Wrong impeller size?

[heatherfitzgerald]

Just bought a fixer upper boat '83 omc 3.8 L v6 stern drive. Supposedly the impeller and pump drive shaft had recently been replaced. It was overheating, though, so I unhooked the upper water hose to see if the water was even being pumped up into the engine. Had the lower sitting in a water tank so the pressure from a water hose wouldn't fool me. No water coming out of the hose up top. Disassembled the drive and found the impeller which looks in really good condition. While trying to put the impeller back in, ITS TOO BIG. The impeller diameter is about 4 1/4" and the hole is about 3 1/2". Apparently, the rubber fins had been curled over to fit it in the hole. I'm assuming this is not OK. The impeller should not have to be deformed to fit in the hole, right? That's a question...hopefully not a stupid one.

Thanks,
Billy

 

[Don S]

Re: Wrong impeller size?

The impeller diameter is about 4 1/4" and the hole is about 3 1/2". Apparently, the rubber fins had been curled over to fit it in the hole. I'm assuming this is not OK. The impeller should not have to be deformed to fit in the hole, right?

That's how those pumps work. The volume between the vanes is getting bigger and smaller depending on which side of the offset shaft you look, and is what causes the pump to pump.

Maybe this will help. http://www.johnson-pump.com/jpindustry/impeller_pumps/impeller_generalspx.htm

 

[heatherfitzgerald]

Re: Wrong impeller size?

Thank you for the quick response and for the link showing the pump fins in action. Now the problem is that I have to look for another cause of no water getting pumped up to the engine from below. Like I said, the lower was in a tub with the prop removed for safety and no water was coming out of the water hose up top. Ran it for a couple minutes in gear and the prop shaft was turning. Any guesses? The stern drive model is OMC 983487.

Thanks,
Billy

 

[bruceb58]

Re: Wrong impeller size?

The pumps aren't self priming. You should do your test when the boat is in the water.

By the way, the drive does not have to be in gear for the water pump to operate.

 

[heatherfitzgerald]

Re: Wrong impeller size?

Thanks Bruceb58

Not self priming? Then should I run water with a hose into the motor to fill all the cavities, then see if the impeller is picking up from below? It would be much easier to do all of this guess work at home than at the dock of a lake.

If I put it in a lake would it still not prime itself or is it sitting low enough in water to cover over some of the other holes in the lower drive?

The reason I thought it needed to be in gear for the pump to work was because whenever I have the water hose and earmuffs hooked up to it, water only flows out of the upper hose when it is in gear.

Thanks,
Billy

 

[bruceb58]

Re: Wrong impeller size?

In a lake the water level is above the impeller so it has water in it.

With muffs on, you should see water out the hose going to your thermostat when the engine is running. Does not have to be in gear. The motor would overheat while in neutral if that wasn't true.

 

[Howard Sterndrive]

Re: Wrong impeller size?

whenever I have the water hose and earmuffs hooked up to it, water only flows out of the upper hose when it is in gear.

Thanks,
Billy

I agree with Bruce, that makes no sense.
you'll want to verify that and fix whatever the issue before launching. stripped w/p shaft splines or something maybe.

as far as the lower unit in a pail, here's how deep the pail should be (i.e. not possible for a pail to work)
when it is this deep, the impeller is under water and will self prime

 

[willard887]

Re: Wrong impeller size?

I have the same issue going on right now with mine. It's in the shop right now, new impeller no water. I will find out Monday whats wrong with it then i will post. They seem to think it's an air leak somewhere.

 

[THE BEEF]

Re: Wrong impeller size?

On over heating issues with a stringer, One simple thing to do is give the swivel bearing about 12 shots of grease and see if it stops the problem. you might be sucking exhaust gases instead of water. The grease hole is in the front half way down the drive. you will need a flex hose. If it stops O/H the swivel bearing seals need replaced.

Beef