Merc 500 Water Pump Issue

[Aqualift]

Re: Merc 500 Water Pump Issue

Nice looking Merc 300.

Damage from freezing is pretty rare in the powerhead. The way the water passages are layed out, they sort of self drain. I wouldn't worry too much yet.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

I downloaded a manual and I am getting ready to begin the process of fixing the gaskets or whatever is wrong. It looks like the cooling gasket is showing some deterioration/corrosion.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

New twist to the story:

I tried the final test - a tight fitting hose on the copper pipe. I still had water leaking back down around the pipe but I also had a very strong flow from the tell tale pipe. (I didn't have that before.)

So now I'm thinking that the water pump may be bad after all. I connected a power drill (via a hose and screw driver .... hey, it worked) to the drive shaft and ran it in a tub of water. I put another hose in the pump outlet and it pumped water.

I'm assuming that the drill is turning at much much lower RPMs than the motor would turn, but if I hold the outlet hose up it will not pump the whole way to the top - should it? It's definitely pumping - but it is definitely weak.

 

[Aqualift]

Re: Merc 500 Water Pump Issue

Good to hear you have a strong flow out of the tell-tale.

If you don't know the history of the motor, odds are it needs a new water pump impeller. They are not very expensive and are easy to replace. Many people put a fresh one in on a yearly basis anyway.

 

[Solomon Shaffer]

Re: Merc 500 Water Pump Issue

Good news - she's pumping water!

I had three issues:

1. There was a blockage somewhere (came free with water balloon)
2. The water pump was slightly worn but not shot (it was weak I guess)
3. I was using a tub of water to test the motor. (Which is why I was getting hot air out of the tell tale tube....$6.00 muffs are a great investment!

Thanks for all your help! She's going for her first run on Raystown.

I'm sure I'll be back..this is an old cheap boat

 

[Iandayen]

Re: Merc 500 Water Pump Issue

Sorry I didn't get a chance to reply.

Are you still getting water out the front of the cowl? If so you have a leak somewhere, the most likely culprits are your water jacket cover (yes the cover around the spark plugs, it is not a head, it is just a water jacket, you can take it off and replace the gasket in about 20 minutes) or your tell tale inlet/outlet from the block to the cowl.

The Impellers on these motors are pretty easy to replace.

I went and bought a whole new housing and impeller with gasket kit, but the bottom part of the housing didn't fit quite right, so now I have a metal bottom housing and a poly top housing, it seems that the housings for these made now are more of a "universal" housing, and the round part with the O-ring sealing off bearings/gear oil are a tad too big, everything else lines up nice though.

once you have the bottom housing off, you can see and easily reach the impeller housing, take off the 4 nuts on top, remove gaskets and clean gasket surfaces, replace impeller (spinning the shaft clockwise as you look down from the top while you replace the top housing) and gaskets and you are good. Now that I know how to do it, it should only take me about 30 minutes of work to take the lower unit off, replace the impeller/gaskets and then put it back together and get her going again.

I would highly suggest replacing the impeller, especially if you don't know when it was done last, an impeller kit and gaskets from this site are like $20 - well worth the money to keep your motor from going to the dumps.