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EATING IMPELLERS

dara64

New member
"I have 1982 sterndrive merc 4

"I have 1982 sterndrive merc 470 , This is the second impeller in a month and the boat was only run once for a test run. It has been running hot,changed cam seals, checking everything out, and the new impeller was thrashed again.It just seems like the last impeller was sooooo tight in the pump housing but it was the correct part.any ideas?"
 
"Check the Impeller housing. I

"Check the Impeller housing. Its always a good idea to replace the complete water pump- Upper Housing and Base, when replacing the impeller."
 
Have the 2 impellers been in o

Have the 2 impellers been in one piece? May be a chunk lodged in the water path. Heat exchanger clean? What temp. is the engine running? What is the condition of the antifreeze?
 
"Yes housing was replaced both

"Yes housing was replaced both times.
Raw water impeller.
Exchanger clean ,anti freeze new,getting to 190 very fast, one impeller in pieces the other the fins all broke in the same spot but didnt come apart"
 
You need to find the chunk tha

You need to find the chunk that is stuck. It may be in the brass water tube or the water pocket. It could be between the exchanger and the impeller. Drop the lower unit and backflush from the exchanger. Test the thermostat for proper operation.
 
"yeah did all that, when you p

"yeah did all that, when you put the new impeller in should it be really tight in the housing. I hate to take the cover off the water pocket for fear of the easy snap off bolts."
 
"The impeller should be very t

"The impeller should be very tight fitting, to the point where it is difficult to install. You should use a little lubricant on the ends of the impeller so it can spin until the vacuum pulls raw water into the pump.

If your impeller is tearing up, the usual cause is that there is no water getting to the the pump.

First, make sure the intake valve by the through fitting is fully open.

Second, take the intake hose off the input to the water pump. If there is no blockage, the raw water should start free flowing in force out of the hose end and into the bilge.

Those are the first two things I would check."
 
"Ok will do thanks [img][/img]

"Ok will do thanks
"
 
Does it run at 'normal tem

Does it run at 'normal temp' on the hose & muffs and only 'eats' the impeller after pushing the boat thru the water?
 
"No this last one it started t

"No this last one it started to heat up on the muffs. I am wondering if I didnt get enough pressure from the muffs and it burned up.I think I need the rectangular ones,my round ones dont fit over the holes well at all.It is an older drive a pre-alpha."
 
"I asked as I had an old 165 t

"I asked as I had an old 165 that would overheat before it would get out of the channel from the ramp. It would 'eat the impeller'. back on the trailer and to the shop. no obstruction, new impeller. Ran on the muff & hose for an hour. Once off the trailer, overheat.......

Turned out to be an inlet manifold leak causing it to run lean. Don't know why it destroyed the impeller but it was consistent. New gasket and it never did it again."
 
"Hmmm well we did have the man

"Hmmm well we did have the manifold off recently, so since Im checking everything else I may check into that to.
thanks !"
 
WE found it due to the very sl

WE found it due to the very slight whistle it was making around 1000 rpm. I moved my hand (onto the manifold) and it stopped. Carb cleaner confirmed it as a leak....one of the more bizzarre issues I've seen.
 
"The merc master mechanic spec

"The merc master mechanic speculated that the lean condition was impeeding the water flow and inducing cavitation at the impeller. Being as water is 'uncompressible' I don't understand it either....I figured after he 'bought' two water pump kits, he'd have no reason to offer up his best guess."
 
"important not to overtighten

"important not to overtighten the housing bolts. use a torque wrench. manual should give torque value, my IL6 calls for 70 in lbs, that's 7 lb pull on a 10" wrench."
 
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