Spring Refit - Replace engine impellers!

[chrismunson]

It looks like an early spring here in Virginia. While you are preparing your boat, do not forget to change the water pump(s) impeller. They last one year, and over the winter they dry out, become stiff, and can disintegrate and block your cooling system. Do not even test-run your engine, change the impeller first.

[Sula]

Impellers can often (but not always!) last much longer than one year in my experience, and as reported by friends and by others on sailing forums. By all means replace annually if you are so inclined.

I used to replace them annually 'just to be on the safe side', but after accumulating a large collection of only very slightly worn used 'spares', being on a increasingly tight budget, and knowing of others that had satisfactorily habitually used theirs for numerous years (10 + years, one person told me), I'm now using mine for longer.

Certainly impellers should be carefully inspected annually - look for cracks in the blades, especially at their roots; for wear and damage on the tips of the blades or side faces of the impeller; and check the rubber moulding is firmly attached to the central metal 'hub'. Ideally, remove the impeller from the pump when the engine is laid up, so it doesn't take up too much of a permanent set bend to the blades. When installing an impeller lubricate it with water or the special grease now often supplied with the impeller (it doesn't matter which way the blades are facing when you put the impeller in, they'll flip over if they're the wrong way round).

Impellers will tend to wear faster in silty water than clear, if the water supply has become restricted (e.g. inlet clogged) or impeller has been run dry (e.g. forgetting to open inlet seacock), or not lubricated (whether by water or suitable grease) when installed or after engine has not run for a long time. Excessive heat, or freezing can damage them. Of course engine running time will be a factor.

Occasionally an impeller may fail early due to poor manufacture (which is a particularly important reason to inspect them periodically), but generally, in my view, they are pretty robust.

Chris is right, if they do fail they can block (usually only partially) the cooling system. I've never had the problem, but hear that the broken off bits will usually be found in the heat-exchanger if you have indirect cooling. Much less likely to be a problem (or ever be found!) if you have direct cooling.