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cmattj wrote: Wed Aug 16, 2017 1:37 pm Merc 496 fresh water pumps with wear can leave a edge on the face plate that when a new impeller get installed the fear is it cavates or is ineffective at higher speeds with all the groves on the pump side out.

Its common with most cast pumps that have had an impeller fail or just wear on the end plate. Most shops recomment replace the complete unit and with your closed cooling system that is $$ as the 496 merc closed cooling have air dump winterizing pop off lines and sensors and are more complex.

My fix is I have that top wear plate machined down (yes it gets thinner) but its ok as it still bolts down and seals. cost $30.00 bucks. and all the stock merc impeller kit work fine.

If the inside housing gets worn wich is less common then you throw it away. Ive never like those kits that come with shims and reduced impellers as I would just go after market at that point..

Stll an easy fix.. dont throw it away untill you inspect it. Boatmasters here in livermore, ca has them on the shelf ready to exchange.

cmattj wrote: Wed Aug 16, 2017 2:42 pm I do miss water pressure gauges.. I could see at idle 1 to 3 psi and at 3200 rpm it was 20lbs when fresh.

The kits would use a shim insert the housing and add a spacer to the back plate to hide groves in both ends where the impeller contacted..

I used one on my 22 classic but only ran it a few hours before I sold her so not sure how it lasted.

Keep in mind if the main body ( pulley side )has no wear I suggest you machine the backing plate so you can use the oem merc impeller kit .

Have you found anyone to come by and scann?
Then can do it key on not running for codes and some system read water pressure if you can have some one go out with you.

cmattj wrote: Wed Aug 16, 2017 3:37 pm Donzi 22 1987. 502 mag..Xr..Restored her and had it for many years.. Loved it (Sorry for the Donzi pics.. couldnt help it)
You tell my favorite color is red.. My 282 is my 5th red boat. Wife thinks I need to expand my thinking..(maybe burgundy?)

Im glad you found someone to Scan it.. There is a ton of seasons left and i know little bugs like this can be discouraging but they will be forgotten soon!!

cmattj wrote: Wed Aug 16, 2017 3:59 pm You got it!! swim platform... whats that??. Strap eye hook and a out drive was all as you know.. very nice pal. Love the lines in white!

AsLan7 wrote: Wed Aug 16, 2017 1:52 pm

cmattj wrote: Wed Aug 16, 2017 1:37 pm Merc 496 fresh water pumps with wear can leave a edge on the face plate that when a new impeller get installed the fear is it cavates or is ineffective at higher speeds with all the groves on the pump side out.

Its common with most cast pumps that have had an impeller fail or just wear on the end plate. Most shops recomment replace the complete unit and with your closed cooling system that is $$ as the 496 merc closed cooling have air dump winterizing pop off lines and sensors and are more complex.

My fix is I have that top wear plate machined down (yes it gets thinner) but its ok as it still bolts down and seals. cost $30.00 bucks. and all the stock merc impeller kit work fine.

If the inside housing gets worn wich is less common then you throw it away. Ive never like those kits that come with shims and reduced impellers as I would just go after market at that point..

Stll an easy fix.. dont throw it away untill you inspect it. Boatmasters here in livermore, ca has them on the shelf ready to exchange.

Great info Matt! Thank you.

When you say "you do not like the kits/reduced impellers/shims, etc"....this is not the same as the entire housing that is sold on the performance link above, correct? What are your thoughts on those "improved" sea pump housings?

I'm just curious if my possible lack of water pressure (which I believe to be the case) on plane is causing the alarm to sound because the new impeller and new tube thru the gimbal which carries the water cannot keep up while on plane due to housing wear. Hoping the marine tech can confirm this issue.