View Full Version : Replaced impeller did SUM-FIN wrong

06-26-2012, 10:28 AM
I replaced the impeller in my M/C 1985 S/S. Now it's not cooling. It seems this can only go in one way. Any comments on what the heck I did wrong?


06-26-2012, 10:33 AM
Did you put the housing on upside down? If so, it will just push water out instead of suck it in.

If that's the case, go flip it around and write with a paint pen in big letters "TOP" when you get it straightened out. That impeller housing can be bolted back together upside down. This is a common mistake. Also make sure you didn't fry the impeller since it was probably spinning dry.

06-26-2012, 10:33 AM
Make sure the o-ring is sealed and not crushed. Also make sure your new impeller exactly matches the old one. I just went through this. The "replacement" that was my backup had two notches in the face of the impeller and the old one did not. It would not create the seal needed to pump water and no water was pumping past the impeller. Stumped me for a few mins until we noticed that the impeller was different. I also have a '85 S&S.

east tx skier
06-26-2012, 10:35 AM
Put the intake hose in a bucket. If it doesn't draw water at idle, you put the pump housing in upside down. Always mark pump housing orientation before removing the pump on a PCM engine.

Also, check the sandwiched plate between the two halves of the pump housing. I have been careless once and not gotten the screw holes in the plate lined up with the screw holes on the two halves of the pump housing.

If you determine that you mounted the pump housing upside-down, watch your impeller carefully. If you ran it dry long enough, you may have torched it.

06-26-2012, 05:39 PM
Thanks all....yeah I was thinkning I probably did something backwards. I ran it some most likely shot out the new impeller. I take a look soon as I get back into it.

06-26-2012, 05:41 PM
Here are pix of what it looks like now.



06-26-2012, 08:26 PM

06-27-2012, 09:35 AM
yup mine is backwards. User error- huh TY-

06-27-2012, 11:02 PM
I always remember that it goes in backwards... Then I get it right each year.

The water takes the long way around. If you think about it, it makes sense- the "bump" on the inside of the pump housing collapses the impeller vanes which squeezes the water out. The pump is turning clockwise (when viewed from the front of the engine), so the water enters the vanes, gets carried all of the way around the pump and squeezed out at the top.

I think about this every spring. I made the same mistake as you one year - it got hot fast.