How to Fix a Sterndrive or Outboard Motor Water Pump
YOUR OUTBOARD'S OR STERN-DRIVE'S water pump could quit right in the middle of the season, when service technicians are swamped, causing you to miss weeks of boating. But you can fix it yourself in an hour or two with the right tools.
1. Remove the bolts that fasten the lower unit to the midsection. Disconnect shift linkage. Slide the housings apart. If they won't pull apart, look for any bolts you may have missed.
When trying to separate housings that have corroded together, never use force. Just get a bigger hammer--in this case, an oxyacetylene torch (a common propane torch doesn't put out enough heat). Warm the parting line, then let it cool for an hour. Heat it again and let it cool. This expansion and contraction breaks the corrosion, allowing removal. If you must hammer the cases apart, use a rawhide mallet, not a ball peen hammer (which can crack the cases). If you can't split the cases, take them to a dealership.
2. Once the cases separate, look for bronze locating pins. Some motors have them; others don't. Save the gasket if there is one--it prevents corrosion from gluing the case together.
3. Remove the four or five bolts that secure the water pump housing to its base. Lift off the housing, the impeller and the thin, stainless steel base plate. You will likely find a bad impeller-one with stiff or missing blades. Examine the base plate and the interior of the housing. Look for scoring caused by sand sucked into the system. Replace all the components now: It's cheaper than redoing the job later.
4. Some drive shafts have an O-ring on the end that slides up into the engine. Shine a flashlight inside the motor, making sure the old one isn't lodged inside the crankshaft's internal spines.
5. Grease the drive shaft splines. Carefully align the water pump tubes and slide together. Reattach the shift linkage, and coat the threads of the bolts with anti-seize compound to make subsequent disassemblies easier. Do not overtighten the bolts or you risk stripping the threads.
6. Check the gear case oil, looking for any sign of water intrusion. If the seals are bad, now is the time to replace them.