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Thread: yamaha 421

  1. #1
    Join Date
    Jul 2010

    Question yamaha 421

    Purchased this unit from you for a customer. Took a while to get it but it finally arrived and I installed it. It tested ok. So I called the customer, gave him the break in card. He went to the lake to put some hours on it becaus he has a tournament this weekend. He brought it back because at idle speeds it gives him a overheating alarm and his water presure guage shows very little presure...2 to 4 pounds. Once on plane the presure gauge goes to 12-15 pounds and the alarm stops.

    I pulled the unit and inspected everything. all looks good, impeller, alignment, intake screens, everything. Any ideas?

  2. #2
    Join Date
    Nov 2006


    If everything looks good with the water pump, then I wouldn't have any other ideas. I would suspect it would have to be something with the water pump though. You might be best off calling the warranty department with your serial number.

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Sterndrive Engineering, Inc. (SEI) manufactures a stern drive designed to replace Mercury Marine's MerCruiserŽ Alpha OneŽ, R, MR, Gen II and Bravo OneŽ stern drives. MerCruiserŽ Alpha One, R, MR, Gen II and Bravo OneŽ are trademarks of the Brunswick Corporation. SEI has no affiliation with the Brunswick Corporation. Consequently, any warranties governing products and or sold by Brunswick Corporation will not apply to products manufactured and or sold by SEI, or to products damaged due to the operation of an SEI product.