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Changing impeller

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carlnap

Contributing Member
I changed the impeller on my 0

I changed the impeller on my 03 5.0 mercruiser bravo 3 last season. The water pump on this engine is actually in the engine not the outdrive. I was told these are more durable and you can change them once ever 3-5 years. Do you agree??
 
"carl;
You are referring to t

"carl;
You are referring to the belt driven raw water pump low on the starboard front side of the engine, right?
They use the same type of rubberized flex impeller as the Alpha drive leg style pump. My rule of thumb for any of them is replace every 5 years or 200 hours max, or anytime the leg is off or apart; though they can die much faster than that, particularly if run dry, or in sandy, shallow, or dirty water.

If in doubt I do a flow test into a bucket at 1000 RPM. This will quickly indicate raw water pump health.

Just my opinion.
Rod"
 
"a lot depends on where you bo

"a lot depends on where you boat. whether you pick up a lot of silt/sand/mud/etc.

I hear differently, these pumps need to be changed more often. I think it makes sense since these pumps would be run dry more because the pump is so far away from the water intake. especially if you start on the muffs on a regular basis."
 
"I've heard of on-the-engi

"I've heard of on-the-engine raw water pump impellers still working after 20 plus years, but I change mine every 5 years or so.

Jeff"
 
I have a 2003 5.0 MPI that I b

I have a 2003 5.0 MPI that I bought in Feb 2006 with 103 hours. Impeller failed at 150 hours in July of 2006. Still on the replacement at 300 hours.
 
"Jeff;
Mighty good idea I&#39

"Jeff;
Mighty good idea I'd say, and darn cheap insurance.

w2f; Belt driven pumps are mounted below engine crank centerline, and as such in most installations it will be below the boat's waterline.

This means with the boat in the water the pump suction is flooded at engine startup, and the water does not need to be sucked up hill. It's done this way on purpose. Dry starts are minimal.

With a hull pickup the suction plumbing is very short and direct typically. With a Bravo leg pickup of course the routing is more convoluted and the pump has to work harder, as you say. Dry startups are more common in this case.

Alphas are the best setup, since the pump is well under water, and the water is right at the impeller at startup. A dry start up is near impossible. Except of course with muffs, and if you forget to turn the water on!

Rod"
 
"Rod,
I think that is what I

"Rod,
I think that is what I was getting at. Trailer boat vs wet slipped there may be a difference. I trailer my boat. Generally I will run the motor in the driveway on the muffs at the beginining of the season and when working on oil changes etc. Also if it has been a while since I have used it I will start and run to make sure everything looks good."
 
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