Yanmar Impeller Change Frequency Question

[Wotname]

Many have mentioned "the Yanmar raw water pump"; this is reminder that Yanmar doesn't manufacture any raw water pumps. They use other manufacturers pumps and which pump is used on what engine is dependant on the country of sale and the engine model.

In some cases, it can depend on the year of sale even within a single engine group. For instance, in Australia, a 2GM20 can have different raw water pumps depending on the year it was sold.

Yanmar dealers do get it wrong (even Yanmar distributors). I purchased my current 2GM20 new complete with a "spares" pack and the impeller they supplied as a spare was the wrong size. Initially I thought they simply picked the wrong part number but no, the part number supplied was for a 2GM20, just a different serial number range.

The lesson is, if you gat a spare impeller or even a spare pump, check that it fits before leaving the dock.

[Copacabana]

Originally Posted by Kenomac

Do you carry a spare engine water pump onboard? I was considering the purchase of a spare at $400. My engine has 1900 hours.

Kenomac, if it's within the budget, it's a great spare to carry if you are away from chandleries/mechanics on your cruise. The rebuild kit is great to carry, but it takes some time to rebuild the pump. If you need the engine right away (to leave an anchorage before weather for example), then a spare pump is the best. I believe raw water pumps don't often fail catastrophically, but rather develop a slow leak that then ruins the bearings (and often sprays water around inside the engine compartment!). I'm going to buy a spare on my next trip abroad for the spare kit. It's easy to swap out if something goes wrong with the old one.

My previous boat gave me so many heartaches with the raw water pump (I tried to do it "on the cheap" and rebuilt it about every 3 months. In the end I gave up and bought a new one. The wear on the shaft and scoring on the inside was the problem I think.

+1 on the Speedseal Life! It pays for itself in saved impellers!

[OceansFive]

Here's a drawing from my book Marine Diesel Basics 1 showing what to look for when inspecting a rubber/nitrile impeller.

The impeller does not need to be changed on a time schedule (unlike coolant/antifreeze for example? but best practice is certainly to 1) inspect the vanes carefully once a year and 2) remove the impeller during any prolonged lay-up (winterizing).

Even if there is still plenty of raw water coming from the engine exhaust, a torn, cracked or pitted impeller is likely to fail sooner rather than later and should be replaced.

The vanes that stay compress inside a raw water pump over winter or during any lay-up will get a permanent bend (a "set") and will not seal properly when the pump is used again, leading to reduced water flow through the engine's heat exchanger.

More drawings in my profile here.