Here’s how I do the Optimax 2.5L water pump. Recommended service interval is annually or every 100hrs whichever comes first, if you fish/boat in dirty or debris laden water, you may need to service more often. I highly recommend a genuine Mercury service manual, if you don’t have one, support those who help us and order one from European Marine.
For water pump service I leave engine in neutral be sure you do not rotate engine or driveshaft during removal you will see why shortly.
Remove the lower unit, there are 5 nuts, 3 of which are visible from the top, one at nose and one each side
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and two below on the aft end of lower unit.
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There are also 2 bolts, one that attaches the round anode plate, pop plastic cover off to access, and another under the plate (pic was blurry so will add later). You will have to depress the black plastic ring on the Legris fitting to remove the pitot tube.
With the lower unit supported so you can work freely, the very first thing I do is clean the driveshaft just above the housing with lacquer thinner, acetone, Brakleen or other suitable solvent. Once the solvent dries take a Sharpie and make a mark directly in line with the front stud and/or onto pump housing.
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Now remove the 3 nuts, one screw, and lift housing off impeller. Slide the old impeller off, save the key (or use the new one if you bought a complete kit), then remove the plate and both gaskets.
housingoff.jpg
Next step is to remove the pump base under which you’ll find the 3rd gasket, it takes some wiggling but isn’t difficult to remove. There’s a ledge at the rear of the pump base I use a right angle pick tool to lift same time I work the front with a flat blade screwdriver.
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Clean and inspect the pump base, plate, and pump liner. If the plate
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and insert
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are not scored, they are fine to reuse (those pictured are on their 3rd season). Don't be concerned about marks at center where the impeller contacts plate and insert.
Replace the o-ring and lubricate lightly before reinstalling pump base.
o-ring.jpg
Install the new bottom gasket followed by the base. Just as with removal, it takes a little effort, a ½” wooden dowel or hardwood block with a clean square edge can be used to lightly tap base down as the new o-ring will be tight.
baseinstalled.jpg
Once the base is fully seated, assemble the top side, gasket, plate, gasket. Next, I liberally lube the pump insert with liquid dishwashing soap. Dawn is often mentioned but in reality, any viscous liquid dishwashing soap will work and I have used others with equal success. Slide the impeller onto the driveshaft, hold the key in place, align the slot, and slide impeller down until it seats against the plate. Next slide the housing down the driveshaft until it just contacts the impeller and while placing pressure on top of the pump housing rotate the driveshaft in a clockwise direction, it should seat within a turn or two. Align your index mark, if you have not rotated engine, the lower unit will slide in effortlessly.
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Install cover nuts (torque to 48.6in lb) and the screw (torque to 35in lb).
Rotate driveshaft clockwise so the index mark lines up with the front stud and you’ll be assured the driveshaft and crank splines will be perfectly lined up when you stab the lower unit. Before reinstalling, clean any old grease from the drive and shift shaft splines, re-apply a light coating on both making certain to wipe any excess off the top of both and don't forget to run a bead of high temp silicone on the divider behind the pump base, very important!!
I install the water tube in the engine first, makes it easier for me to line up with the pump than at bottom of powerhead. Ensure shift rod lines up with shift shaft as you raise lower unit (don’t forget to insert water pressure line in the Legris fitting). Lift lower unit as far as possible then run top 3 nuts down to hold lower while you finish. I’ll pull lower most of the way up, alternately snugging the first 3 nuts, thread on the 2 nuts at rear, and then tighten all. Install the bolt under the anode plate then torque all fasteners (a 16mm torque adapter is required for the two nuts on either side of the lower) as follows – all nuts 50ft lb, bolt under anode plate, 27.5ft lb, and anode plate retaining bolt – 25ft lb. Snap plastic cover on after torquing anode retaining bolt and you're done.
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Originally Posted by ridgerunner4545
