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Outdrive Water Pump Replacement (Alpha)

Water Pump Replacement Tips

Every Year!

It's a very good idea to replace the water pump in the drive every year, even though the factory recommendations are every two years or 100 hours whichever comes first. When the pump fails, engine damage may occur from overheating. If the engine has already overheated, then you need to check a few things.

The hot exhaust from an overheated engine will actually melt the upper and lower pump housings. It will also ruin the seals in the outdrive!!

All too many times boaters will replace their water pumps after an overheat only to ruin the outdrives from an overheated seal leaking out the drive oil.

If you think the drive might have gotten too hot, have it resealed by an authorized Mercruiser Dealer.

What to Expect

Mechanic's will say: Drive work is difficult and messy. The outdrive is heavy. The best way to replace a pump is to remove the entire drive and have the drive supported upright in a stand. Trying to replace a water pump without the drive supported in a stand sucks. While the drive is apart.... you need to really inspect everything from top to bottom and inside out. Missing one item could lead to drive and/or engine failure. Don't screw up!

Doing It

Place the gear shifter into forward gear. The shifter MUST be in forward to remove the drive! Remove the hydraulic cylinders and the six retaining nuts. Lift the drive by hand a little and let it drop to jar it loose. It may be stuck so use care to get the drive off!

Support the drive by the lower in an upright position in a stand. Remove the drain and vent plugs to let the drive oil drain out.

Now you need to unbolt the upper from the lower. Alpha Ones and Gen 2 drives differ in the fastening hardware. Most important is to note that a bolt is hidden up under the zinc trim tab. You must first remove the zinc trim tab and then the allan head screw from underneath. The Alpha One has two nuts underneath the ventilation plate. The Gen 2 drive is held together with through bolts on the sides.

The two side nuts of the Alpha One are the last to be removed and they will NOT come off all the way until the housings are separated a little.

Sometimes (more than not) the two housings are stuck (corroded) together. If they are stuck, a thin smooth stiff paint scraper works good to get between the housings at the split. Once they start to separate then a thicker screw driver will finish the job.

Lift the upper housing off and out of the way. You may notice a little drive oil leaking around. That's OK. That's the stinky gross gooey smelly drive oil that loves to get in your hair and clothes.

See the pump now? The Alpha One and "R" pumps have a plastic upper housing and the Gen 2 drives have a Stainless housing.

Remove the housing nuts and/or screws and lift the housing off the shaft. Remove the impeller, the key and the wear plate.

The Alpha One and the "R" drives have plastic water pump bases. We strongly recommend that you replace the water pump base! Why not? Your already here so you may as well do it right.

The water pump base has two critical driveshaft seals which go bad so just replace the damm thing.

To remove the plastic water pump base, pry up from both sides with two flat screw drivers and it should pop right up.

Sometimes the bottom round section will stay in the housing. This is screwed up. If you have done it right, you will see NO PLASTIC left in the housing.

Now is a good time to look things over. Look down in the water intake passage and make sure it's clean. Next, flip the upper driveshaft housing upside down and inspect the copper tube and wear it seats. The copper tube seats up in the "water pocket cover" which has 4 bolts. If the water pocket cover looks melted then it should be checked for leaks!

Replacing the water pocket cover sucks BIG TIME because sometimes the bolts snap off in the upper housing. If they snap off.... you will need a new upper housing!!!

It's very important to inspect the driveshaft where the water pump base seals had been riding. If the shaft is worn, grooved or pitted, then it should be replaced to prevent water damage.

Read this carefully!

The Alpha and "R" water pump bases are DIFFERENT! They have different part numbers and will not interchange! They LOOK almost identical but they are not. If you have a pre-load pin at the top of the driveshaft, you have an "R" drive. If you have NO pre-load pin, then you have an Alpha drive. If you have NO pre-load pin and a stainless housing, then you have an Alpha Gen 2.

The Alpha Gen 2 has no water pump base. Only a plastic seal carrier. It's easy to pry out and replace if you feel the need to do so.

Clean the old gaskets from the housings and clean any other crap that might screw this job up. It's very important to make sure all the old gaskets and corrosion bits are removed.

Take a can of Mercruiser Perfect Seal Sealant and coat the housing where the gaskets will seat. Prepare the water pump base for installation by first installing the correct gasket on it making sure the water passage hole lines up correctly and then choose the correct o-ring that fits around the round part in the groove.

Coat the o-ring with Perfect Seal. Take some Mercury Marine Special Lube 101 and fill between the two seals in the pump base. Slide the base down over the driveshaft and firmly snap it down into place.

Now you need to get your act together on how the upper gaskets fit on either side of the wear plate. Take your time and familiarize yourself with how they fit. After you have figured it out, slide the first gasket, the wear plate and the second gasket down.

Now you need to remember to place the water pump impeller key in place! Hold the key in place while you slide the impeller down over it.

Take some Special Lube 101 and grease the inside of the water pump housing cup. As you lower the water pump housing in place, turn the driveshaft clockwise.

Make sure you use the correct washers and mounting nuts. DON'T over tighten the nuts!!!! If you over tighten the nuts you will ruin the water pump.

Install the plastic guide tube making sure the rubber grommet is in there first. Slide the square looking o-ring slinger seal down the driveshaft till it hits the pump housing.

Older driveshafts have a groove at the top for the upper o-ring. Install the o-ring if used.

Grease up all the studs on both drive housing halves. This will make it easier to do next year.


There is a "quad seal" that MUST be installed at the oil passage gallery. If you forget this quad seal, the drive will blow up on its first use. Also... there needs to be a flat washer installed over the small shift shaft. If you forget to put the washer in place, the shift shaft will drop and you will loose shifting at the worst time. Also.... Don't forget to have the zinc bolt in place before mating the housings!


The drive lower and upper shift shafts MUST be in forward position before mating!@! Put the lower in forward gear by turn the shift shaft clockwise and locking the prop shaft in the reverse direction. Once its in forward... don't bump it! If you bump the prop, it will knock it out of forward! Ok... you have the lower in forward... now place the upper shift shaft in forward as well. The upper shift shaft must face fore and aft. That's forward!

Lower the upper housing into place making sure to align the copper tube into the plastic guide tube.

Did you knock the thing out of forward? Check it! Turn the u-joints so the splines line up and the upper will fall into place. You must FIRST separate the housings just enough to get the side nuts on! After both side nuts are installed, then instal the front nut, the two underneath, the allen under the zinc and snug them all up. It's a good idea to check your shifting before going any further. In forward.... the brass shift rod will face fore and aft.

Now.... get a pressure testing pump and pressure test the drive to 15 PSI. If you don't pressure test the drive then don't cry when oil leaks out. You really really need to pressure test the drive. Trust me on this.

Fill the drive with Mercruiser Drive oil from the bottom until it overflows out of the upper side vent plug hole.

Make sure the drain plugs have perfect gaskets and are snugged up tight.

Place the new drive gasket and all the new mounting o-rings in place. Check to see that the shifter is in forward and that the drive is also in forward and install the drive.

Test run on a garden hose with a good flushett before launching.

It's a good idea to recheck the drive oil after the first use!