'86 Merc 75hp good water stream with muffs on and NONE when in the lake

[inumbskul]

I have an '86 Mercury 75 hp outboard that I bought last Fall. I had the carbs cleaned as the boat had sat for 2-3 years without being started. I hooked it up to muffs and the engine starts right up and runs smooth as silk. I ran it for 30 minutes at different speeds and had on problems at all....good stream of water from outlet tube. I took it to the lake yesterday, it started right up, idled smooth as a gravy sandwich but no water from the outlet tube. I ran it a good 45 sec then got scared i would damage the engine and shut it down....pulled the boat out of the water and checked the outlet to make sure it wasn't plugged with something...it wasn't. I put it back in the water, started it up....same result. QUESTION: Could I get a stream of water from just the pressure of the hose/muffs and still have a bad water pump?

 

[57crestliner]

Re: '86 Merc 75hp good water stream with muffs on and NONE when in the lake

Yes! Your pump impeller is toast~! Think about it. You pressurized the system with your hose. In the lake, you had no suction from your impeller.

 

[hotrod53]

Re: '86 Merc 75hp good water stream with muffs on and NONE when in the lake

make sure your pee hole isn't clogged, I jam a wire up in mine to clear it. Maybe you have flow and just don't know it.

 

[Laddies]

Re: '86 Merc 75hp good water stream with muffs on and NONE when in the lake

Bad pump

 

[bgc]

Re: '86 Merc 75hp good water stream with muffs on and NONE when in the lake

I change my impellers every other year if I use the motor or not. Once they take a set they wont pump water and a new impeller is cheaper than a new powerhead.