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  1. #1
    Cadet
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    Default Changing Water Pump on mercruiser 4.3

    HiWonder if anyone can help on this matter. I've just changed the water pump on my maxum 1900sr the problem i think i have is as follows. When testing the engine on a hose pipe after changing the pump i noticed that water only seems to be exiting the transom on the left hand side as you look at the back of the boat. I am getting exhaust fumes and the odd splashing of water on the right hand side. I'm sure in the past i have seen water exiting via both sides, does this mean i have an air lock in the system or does the water only exit via one side?The engine in question is a mercruiser 4.3 fitted with an alpha one leg.

  2. #2
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    Default Re: Changing Water Pump on mercruiser 4.3

    Also do you know where the thermostats in the exhaust system are located?

  3. #3
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    Default Re: Changing Water Pump on mercruiser 4.3

    There are no thermostats in the exhaust system.Are you operating this thing on level ground while this is occuring?Are you overheating?What is the real complaint?

  4. #4
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    Default Re: Changing Water Pump on mercruiser 4.3

    The boat is on level ground, and its the left hand side of the engine that is getting boiling hot. To the point where you can not hold your hand on the top of the exhaust chamber, where as you can on the right hand side comfortable.My question is has this been caused because an air lock has taken place in the right hand side of the engine?My thoughts now are to drain the system completely of water and to start again....

  5. #5
    Moderator Bondo's Avatar
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    Default Re: Changing Water Pump on mercruiser 4.3

    It's an Open Cooling System.... No such thing as Air-Lock.... Did you change the engine mounted recirculating pump, Or the outdrive mounted waterpump Impeller ?????Due to the design of the cooling system, one side will Always run a little hotter...The Only T-stat is mounted in the T-stat housing on the front center of the intake manifold....
    Any Grease is Better,..... Than No Grease at All.......

  6. #6
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    Default Re: Changing Water Pump on mercruiser 4.3

    Okay i understand how things work now have managed to find a few detailed diagrams and i've got my head round how it all works now. I have proved that by reducing the flow one side of the t-housing the water does then pass through the other side and out the correct side of the transom. I posted the question mainly because i'm sure that in the past the water was evenly ditribtued when exiting either side on the transom. and now its not doing so. You have to reduce flow on one of the pipes to achieve this when on a hose. The boat is on a level drive way so i see no reason for it always past out of the right side.I'd changed the circulating pump on the front of the engine. Reason being the old one had a bearing failer.

  7. #7
    Moderator Bondo's Avatar
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    Default Re: Changing Water Pump on mercruiser 4.3

    Well, in that case, is 1 of your risers restricted ????Have you replaced the Impeller in the last year or two ????A broken, missing impeller vane Could be restricting the flow somewhere.....I'm still not too sure you even Have a problem....
    Any Grease is Better,..... Than No Grease at All.......

  8. #8
    Chief Petty Officer
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    Default Re: Changing Water Pump on mercruiser 4.3


  9. #9
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    Default Re: Changing Water Pump on mercruiser 4.3

    Bondo i've taken the exhaust riser off and there seems to be only a small bit of growth inside the water chamber section, i'd there for say there is nothing restricting the follow of water. I'm planing to take the boat to a local lake after work tomorrow to see if she does over heat. The impellar was replace about a year and a half ago.Just clicked on that link and none of the pictured tstat housing are the same as mine. Thanx for all your input though guys guess i'll report back tomorrow with more info

  10. #10
    Moderator Bondo's Avatar
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    Default Re: Changing Water Pump on mercruiser 4.3

    At a Year + 1/2, You're About Due for another Impeller....
    Any Grease is Better,..... Than No Grease at All.......

  11. #11
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    Default Re: Changing Water Pump on mercruiser 4.3

    whats the score with changing the impeller then is it a leg off job and new gasket sets all round once you've changed it? Is this something i can under take or do i need a dealer to do it?

  12. #12
    Moderator Bondo's Avatar
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    Default Re: Changing Water Pump on mercruiser 4.3

    Go to the top of the page,+ click on Manuals.....Then Buy 1 for your engine/outdrive....It's Not that Bad,+ I know you can do it.....
    Any Grease is Better,..... Than No Grease at All.......

  13. #13
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    Default Re: Changing Water Pump on mercruiser 4.3

    Well i took her out on a local river this evening, had to maintain a very low speed because of restrictions here in the Uk but everything seemed okay, temp gauge was reading about 165 degrees which is what the boat normally runs at. So i guess i was worry about nothing, I will look into changing this impeller though as i don't want to be caught short in the big wide ocean!Thanx again for all your input fella's its much apprecatied

  14. #14
    Petty Officer 1st Class
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    Default Re: Changing Water Pump on mercruiser 4.3

    The impeller is pretty easy to change. The leg casing is split about halfway down. Leave the leg on the boat. Drain the oil (two screws, one on top, one on bottom) and undo the 4 nuts and zinc bolt that hold it together. The bottom half of the leg should drop off easily to expose the pump. When you refill the oil, make sure that you fill it from the bottom up with a pump to prevent oil bubbles. Fill until oil dribbles out of the vent hole but no higher.

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