Page last updated July 17, 2008



Common Lower unit diagram

Outboard Water Pump Repair

Just the Impeller or you can replace all gaskets

I initially was doubtful on the lower unit. It was leaking lots of oil and I hoped it was not the lower unit gearcase near prop. After numerous tests utilizing flush device and barrel, I finally concluded that it was the gaskets near the water pump. As you ca see from the pictures below, the pump has a

collection of oil. This is a much easier repair as the lower unit gear case near prop has numerous parts and requires a special fabricated tool to remove, unless you have access to an OEM tool.

Make sure you clean off the area you will working on, have some carburetor cleaner available, gasket remover, shop rags, basic tools as well as some L shaped / elbow wrenches (see below)

Check for waterpump kits or try

Make sure you have ear muffs or barrel to test your results and take your time and inspect all areas of pump housing for sharp protuding areas and file them down. You don't want additional damage resulting. The engine should never be started without water circulating becuase the impeller needs the water to act as a lubricant. If you run for even a few seconds, you risk damaging the rubber impeller.

1. Remove lower unit by removing trim tab, bolt underneath trim, two bolts on each side of lower unit and another bolt underneath wing, right above prop. Total of 5 bolts. If lower unit does not come right off after this and you are sure you have removed all bolts holding lower unit in place, you can try to slowly apply pressure in a sideways manner. If still no luck, try tapping gently with rubber mallet. Downward and side slaps near joints are best. Try to stay away from lower unit gear housing area and thin parts as they could warp and cause sever damage. The Merc 700 was really bad and I banged on it pretty hard and no damage resulted.  
2. Here is the picture of the upper lower unit housing. You can see remnants of oil film
3. Another picture of upper housing for lower unit
4. Remove upper drain plug and flush plug (flush plug will keep impeller housing from coming off)

Flush plug off


Drain oil if you have not already done so. Check for shavings and look for milky appearance when you drain. If you have shavings, you will need to monitor and try to purchase a drain plug that is magnetized so that future shavings are attracted to it.


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