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
CYOB Inbox
  • 03 December 2019
  • By Ethan

CY Inbox: Love for Ask Andrew

Andrew, I am in St Andrews NB and run an 87 Niagara 35E that I bought in Oakville in 2016. Significantly modified by a previous owner and have to say that I enjoy your contributing articles to the...

Lifestyle

  • Prev
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 ...
Arie and Maribeth sent us this photo from their honeymoon departing Killarney…I think they were in ...
This shot was taken last week by Jessica Lee, a freelance photography pro, Albacore racer and part ...
On a sunny and windless day we led Alicia and another sailboat into New York Harbour. There were ...

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 ...

J99By Katherine Stone

All set to pull out the Code 0 before dousing the jib.

It was a very cold and wet beginning to the summer and we never thought it would arrive in Southern Ontario. Doing a 100 miler race on Lake Ontario (billed as the COOLEST race on the lake) with my 8 layers of thermal clothing, woolen ski toque and ski mittens, along with a neck warmer kept me on the edge all night, just out of frostbite reach. I shouldn’t have complained, as we also had wind!

July and August arrived, and it has certainly warmed up, in fact, its too warm, AND we don’t have wind. We are now counting 5 Wednesday nights in a row without wind to race. 

Read more about the J99 Offshore Shorthand Speeder.....................

 

Cruisers Yachts 38 GLSBy Andy Adams and John Armstrong

The North American power boat market has begun to see a new trend toward larger day boats for luxurious onboard entertaining and the new Cruisers Yachts 38 GLS is right on trend plus, it brings a different flavour and set of cruising attributes to this market.

The new Cruisers Yachts 38 GLS carries on the styling and accommodation quality of the company's Cantius line of cruising yachts while beginning an entirely new family of day boats. 

 

Read More about Cruisers Yachts..................

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 ...

KingstonBy Amy Hogue

Cruise into the city of Kingston, Ontario, and it will quickly become clear that this city and surrounding waterways have something special. Built around the northern shore of Lake Ontario, Kingston is the place to go if you love to explore new waterways, fantastic views, and exceptional boating opportunities.

Sitting at the intersection of three world-class Canadian bodies of water, Lake Ontario, the St. Lawrence River, and the UNESCO World Heritage Site, the Rideau Canal (Cataraqui River from Kingston to Newboro), the water’s influence is deeply woven into Kingston’s culture and history. 

Read more about Kingston......................

 

Marine Products

  • Prev
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 ...
It is not that often I drive as big a vehicle as the Nissan Armada but I love the nautical name and ...
The new edition of PORTS Cruising Guides: Georgian Bay, Lake Huron & the North Channel from the ...
Canadian Yachting’s Chartering Handbook, full of information and advice for heading off to a ...
Navigating the process of yacht care and maintenance just got a whole lot easier, following the ...
I will be honest, I am generally not a big fan of Sport Utility Vehicles (SUV). My wife and I own ...
The FX model is Yamaha's top-of-the-line three seater WaveRunner and a totally new model for 2019. ...
In the April 2015 edition of CY magazine, I published an article on anchors and anchoring – Staying ...
The Seabin device part of the Oak Bay Marine Group trial, has had promising results so far while ...