How to know if water pump impeller is working?

jvr440

Cadet
Joined
Mar 30, 2005
Messages
27
How does one tell if the water pump impeller in the lower unit is bad? This is a 1981 mercruiser 120. Outboards have the telltale pee hole but I've never heard of how to know if it's working on an I/O.<br /><br />Thanks,<br />Joe
 

blackz3

Petty Officer 2nd Class
Joined
May 17, 2003
Messages
159
Re: How to know if water pump impeller is working?

do you have a temp gauge?
 

lenny2113

Petty Officer 1st Class
Joined
Jul 24, 2002
Messages
376
Re: How to know if water pump impeller is working?

As blackz3 says, high temperature reading would mean that impeller replacement may be needed.<br />If it is older then 2 years old, replace it. If you do not know how old it is, replace it. <br />It is a pretty simple thing to do it yourself. I change mine every year during the winter. This way I know for sure I will not have to worry about it when the season starts. <br />Good luck!
 

Phantom17

Petty Officer 1st Class
Joined
Feb 7, 2005
Messages
343
Re: How to know if water pump impeller is working?

I would say if your over 170 consistantly, replace it. Mine goes up to about 165 170, then cools to 160. Don't let it overheat.....
 

flashback

Captain
Joined
Jun 28, 2002
Messages
3,665
Re: How to know if water pump impeller is working?

Yep, thats about it, until you have it in your hand, you won't know. But high temps are a good indication.. if you run it for 10 mins. and can lay your hand on the exhaust manifold without getting burned, the pump is probably OK... :D
 

jvr440

Cadet
Joined
Mar 30, 2005
Messages
27
Re: How to know if water pump impeller is working?

Thanks guys, I know I could watch the guage but thought there may be some telltale way to know if it's working as soon as I have it running. I just got the boat so don't know how old the impeller is so I suppose I'll just replace it. Is it necessary to get the kit with gaskets and wear plate or is only an impeller usually all thats needed?
 

jlinder

Lieutenant Junior Grade
Joined
Jul 5, 2004
Messages
1,086
Re: How to know if water pump impeller is working?

Mine is pretty simple to change out (OMC cobra). If yours is, just pull and check it out.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: How to know if water pump impeller is working?

Get the gaskets. NEVER reuse old gaskets or you will end up with an overheat problem when the suck air instead of water.<br /><br />And NO it isn't as easy to change as a Cobra.
 

marinemech1

Chief Petty Officer
Joined
Mar 26, 2005
Messages
623
Re: How to know if water pump impeller is working?

remove water in hose to thermostat housing start motor at idle it should have about a 6" head of water
 
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