Seawater pump impeller replacement

Most boaters seem to fall into two categories: those who practice preventive maintenance and those who practice breakdown maintenance. Proceeding directly to the point, those in the first category unfailingly renew their engine raw water pump impeller every two years and consequently never get to see what a failed impeller looks like. I was a faithful member of the first category until we launched Cormorant, our Corbin 39 cutter, last spring and the engine refused to pump cooling water when first started. Replacing the impeller was high on my list of commissioning chores, but I thought that I could at least wait until Cormorant was snugly tied in her marina berth.

High drama was avoided as I had a spare impeller aboard and a Jabsco Model 50070-0200 impeller puller in my tool box. First, I closed the seawater valve to the engine. After gaining access to the water pump, the rear cover was quickly removed and the impeller puller adjusted to fit into the cavity of the pump. Then the two fingers that grip the impeller were adjusted tightly and the drawing screw was taken up to pull out the failed impeller. The whole process took less than 30 minutes and no knuckles were de-barked. Compare this painless task with the typical use of two screwdrivers and many non-printable adjectives, and the price of the impeller puller is then insignificant.

Once you have removed the old impeller, inspect it for missing vanes. They will be found somewhere in the cooling system, probably at the inlet to the heat exchanger. Track them down now as they will cause mischief when you can least afford an overheated engine.

Try this tip when installing a new impeller: determine the direction of rotation of the impeller by bumping the starter or pulling the engine over by hand (or by having a look in the engine manual). Tighten a hose clamp over the new impeller — make sure the vanes are all in the trailing position rather than otherwise. Lubricate the impeller and pump cavity with glycerin — do not use petroleum-based lubricants unless the impeller manufacturer states that these are acceptable. If no glycerin is available, try using a bit of personal lubricant such as KY (this stuff works wonders on installing hoses.)

Inspect the cover plate for corrosion and wear. Most covers can be simply reversed if the impeller has worn a depression on one side. This will buy you plenty of time to order a replacement cover plate. Replace any O-rings or gaskets. Clean the bolt threads and lubricate them with an anti-seize compound before reinstalling them. Using a black felt tip marker, draw an arrow on the impeller cover plate indicating the direction of rotation for next time!

Remember to open the seawater valve to the engine, and after the engine is started, check to make sure that water is coming out with the exhaust gases. Also check the pump to make sure that it is not leaking. Finally, write up your action in your maintenance log and order a new impeller and gasket or O-ring.

There are three sizes of Jabsco impeller pullers. Make sure that you get the right size for your engine. The model numbers are 50070 — 0040 for impellers up to 2.5 inches in diameter, — 0200 for impellers from 2.5 to 4.5 inches, and — 0080 for impellers up to 2.25 inches. The prices range from $45 up. New impellers are specific to your engine and are in the neighborhood of $40. Using the impeller puller, the replacement can be done in less than a half hour, assuming that you have at least average mechanical skills.

Harry Hungate and Jane Lothrop live aboard their Corbin 39 cutter
Cormorant, and are cruising in the Mediterranean in 2011.

More articles by Harry Hungate:
Upgrading Yanmar oil pressure gauge and sender

Diesel fuel lift pump rebuild

Cool your alternator

Shore power plugs outside North America

Voyaging communications report: Cormorant

By Ocean Navigator