40 Mercury Burning up Impellers

Hi Needs some Help, Just bought a 40 hp Merc and 13 ft Whaler. Motor did not run, My Mechanic put in fresh gas ran good did not pump water.Removed lower until and installed new water pump kit. Started motor pumped water just fine. I started motor the next day no water.Mechanic then dropped lower unit impeller was destroyed. Then removed thermostat ran without it installed ANOTHER new impeller. Before this ran compressed air through motor let some vinegar sit in block for a few hours. Put all back together AGAIN Started motor ran real good pumped water great. Mechanic left and I put a barrel under motor started up and did not pump water again it did exactly the same thing again. pumping on the first start then no more water. I assume when the lower unit is dropped I will have a destroyed impeller?? Can anyone help me I do not want to put anymore money in this. I have not called my mechanic yet. I was hoping to get some feed back her Thank you for any assistance you can provide.

Re: 40 Mercury Burning up Impellers

Hummm, Have you inspected the impeller housing for any damage or deformaties? Is it possible that you may been using the wrong parts? could something be clogging it up so water is not getting to the impeller? Its really weird that one run would shread up an impeller. when i installed mine i had to slowly turn the shaft in the same direction the engine would turn it
(i dont remember what direction that is) making sure each leg of the impeller was curving the correct way. For example if the shaft turns clockwise each leg of the impeller would curve to the left. I also used a small amount of quicksilver multi-purpose lube in the housing and the surfaces of the impeller when installing it. Finally, not saying you did this. just some FYI you should never run the motor without the ears and running water.

Re: 40 Mercury Burning up Impellers

Thanks for the response. Mechanic used a new kit when he installed the new impeller the first time. I believe this comes with a new housing.One thing I forgot to mention this is a salt water motor. I blew compressed air myself from the thermostat and it did blow out through the hole at the bottom of the block down in the cowling.Its so strange if its blocked up somewhere why does it pump on the first start?2nd impeller change he did not change the housing because it looked good.

Re: 40 Mercury Burning up Impellers

Any small deformity in the housing or on the wear plate will munch an impellor. It does'nt matter which way you turn it putting it in as it will correct itself when the motor turns it. Did you blow air out through the water pick-up tube? if there's any trash in there it can get sucked into the housing and cause damage also.

Re: 40 Mercury Burning up Impellers

Yes He blew air from the bottom tube up sounded clear.Why would it Pump Great on the first start up? Then nothing Thanks again for any help.

Re: 40 Mercury Burning up Impellers

It pumped on start-up because the impellor was still in one piece. There is something in there that is not right if its eating them. Look for a burr, grooves the wear plate installed incorrectly, ect.

Re: 40 Mercury Burning up Impellers

Another option is you don't have enough water in the "tank" to cover the water pump inlets, or there's a suction fault in the water pump that breaks the prime. (base gasket for instance)

If you've lunced 2 impellers in the same housing, likely the housing and baseplate are bad.

If you're in the habit of "popping it off" dry to see if it'll start, that alone will usually immediately lunch the water pump.

hope it helps
John

Re: 40 Mercury Burning up Impellers

Guys Thanks for responding, But if a complete new pump kit was installed doesn't that have a new housing and base plate. Or the new baseplate is defective?I read something about a nylon bushing? under the power head that can melt? and cause a restriction? any thought on that theory but If I understand correctly it sounds like the pump is falling apart from something within the housing? Or is it more likely to get destroyed from back pressure from a restriction under the powerhead or passage forcing pressure on the impeller? Thanks again

Re: 40 Mercury Burning up Impellers

More Info I took off the screen on the bottom of the lower unit where you attach your muffs. Two chunks of what looked like a cast metal inside does anyone know what is this is? where did it come from? thanks again

Re: 40 Mercury Burning up Impellers

May have been parts from the old impellor or housing. You may have found all or part of your culprit. At least its a good clue.

Re: 40 Mercury Burning up Impellers

Found what I think is the issue. Pieces of cast metal that were in the suction area on the bottom of the lower unit broke off from the lower unit next the the water pump housing. I guess it was sucking air. All the more reasons for flushing with fresh water.Thanks to everyone for your assistance. This site was a huge help to me.