Raw water pump leaking: weep hole drips, impellers and how surveyors write it up

The raw water pump pulls seawater in to cool the engine and the exhaust. When it fails, the engine overheats and the exhaust hose can overheat and burn through. When it leaks, salt water sprays over the front of the engine and corrodes everything below it. Either way, a surveyor wants to see it dry and pushing a good stream out of the exhaust.

How a surveyor checks it

Before starting the engine, look at the pump. Good Old Boat's key sign: most raw water pumps have a small weep hole on the body, and water dripping from it means an internal seal has failed. Look for rust and salt crystals on the pump, the engine bearer and the drip tray below. In the author's case, a slow drip had left rust under the pump.

With the engine running, look over the side at the exhaust. Good Old Boat advises doing it routinely: water should come out with the exhaust in a steady pulse. A weak or intermittent flow means the impeller is worn, the strainer is blocked, or the seacock isn't fully open.

Then the records. An impeller with no record of being changed is due, and a spare should be aboard.

What decides the grade

Flow. No cooling water, or an engine running hot, is an A: the engine shouldn't run until it's fixed. A steady drip from the weep hole is a B, because a leak past the water seal will eventually find the oil seal and the bearings. An impeller with no service record is a C.

What a rebuild involves

Good Old Boat's warning: photograph the pump before taking it off, because it can be refitted upside down and pump the wrong way.

Photos to take

The pump body and weep hole, any rust or salt below, the drip tray, and the exhaust outlet with the engine running. With Axsail, say what you see at the weep hole and the exhaust as you take the photos and they go on the engine finding.

Writing it up

Say whether the weep hole is dry or dripping, the state of the pump body and what's below it, the cooling water flow at the exhaust, the engine temperature on the run, and when the impeller was last changed. With an A, say "do not run the engine".