Outboard Water Pump Servicing, Brand by Brand

Every outboard on the market, from a 4hp kicker to a 300hp V8, cools itself by sucking seawater up through the leg with a rubber impeller. Every one of them will eventually kill that impeller. And on an outboard the warning you get is unusually clear — the tell-tale stream stops.

How often does an outboard water pump need servicing?

The common workshop answer is annually, or at every scheduled service, whichever comes first — and your owner's manual sets the actual interval for your motor, which is the one to follow. Some manufacturers specify a fixed hour figure, some a period in years, and most tighten it up for engines used in salt water.

What is universal is that the impeller ages sitting still. The vanes rest bent inside the pump housing, and rubber left bent takes a set. A boat that sat all winter can have a worse water pump than one that worked all season, which is why "it has hardly done any hours" is not the reassurance owners think it is.

The signs, in order of how worried to be

• A weaker tell-tale than you are used to. Learn what yours looks like when healthy; the change is what matters, not the absolute size of the stream.
• A hotter-than-normal powerhead, or the overheat alarm sounding at higher revs but not at idle.
• Intermittent tell-tale that comes and goes as you change revs.
• No tell-tale at all — shut down immediately. Running an outboard without cooling water damages it in minutes, not hours.

One caution: a blocked tell-tale tube is a common and harmless cause of a missing stream, and people have pulled apart perfectly good water pumps because of it. But you find that out with the engine off, not by carrying on and hoping.

Why the whole kit, not just the rubber

A water pump kit contains the impeller plus the wear plate, the housing or liner, gaskets and seals, and the small key that drives the impeller. It is tempting to fit the impeller alone and save a little. It is also how people end up doing the job twice, because a new impeller running against a scored, grooved wear plate cannot seal properly and wears out early. The labour is in dropping the gearbox; the parts are the cheap part.

The other rule, familiar to anyone who has read our guide on when to replace an impeller, applies just as much here: if the old impeller is missing vanes, find them. Fragments travel up into the powerhead cooling passages and the thermostat, and an engine that overheats again with a brand new pump usually has the last one's remains stuck somewhere upstream.

Brand by brand

The principle is identical across every make; what differs is the kit and how much has to come apart to reach it.

Mercury and Mariner water pump kits, along with oils and service parts, sit in the Quicksilver range — Quicksilver being Mercury's own parts brand, so these are the factory items.

Yamaha parts, including pump components for the four-stroke and the older two-stroke ranges, are in the Yamaha marine parts range. Yamaha owners should note that on many models the water pump sits under the upper casing, so the job includes dropping the lower unit and handling the shift linkage carefully on reassembly.

Evinrude and Johnson pump parts are in the Evinrude and Johnson BRP range. With BRP having wound up outboard production, keeping these engines cooled properly matters more than it used to — parts are still available but worth planning ahead for rather than sourcing in a panic.

Suzuki owners are covered by the Suzuki marine parts range, and we stock Honda outboard parts as well. For older, orphaned and less common motors it is worth asking — aftermarket impeller kits cover a lot of engines whose manufacturers no longer support them.

What running it dry actually costs

It is worth being blunt about the consequences, because outboards are less forgiving here than inboards. With no cooling water the powerhead temperature climbs fast. Pistons expand against cylinder walls and pick up, and on a two-stroke the exhaust-side piston is usually first to go. Even a short overheat can glaze bores, cook the thermostat and harden every seal in the cooling circuit. That is the difference between a modest pump kit and a rebuild, and it is decided in the couple of minutes between the tell-tale stopping and the engine being shut down.

The habit worth building is simply this: look at the tell-tale every time you start, before you leave the ramp. It costs nothing and it catches the failure while the boat is still tied up.

Salt water asks a bit more

Flushing after every trip in salt water is the cheapest maintenance there is. Salt crystallises inside the cooling passages as the engine dries, and those deposits gradually restrict the same narrow galleries the impeller is pushing water through — so a motor that is never flushed ends up with a cooling system working against itself even with a healthy pump. Run fresh water through the flush fitting or muffs until the engine is cool and the water runs clean.

The same applies to the thermostat, which is often overlooked. A thermostat stuck partly closed produces exactly the symptoms of a tired impeller, and it is a fraction of the cost to replace while the engine is already being serviced.

Getting it done

A water pump on a small outboard is a reasonable home job with a manual and some patience. On larger motors it gets less forgiving: the shift linkage has to go back correctly, the driveshaft splines want the right grease, and the impeller must be fed into the housing turning the correct way or you will shear vanes on the first start.

We do water pumps across all the common makes as part of outboard servicing and repairs at the Kadina workshop. If you can tell us the make, model and year off the engine's plate, ring 0412 532 984 and we will get the right kit for your motor rather than the one that nearly fits.