Aug 13, 2020

Merc thermostatA thermostat housing on the front on a Mercruiser engine

July and August  in Canada are the months of boating. People are on the water – exploring, cruising, fishing, voyaging  and racing. Maintenance and repairs aren’t the priority – the fun is.

Nothing ruins the fun faster than watching the temperature gauge on your engine rise and not come down. Fear and anxiety mix – forefront in your thoughts will be “How do I get safely back to dock?”, followed quickly by ‘How bad is the damage, and how much will it cost?’

The next day, my phone rings: ‘I need a new impeller’.  But 99% of the time, the impeller hasn’t been removed or inspected to determine whether it should be replaced.

Lets pause for a moment, in an effort to understand rather than assume. Let’s look at the whole system, and diagnose an overheat methodically.

 stern drive diagramA diagram showing the pick-up and impeller locations on a Mercury Alpha stern-drive unit

At the surface level, the cooling system is really simple, and it functions essentially the same way in inboards, stern-drives and outboards: water surrounding the boat enters the engine via a through-hull or through the pick-up in the stern-drive unit or the outboard.

Water is sucked up into the engine via the turning of an impeller – a series of vanes working much like a paddle-wheel. Water is then pushed through the lower part of the engine, past critical areas. When the engine is still warming up, much of this water is forced through the engine and then out through the exhaust, into the lake/ocean. As the engine’s temperature rises, the engine’s thermostat opens and allows water to flow through other parts of the engine. The engine will cool slightly, the thermostat will close until the temperature rises again.

The cooling water runs via rubber hoses, through pumps, impeller housings, small passages in the heart of the engine, then out through exhaust ports and rubber boots. There’s lots of places for the things to go wrong. Here’s a few:

  • A blockage in the pick-up.
  • Pick-ups aren’t underwater.
  • The seacocks are closed.
  • Hose leaks.
  • The impeller is worn.
  • The thermostat is blocked.
  • Hoses are blocked.
  • Broken Belts.
  • Damaged circulation pump.

 blown head gasketA blown head gasket due to an overheat

As you can see – a comprehensive list. A mechanic will work their way through the system methodically, from pick-up to the exhaust, exploring each part of the system in turn until they discover the cause. Sometimes this involves flushing the engine with water, or using clear hoses to watch the water flow through each section.

If you see the temperature rise, slow the engine down if safely possible. An engine running at slower speeds has less friction, producing less heat. Try to determine why the engine is overheating: is there a blockage that can be fixed on the water? Or, is water not flowing because of a damaged impeller or pump?

A few rules of thumb:

  • If water is flowing OUT of the engine, then it must be flowing IN. Check the exhaust for water flow
  • You have to see or feel water to know if it’s flowing. Feel the hoses – they should be cold as seawater flows through them. If you can’t tell, remove hoses and replace them with clear hoses to watch where/how water moves
  • Impellers are relatively cheap, but getting to them can be tough. Before buying an impeller, make sure that a replacement is needed, and that you have a plan to take care of it
  • If your engine has overheated, have the engine checked over. Depending on the severity, an overheated engine can cause hoses, sensors, wires and boots to melt. They can even cause metal components to warp, necessitating costly rebuilds.
  • Keep your temperature gauge in working order, and keep a close eye on it when the engine is running.

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

Boat Reviews

  • Prev
What perfect timing! Beneteau is has just announced their new Antares 11 model for North America ...
Commodore’s Boats is a full-service shipyard with over 50 years of generational history and ...
The Oceanis Yacht 54, younger sister of the Oceanis 62, embodies the innovation that has always ...
Beneteau announces the launch of the latest addition to the Antares range! With a length overall of ...
I had been looking forward to a sea trial aboard the Greenline 33 because I was hoping it would ...
New at the end of 2019, the 58 Salon Express design features large windows to flood the living ...
No wonder this is one of Regal’s best-selling boats; the Regal 33 Express offers amazing ...
The newest member of Beneteau’s Gran Turismo line is the GT 36 and this yacht brings the style and ...
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 ...

CY Virtual Video Boat Tours

Virtual Boat ToursWe all love boats and nothing can break us up! So, what better way to spend our time than looking at interesting boats and going aboard in a virtual ride or tour. We have asked our friends at various dealers and manufacturers to help us assemble a one-stop online resource to experience some of the most interesting boats on the market today. Where the CY Team has done a review, we connect you to that expert viewpoint. If you can’t go boating, you can almost experience the thrill via your screen. Not quite the same, but we hope you enjoy our fine tour collection.

 

Read more about the CY Virtual Boat Tours....................

 

Beneteau Antares 11By Andy Adams

What perfect timing! Beneteau is has just announced their new Antares 11 model for North America and I think it will be exactly what many people are looking for.

The boat business has simply taken off during 2020, spurred on by the social distancing requirements of the global battle with COVID-19. In many regards, this situation has brought a lot of families closer because there are few options for travel and recreation. I suspect that many families have rediscovered the joys of being together, going places and doing things.

Read More

Destinations

  • Prev
The approach to the Chemainus Municipal Dock from Stuart Channel is straightforward and is ...
I leaned my head back into the water and floated easily. Having spent my childhood playing in ...
History: right after gym and just before chemistry class. Fifty minutes of naming the prime ...
On May 19, the New York State Canal Corporation today announced an updated opening schedule for the ...
If you have four hours to enjoy a fine tour of one of Canada’s most interesting waterways (let’s ...
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 ...

ChemainusBy Marianne Scott

The approach to the Chemainus Municipal Dock from Stuart Channel is straightforward and is protected from all but strong northerly winds. The only obstacle may be some large log booms often anchored in the harbour. The Dock is immediately south of the B.C. ferry terminal; the ferry runs to Thetis- and Penelakut Islands.

Harbourmaster Harmen Bootsma, who has been the cheerful, welcoming presence here for a couple of decades, is ready to catch your lines. 

 

Read More

Lifestyle

  • Prev
Our Photo of the Week (two, in fact) comes from New Zealand where the second America’s Cup AC 75 ...
The Marine Debris Recovery Initiative (MDRI), a collaboration with the Clean Coast, Clean Waters ...
The International Joint Commission (IJC) is reviewing Plan 2014 and could use your help. The plan ...
The Council of the Great Lakes Region (CGLR), thanks to funding from Environment and Climate Change ...
This Photo of the Week came from our own CY Team member Sarah C who, like many of us, is trying to ...
Limestone, a heritage Canadian boat brand that has earned a loyal following over the past 35 ...
Schooner Cove Yacht Club through their staff Capt. and other volunteers organize cruises so members ...
With things the way they are, a whole new batch of Canadians are discovering that boating is IT! ...
Recently while admiring the boats in Victoria Harbour my eyes locked into a 58ft yacht named ...
The 38.1m / 125' motor yacht, custom built in 1930 by Boeing of Canada and last refitted ...

(From left to right) Boating Ontario CEO Rick Layzell; Pollution Probe CEO Christopher Hilkene; NOVA Chemicals VP Rob Thompson; and Council of the Great Lakes Region  President and CEO Mark Fisher

The Council of the Great Lakes Region (CGLR), thanks to funding from Environment and Climate Change Canada, recently announced the launch of the first phase of the Great Lakes Plastic Cleanup initiative with founding partners Pollution Probe, the University of Toronto (U of T) Trash Team, Boating Ontario, PortsToronto, as well as collaborators EnviroPod, Water Products and Solutions-America, Poralu Marine and Georgian Bay Forever.

Read more about the Great Lakes Plastic Cleanup

Marine Products

  • Prev
There are places and things that we read, hear and dream about, that are on our “bucket list” to ...
Almost a year ago to the day, Marquis Yachts re-launched the Marquis brand and introduced the world ...
Every once in a while I test a vehicle that I really find exceptional and this was the case with ...
Tasked with scrubbing non-skid and hardware during frequent routine maintenance, few tools take the ...
Your anchor launch and retrieval  will go a lot smoother if your boat’s bow roller wheels are ...
High quality mooring compensators are essential in line maintenance.      
Knowledge is power—and the Elemen CHIRP Sonar / GPS series from Raymarine gives you the upper hand ...
Balmar has combined recent technology advances to introduce a next generation Battery Monitor. ...
The VITO is the first Lifejacket Harness to include a revolutionary Harness Release System. ...
Incredibly versatile, the Gill's Pilot Jacket is an essential jacket suitable for a multitude of ...