle only, usually after about 10 minutes, and ECT is anywhere from 140 to 170,

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                            • #15
                              and for the ECT, that's normal.
                              did the temp switch go from off to on ?

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