What is an impeller ? I am planning a trip to lake Powell and I was told to bring an extra impeller. I have a mercruser alpha 1, 454. Any info would be greatly appreciated.


fishpaw

fishpaw,

Your engine has an impeller that is basically an internal, finned water pump. They come in a huge variety of sizes and there's one made specifically for your engine. Make sure you get the right one or it probably won't fit or won't work.

Here's what one looks like...


It would fit snugly into an apparatus like the thing on the left side of this picture...


It's driven by the engine and pumps water through the engine to keep it cool. The fins on the impeller are made of rubber and when they start to wear out they can shred. When that happens, two things happen. The first is that it no longer pushes water and the second is that pieces of the blades that came off can end up moving through the engine's cooling system.

When THAT happens you end up having to track down the pieces. IF the pieces are small they can go as far as the thermostat and prevent it from operating properly.

Don't ask me how I know this, but I will tell you it costs $250.01 to have the impeller changed and all the little pieces traced down and removed.

You also should have a tool kit on board with a set of screwdrives, open end and socket wrenches, so you can handle minor problems like that when they pop up.

Here's a link to an article on how to change the impeller. It answers a lot of questions about the job.

I would add a large wood dowel to your kit so you can plug the sea water hose. This way you can change it out on the water if you have to. Nut Drivers come in handy too.

I believe your Alpha has the impeller in the outdrive?

If you are thinking you would replace an impeller yourself I would recommend a factory service manual.

How old is the current impeller?

If it has some age on it, change it before you go and maybe take a spare?

Spare Alpha impeller won't help you at all on the water. It is indeed in the drive leg where it's wonderfully convenient tpo change, if the boat is out of the water. You cannot change it if the boat is in the water.

Thank you guys for the advice. Ok ya'll where does the impeller live I looked at the book for my boat and I can't find it I didn't see in in the engen comapartment and I am afraid of the out drive.


fishpaw

Fishpaw, here's a blow-up of an Alpha drive lower unit....part #27 is the actual impeller...

Alpha drive impeller blow-up

You'll have to separate the lower unit from the upper housing to get to the impeller. I'd rate it maybe a 3 or 4 beer job at the most!!!

Yup, like T-squared said it's not as scary as it looks.

21' reinell hardtop/ 351w 245 omc outdrive ,,,
Closed cooling system Does it have impellers ?
problem is boat overheats when underway,,,but not ideling at dock...

You'll have better luck if you start a new thread.

That said, I'm sure your boat has an impeller, not sure where it is though. The symptom you describe is more likely an air leak between the water pickup and the water pump, on a part of the drive that's underwater and slow speed but out of the water on plane.

even with closed cooling system ?

Yep. An impeller brings in raw water. In a raw water system, the water goes through the heads and manifolds aided by the engine water pump and thermostat.

In a closed cooling system, there is a heat exchanger between the cooling system and the raw water system. Raw water is still needed to cool everything off as there is no radiator, so the impeller sends raw water water into the heat exchange system.

Even in a closed cooling system, depending on the engine, even the upper part of the exhaust manifolds are hooked to the raw water system as that is how the hot water that went through the heat exchanger leaves the boat.

Those ports on the exhaust manifold are usually blocked off with a raw water cooling system.