1989 454 (7.4) no water

[CptBacardi]

Hey fellas, I just swapped the impeller and the port engine still isn’t flowing water out the exhaust. The hose going into the impeller housing was running water just fine. Now what? Does this thing have a water pump too? Not sure what to check next?

[km1125]

Was there a key holding the impeller to the shaft? Did you lube the impeller with something?

There is a separate pump that circulates water around the engine, but that has nothing to do with the raw water coming in or going out. Is your strainer plugged up?

[CptBacardi]

Thanks for your reply. I lubed the impeller with dawn dish soap and water and I’ve swapped these impellers many times over the years with no issues. The hose going into the impeller housing was flowing water no problem. Is there another raw water intake going into something else?

[CptBacardi]

Yes there was a key for the impeller. Nothing looked wrong with the impeller or the housing.

[tomschauer]

After replacing impellers or the first spring run after splashing I have to "goose" the throttles a bit to lift the water to the impellers. After that they "prime" at idle without issue.

[CptBacardi]

Hmmmm. I did goose to around 4000 rpm. Kept “bumping” the throttle like a chainsaw or tongs ready to flip a steak, haha. Still isn’t blowing water out the exhaust. What am I missing?

[Viper]

What brand engine are we talking about here? I suspect since there is a key in the impeller, it's not a Merc but perhaps a Crusader?

[g36]

Could you have dislodged the key when reinstalling the new impeller? Maybe remove the housing cover and have someone bump the starter to reassure that the new one is turning.

[CptBacardi]

It is a Mercruiser “Blue Water Inboard” 7.4 liter. Not sure how to upload a picture? The shaft for the impeller is just a shaft with a flat spot on one side that the impeller just fits one way... no “key” or separate parts

[Viper]

Okay, so no key after all. Check and make sure that you didn't accidently swap the hoses and put the intake hose on the pump's discharge side. It's the most common mistake. The ports on the pump housing are stamped "in" and "out" for a standard or counter rotating engine. Short of that, did you change just the impeller or the pump housing and wear plate too? A worn housing and wear plate will decrease the pump's efficiency.