Mercury 9.9 Help

I recently purchased a 1995 Mercury 9.9 outboard. I had it out today and the water pump is working sporadically. Sometimes it works and sometimes not. When it is working, it has a good stream of water coming out. Is this just the bad impeller that needs to be replaced? AND why would it work sporadically if this is the case? Is this replacement easy? Thanks Jake

Re: Mercury 9.9 Help

yes replace the impeller and the thermostat too

Re: Mercury 9.9 Help

Not necessarily. The telltale on these motors is on the discharge side of the thermostat, and flow will vary with the opening/closing cycles of the thermostat.

You can tell if there's enough cooling water flowing thru the motor by comparing the difference in temps between the engine block, and the exhaust side covers. The side covers should be fairly cool to the touch or lukewarm at best. The block will be noticeably warmer although should not be uncomfortable to hold your hand on.

If the exhaust manifold cover ever feels hot, that's way too warm.

That being said, on a motor new to you it's never a bad idea to change the impeller, since there's no way to know when it was last serviced.

If there is any sign of insufficient cooling it's probably a good idea to replace the thermostat, too. Cheap insurance.

You can find a parts diagram for your motor here:

http://www.mercruiserparts.com/SelectModelType3.asp?class_id=2

HTH.......ed

Re: Mercury 9.9 Help

Thanks guys, I was not thinking about the thermostat at this point, but given the fact that, when it was pumping, there was a good steady stream of water and todays 50* water temp, that probably explains it. Im still gonna replace both as a safety net, as you said, I don't know when this was serviced last. Thanks again, Jake

Re: Mercury 9.9 Help

I had a 15 HP Mercury that would do that even when it was brand new,but never experienced overheating problems. But with that motor being a 1995 and you are not sure when the water pump was last serviced,change that thing just in case anyway. Do the thermostat,too. Mine would work like that when you first ran it,but after running ahwile,the discharge stream would run steady and constant after the motor had warmed up. I was told that it was the thermostat cycling between open/close until the motor had warmed up.