mercruiser waterpump test

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  #1  
Old 07-18-12, 05:24 PM
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mercruiser waterpump test

hi its jim i have a 78 mercruiser inboard outboard i started it today about 30 seconds running i heard a noise in the outdrive and now i get no water coming out the noise came from the area of the water pump how can i make sure it is the water pump and if it is which one would i need thanks
 
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  #2  
Old 07-19-12, 04:48 AM
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The water pump is located inside the drive on the same shaft that ultimately turns the prop. The bump you heard could be the u-joint or gear failing at the top of the drive. Start it and immediately put it in gear. (Don't run it for more than 15 seconds if it's not pumping water.) Does the prop turn?

Running it without water for more than 15 seconds will toast the impeller, so it's probably shot. It should be replaced every two or three years anyway. Because you'll have to pull the drive to replace it you can give the drive a once-over while you have it off the boat.
 
  #3  
Old 07-19-12, 05:54 PM
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hi rick its jim i did start the boat and put it in drive the prop did engage forward and reverse no water was pumpin out so if it goes in gear does that mean the pump is bad
 
  #4  
Old 07-20-12, 04:56 AM
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Pull the hose that feeds water to the engine. If water is flowing there the fresh water pump is working. If it isn't you either have a clogged intake or a bad pump. A bad thermostat (stuck closed) shouldn't be the problem because there's a bypass on it that allows water to pass to the exhaust. Still, it won't hurt to pull it.

There are two types of pumps you may have on that boat. One is inside the outdrive, which is the most common. If yours is inside the outdrive you'll have to pull the drive and take it apart to inspect it. Mercruiser makes a special socket that you'll need to take the drive apart after you've removed it from the boat.

The other type of pump is attached to the engine and powered by a belt. It pulls water from a through-hull fitting. There is a ball valve on the through-hull. If the lever is straight up the valve is open. It's easier to pull this pump and take it apart. Make sure you mark which hose goes to which port.

Regardless which one you have, if you can't remember the last time you replaced the impeller it's probably shot.

The engine's water pump may also have failed, but that's usually easy to see. If the pulley isn't spinning, if the pulley feels loose, or if it's leaking the pump needs to be replaced.
 

Last edited by Rick Johnston; 07-20-12 at 05:18 AM.
  #5  
Old 07-20-12, 01:13 PM
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hi rick its jim if i take this apart do i replace the whole unit or just replace the propeller
 
  #6  
Old 07-21-12, 02:31 PM
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Im tryin to put the lower half on a 78inboard oitboard mercruiser im havin a hell of a time tryin to get the water inlet to seat all the way in i can get it three quarter way amd ot stops can someone teach me a trick to linein all this up
 
  #7  
Old 07-22-12, 06:27 AM
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If the pump isn't warped when you inspect the upper and lower pieces replace only the impeller. (But it sounds like you already answered that question.) My aging memory says the drive has to be in forward gear to put it back together.

BTW, did the impeller look like it was damaged?
 
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