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Thread: Yamaha 115 Jet ?

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    Default Yamaha 115 Jet ?

    I just bought a boat with a 115 Yamaha with jet & prop lower units. The boat came with a 2002 Yamaha jet manual stating----" The F115 4-stroke must use a newly designed water pump housing and cartridge for jet applications. Failure to use the new housing and cartridge will result in engine failure". I assume mine was not a factory jet because it's marked 115 -the jet pump that came with it is Yamaha gray and has a black plastic water pump casing on it. Can anyone explain what to look for? Thanks

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    The water pump housing for use with a Jet should have a small pressure relief hole drilled in it. It is generally located on the side of the housing near where the water tube goes up to the motor. The jet drive creates more pressure which can cause your thermostat to be forced open and the motor won't run at the correct temp. This can cause oil dilution among other problems.
    Casey
    Yamaha Dealer
    Petersburg, AK

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    Thanks Akfish1- So if you go to the Yamaha dealer and order a complete jet pump does it come with the water pump? I'm assuming mine is right it has had 90 hrs or so on the jet pump so if it was the wrong water pump it would have failed by now? Thanks

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    Quote Originally Posted by Akfish1 View Post
    The water pump housing for use with a Jet should have a small pressure relief hole drilled in it. It is generally located on the side of the housing near where the water tube goes up to the motor. The jet drive creates more pressure which can cause your thermostat to be forced open and the motor won't run at the correct temp. This can cause oil dilution among other problems.
    Is this only on Yamaha's...?
    “Nothing worth doing is easy”
    TR

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    Akgramps, This applies to Yamaha Four Strokes at a minimum. I'm a Yamaha only dealer so that is what I've dealt with, and I'm sure we never had to do this with the two strokes. If I had to guess, this may apply to other brand four strokes as well.

    K-Kid, If you came in and asked me for a water pump housing for an F115, you wouldn't get one with a relief hole in it. If you told me it was for a jet, we would probably get you the right one or modify one to work on your motor. The water pump wouldn't fail either way, this relief hole is just to let some of the water pressure off the cooling system. If you can call me tomorrow with fax number, I can probably fax you the instruction sheet for where and what size hole to drill or look for.

    And no, if you order a jet pump it doesn't come in the box from Outboard Jets, it is a Yamaha Part.
    Casey
    Yamaha Dealer
    Petersburg, AK

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    I ran a pump with a relief hole for a while, but worried (about possible lack of cooling water) constantly. how would I ever explain to my Yamaha Mech that I drilled out the factory water pump housing, (on purpose) and fried the engine? The theory just didn't make sense to me. how could the same water pump create more (damaging) pressure/ flow, when ran on the jet vs the prop (same RPMs)
    OBJet stated in their manual that the engine wouldn't reach operating temps... (where I grew up that's what the thermostat was for)
    AK fish I respect your opinion and your explantation is the best I've heard.... However I still can't see were this "increased" flow / pressure is coming from.

    I converted my 2000 F100 to Jet 4 years ago, and have been running an Unmodified pump housing for all but about the first month w/o incident. I think my engine gets as warm as any other.... cowl warm to touch after extended runs, "pee" stream warm to the touch, no oil dillution etc

    My $.02

    KK good luck w/ whichever technigue you select

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    The F115 4-stroke must use a newly designed water pump housing and cartridge for jet applications. Failure to use the new housing and cartridge will result in engine failure".

    On closer review of your post... The OBJet assembly doesn't come w/ a water pump. (If you got one in the mail today it would tell you to remove the water pump from your other (prop) lower unit and install it on the jet assy.) I think that's where the "engine failure" language comes from... they're telling you to install a water pump.

    As far as the modification of the pump housing... go to WWW.outboardjets.com and look around for the template or pattern, if you can't find it there contact their customer service and I'm sure they'll help you out

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    Attachment 59619
    k-Kid, your fax wouldn't answer, so here is the relevant diagram.

    This is the instruction from Outboard Jets for the F115 and F150 water pump housing. In th larger motors it is a pretty small relief hole and may make that big a difference, however there are instructions for it so there must be a reason. I have done some testing with Yamaha on the F70 with a Jet conversion, we had a water pressure guage hooked up so we could see the difference between a stock housing and relieved housing. The stock housing was several PSI over their max spec for the thermostats, so we had to play around with the hole size to get the pressure down. The extra pressure comes from the jet pump which is generating considerably more water pressure than the water pick-ups on a standard lower unit.

    Now you have all the info and you can decide what to do.
    Casey
    Yamaha Dealer
    Petersburg, AK

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