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  1. #1
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    Please help! 200 hp v6 overheating

    Hello everyone! Hoping for some help with an overheating merc 2.4L. It's an older one, 1982. It has a new water pump and a new "over-temperature" sensor. The over-temp sensor is hooked to a red led in the dash. It comes on if the temp goes beyond a certain range, but I have no idea at what temp the sensor activates as I do not have a temp guage. The part number for the sensor is 97465 and is a mercury part.

    The engine runs great and the light stays off if I'm running 1/2 to 3/4 throttle, but if I go full throttle for about 30 seconds the light comes on. Light goes back off if I back off the throttle for a bit.

    The water pump seems to be working good, strong stream comming out of the pee hole. Also, this model did not use thermostats, it has restrictor washers instead and that is from the factory.

    Engine was just rebuilt with a new piston in #5 and new rings on the rest. Block and heads were cooked out and closely examined, no blockage in any of the water passages.

    Not sure where to go from here? Any help would be greatly appreciated.

  2. #2
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    What is the engine height? An engine jacked up too high will not get enough water. Do you still have a poppet valve in place?
    "One of the penalties for refusing to participate in politics is that you end up being governed by your inferiors". Plato .

  3. #3
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    I will have to check the height and get back to you on that as I am not near the boat right now. Where should I measure from to get the height?

    As for the poppet valve, if that's the one right by cylinder #5, then yes it is still installed. And it is not new. We re-used the old one durring the rebuild because it looked fine. Should I remove it or is there some kind of mod kit for it, or replace it?
    Last edited by Scottko; 05-28-2017 at 07:49 PM.

  4. #4
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    If your tempeture sensor is located in the center of the head it gos off at 240*

  5. #5
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    No 200 mercury ever came with restrictors and a poppet valve. Put thermostats in it.

  6. #6
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    Quote Originally Posted by roadkill636 View Post
    If your tempeture sensor is located in the center of the head it gos off at 240*
    The sensor is located between cylinder #1 and #3 (between the two top cylinders on the starboard side). Thank you! 240* is scarry! I need to get this figured out before something bad happens.

  7. #7
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    Quote Originally Posted by Capt.Insane-o View Post
    No 200 mercury ever came with restrictors and a poppet valve. Put thermostats in it.
    I was going off the marine engine dot com web site. It shows restrictor washers (stainless) for a mercury part. That's what was in the engine on disassembly and it hasn't been apart for over 17 years. However, I have never had an over-temp light on it till this last rebuild. It was rebuilt 17 years ago.

  8. #8
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    Yep. The 240* is between the plugs and 190* is off the side of the head
    Attached Thumbnails Attached Thumbnails 1496026607234180791808.jpg   14960266766751404292976.jpg  

  9. #9
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    Rebuild the poppet valve, put a new bushing in the block and put thermostats in it and start from there. If it has the old style head bolt pattern a good place to look is if a fire ring is leaking on one of the head gaskets and pressurizing the cooling system.

  10. #10
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    Quote Originally Posted by roadkill636 View Post
    Yep. The 240* is between the plugs and 190* is off the side of the head
    Would you happen to know the part #s for those sensors? Maybe I got a 190* where it should have been a 240*?

  11. #11
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    97465 is the 240*

  12. #12
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    Quote Originally Posted by Capt.Insane-o View Post


    Rebuild the poppet valve, put a new bushing in the block and put thermostats in it and start from there. If it has the old style head bolt pattern a good place to look is if a fire ring is leaking on one of the head gaskets and pressurizing the cooling system.
    The head gasket bolt pattern is the top picture you posted. The head gaskets are new and I did get the heads resurfaced (not shaved down, just resurfaced to make sure they were nice and flat). Also, the new gaskets were coated with copper-coat gasket spray.

    I didn't see a bushing in the block? Just the plastic parts and springs and diaphram of the poppet.

  13. #13
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    Quote Originally Posted by roadkill636 View Post
    97465 is the 240*
    OK, thank you for verifying that. Looks like I do have the right sensor.

  14. #14
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    #15 Carrier #16 Grommet


  15. #15
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    Hey Scott what part of MN are you from? What kind of boat is this motor on?
    If I don't ask any questions, I'll never learn anything.

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