Hope everyone is having a good Fourth of July, took the boat out this morning. Was having problems with the raw water pump (454 mag/bravo). Took it out last week, replaced impeller and oring. Had it on rack with muffs...seemed to be running ok. Put boat in the water, all seemed to be good, plenty of water out exhaust. Took it out for spin, temp started going up had boat towed in- appeared to be no water out of exhaust. I am assuming that the raw water pump impeller went again, I looked at the hoses, no leaks apparent. Maybe just a bad unit. Are these stock plastic ones just junky or something? I will pull it tomorrow and inspect it. How prone are these to failure? What can cause it to fail. I would assume perhaps belt tension or a blockage in the drive. Also I do not have a low water pick up. It is standard. Thanks for any help.

Sometimes when you replace just the impeller and not the the plastic pump housing the impeller will fail in short order, It really depends on the condition of the housing. Just fork up the 80 or 90 dollars for the whole kit (Housing, impeller,wear plate, and seals and bolts) from merc and use soap lube on the impeller and have the vanes positioned properly at assembly time and you will get reliability.

I have the same problem today, the entire housing was replaced before this morning and the impeller went again i really dont know what to look for. Hope someone shines some light on this.
Thanks

make sure you didn't reverse the intake and outlet lines on the back of the pump. on the hose you could have been pumping out what water was left in the block. did it once myself. cost me a pump and a housing, fortunately, not a motor.

Check to make sure the water intake hose at the inner transom assembly is tight. The pump might be sucking air.

did the original impellor come apart? you could have pieces of it blocking the fresh water from getting thru motor.

looked at it again, for awhile when I first reinstalled it, the pump seemed to be working normally. The impeller is intact but seemed like the pump was too hard to turn for the engine. I guess I'll search thru the threads a bit more and hopefully find the answer I am looking for. I think that I will purchase a JAbsco unit and be done with it. A raw water pump is too important a part to screw around with.

Try looking under the fitting on the intermediate housing that the water hose to the pump connects to. The hose from the intermediate housing goes thru a hole in the casting and is held in place by a hollow tapered plastic piece (its the same outside the boat, you have to pull drive away from the intermediate housing to see it). Check that that plastic piece is open (if I remember right the opening is around 1/2 to 5/8 inch). On my boat that plastic piece looked as though it had melted closed (opening was about the size of a pencil), All your water goes thru these. On muffs and low rpm all was ok, When I speeded up, things heated up.

Maybe your problem is basically the same. I would look at both ends of the hose in the intermediate housing for blockage.

If you have external fresh water flush attachments, check to be sure the caps are on tight. If these aren't, they will still work OK with a hose attached. However, in the water, without the forced induction, the loose caps will suck air and the pump will not work.

some of the housings we have been seeing have very sharp casting lines in them...we hand blend the ports to insure longevity and reliability... after the pump sees the original prime, you can have a torn blade and still circulate and or exactly like Steve David stated in the above post.

remember to pre-lube during assembly.