June 10, 2019

Impellers An older worn-out impeller. Note that the vanes are bent - a new impeller will have straight vanes that need to be bent in place to fit.

If you’ve spent any time in a boat yard during spring commissioning season, you won’t find it out of place to hear the roar of the engine, a cloud of blue smoke erupt, and a mechanic craning over the stern to look at the exhaust. What they’re looking for are signs of water exiting with the exhaust: Water exiting means that water is being sucked up and pushed through the engine appropriately – this is the only visual clue that the raw water cooling system is working appropriately.

This is true for inboards, outboards and stern-drives, whether power or sail.

The marine engine’s cooling system is pretty basic. Water is sucked up from the water surrounding the boat, is run through the engine, and out through the exhaust system along with exhaust gases. There aren’t too many complicated parts to the system, and one of the seasonal maintenance tasks that is necessary is to check the impeller: A small rubber device (similar to a paddle-wheel) that is spun by the engine, sucking water up, into and through the engine.

The impeller is pressed tightly into the housing of a water pump, and over time it loses its fit, and the rubber vanes can crack or degrade. Additionally, any overheating of the water pump will cause the impeller to break up into small bits. The impeller is the only device to provides the suction and pressure to move the water necessary for engine cooling – and without it working correctly, the engine will overheat.

Depending on the type of engine, the impeller could be located in a few different places:

Impellers The triangular shaped plate covers the impeller on this engine-mounted water pump on a Yanmar diesel

Impellers
Inboards – as found on most sailboats, and on powerboats with a prop and shaft set-up. To find the water pump, trace the hose that runs from the seacock (where water enters the boat), to the first place that it clamps onto the engine: This will be the water pump. Behind the flat plate on the face of the water pump will be the impeller

The lower unit of an outboard engine. The water pump is mounted at the top of the lower unit, at the base of the shaft.

Outboards – Outboards draw cooling water through a vent at the bottom of the drive leg. Half-way up the leg of the outboard, there are a number of bolts that connect the lower unit to the upper. The water pump is found inside the leg, between these two halves. To get to it, the bolts securing the lower unit need to be removed (the owners manual should be consulted), the lower unit taken off, and the plastic casing of the water pump unbolted. The impeller is found beneath the casing.

Sterndrives: Stern drives function similar to an outboard drive leg: Water is sucked up through the vents near the propeller, and forced through a water hose into the engine. Each major stern-drive manufacturer uses a different way to mount their water pumps

OMC: The water pump is behind a casing at the top of the stern-drive. Three bolts hold the casing in place. Once removed, the water pump is accessible. A few bolts later, the impeller can be accessed and changed.

Volvo: These stern drive units have vents similar to outboards and OMC drives, but the water pump is mounted to the front of the engine. To locate it, follow the hoses that run from the stern drive, along the underside of the engine. The water pump can be taken off the engine by removing a few bolts. The back of the pump can then be taken off, to access the impeller

Mercury/Mercruiser

Alpha: Alpha drives have a set-up similar to most outboards: The lower unit of the drive needs to be removed to access the water pump

Bravo: Bravo drives are similar to Volvo drives, with an engine mounted water pump.

ImpellersA handy tool to remove an impeller. The forks pull on the back of the impeller as the screw is turned (pressing on the water pump shaft), forcing the impeller out.


When removing an impeller, space is sometimes limited. There are a number of handy tools that can be used to extract a stuck impeller (in a pinch, a pair of screwdrivers tend to work well). If the impeller has cracked, or has pieces missing, try your best to find any missing pieces. If they aren’t visible, they may have made their way into the engine – so take care to flush the engine through to ensure that rubber bits aren’t blocking any cooling passages!

When installing the new impeller, there are a few things to watch for:

1) Take note of which direction the impeller blades were bent on the original impeller. Try to mount the new impeller with vanes bent in the same direction

2) Most impellers that are mounted to a shaft are held in place by a small metal key. Make sure the key is replaced in the same orientation that it was removed.

3) Lithium Grease is your friend – it will help you to slide the impeller in place, and will help it to turn freely once installed.

Most service shops with a parts department will have ready access to impellers of all shapes and sizes. If in doubt, the engine’s model and/or serial number can be used to easily look it up.

Understanding how your engine’s cooling system works can allow you to catch and prevent costly damage in the event of a problem – and the ability to check and change an impeller on your own can allow you to maximize your time on the water this boating season.

Andrew McDonaldAndrew McDonald is the owner of Lakeside Marine Services – a boat repair/maintenance firm based in Toronto. Andrew has worked in the marine industry for 12 years and is a graduate of the Georgian College ‘Mechanical Techniques - Marine Engine Mechanic’ program.

Questions or comments for Andrew? Email him directly via: This email address is being protected from spambots. You need JavaScript enabled to view it.

Related Articles
Maintenance
  • 08 January 2020
  • By Ethan

Ask Andrew – Shrink wrap

In Nov 2019, I was fortunate enough to attend the Boating Ontario conference in Niagara Falls ON. This conference is geared to members and suppliers of the marine industry particularly marina...

Lifestyle

  • Prev
With old boats every repair seems to uncover something else needing attention.  Removing the ...
We admit it, this Photo of the Week shot was just too cute to resist even though it was blatant ...
Reader Lorraine Gentleman took some liberty with our request for Photo of the Week shots from the ...
This afternoon portrait of her son enjoying a snooze in a pretty unlikely spot comes to us from ...
I've been cleaning dresser drawers for space and came across this 1979 LYRA t-shirt. This was my ...
Our Photo of the Week comes from one of our CY team members who writes “This is my son and his best ...
This boat carries the distinction as the last boat to leave the C&C Custom shop in Oakville ...
We crossed Lake Ontario from Oswego with a minimum of fuss and did a little happy dance when we ...
Our Photo of the Week comes from Mark and Lisa Harris who winter in Vancouver, Washington and spend ...
I am new to boating. Bought a 2019 Ranger Tug in April followed by taking a short boating course ...

Boat Reviews

  • Prev
With a philosophy of quality and 'doing things right Ranger Tugs launches the all new R-25 at the ...
The new Beneteau Swift Trawler 41 renews the spirit of the practical seaworthy cruiser. The ...
The Canadian Yachting test crew last week had the opportunity to run the Bavaria S36 HT at St ...
ILCA is seeking new builders to complement its existing network of manufacturers, the International ...
Nelson Gilbert (1854-1921) began building canoes in Brockville in the 1890s, a time when the sport ...
I have heard a lot of talk lately about trends in yacht clubs where senior membership is getting ...
To get you in the mood for cruising the Boat Show then launching in spring, here’s a boat that ...
Quite simply, the styles of boats have changed. Where in past years a buyer might have been looking ...
At the boat shows, the Ranger Tugs’ classic tugboat lines always grab the crowds, with the wives ...
Sometimes a great idea requires an encore, and French yacht builder Jeanneau got that with the ...

Pursuit DC 235A Great Boat for Canada and Mom Approved Too!

By Jill Snider and Andy Adams

Coming from two different directions, Jill Snider and I met up at Crates Lake Country Boats in Orillia, Ontario to run and review a new Pursuit DC 235, a deep vee dual console boat that is an offshore inspired bow rider with strong fishing overtones and a wide range of family features.

It’s what I would call a handsome, classically styled boat that I suspect will still look fresh many years into the future. Jill had a different take on it.

 

Read more about the Pursuit DC 235.....................

Destinations

  • Prev
Boom & Batten Restaurant is suspended over the water adjacent to the Songhees Walkway and ...
Provincial Boat Havens are those special places to drop anchor in British Columbia’s West Coast and ...
NW Explorations, a Bellingham, Washington-based yacht charter, brokerage, and marine services ...
If you haven’t cruised the Rideau Canal before, you have missed a special treat and even if you ...
At the 2019 Vancouver International Boat Show I had the pleasure of meeting up with Allyson and ...
Following the harsh impact of Hurricanes Irma and Maria, The British Virgin Islands is making an ...
For the adventurous boater Bunsby Marine Provincial Park is a special place, situated due south of ...
There is good anchoring in Cowichan Bay and nearby, and salt water enough to make any boater happy. ...
We’re gliding through green-blue waters, colours so vivid and bright they hurt your eyes. We’re set ...
The Halifax waterfront has been attracting more and more large yachts in recent years. However, a ...

Moorings In BrazilWith an increasing amount of interest in South America as a charter destination, The Moorings has responded with a new base in Paraty, Brazil. Surrounded by towering jungles plummeting into the waters of Baia Carioca, this charter cruising region features bays peppered with islands and world-famous beaches.

Centrally located between Rio de Janeiro and São Paulo, Paraty (pronounced “Para-chee”) holds the key to many natural wonders you can only discover by boat.

Read more about Moorings' Brazil Charters......................

 

Marine Products

  • Prev
It is not often I get to drive the newer model of something I own. Most of the time the model I own ...
Good news cruisers, it’s coming in early Summer 2020 – PORTS Rideau Canal and Lower Ottawa River ...
Few things are as frustrating to a boat owner as being becalmed or running out of fuel—or both. If ...
Every cruiser in the region has used it for years, but now there’s a brand new edition of the ...
When you visit the Toronto Boat Show, come to the Canadian Yachting booth (#1741), trial a pair of ...
With the Davis Scrubbis Underwater Hull Cleaning Kit it's easy to rid a boat of algae, grass, and ...
There is nothing worse for me to have too many keys on your key chain. Even if I move a few to ...
One of the most important boat-ownership tasks is cleaning the bilge. Not only does it reduce ...
Most dock boxes aren't sturdy enough to sit on. Nor are they too comfortable. Finally! - the ...
Too hot to bake? No oven onboard anyway? Try these no-bake shipboard treats. (Yes, we know they’re ...