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

Video Gallery

 

 

Beneteau Oceanis Yacht 54By Zuzana Prochazka

Beneteau saw an opportunity to add a little thrill to any cruising adventure, so they took the hull of the First 53 racer (introduced just last year), and with a few fashionable changes, created the Oceanis Yacht 54, the new entry-level of Beneteau’s swanky Oceanis Yacht line. The result is a performance cruiser that sails like a witch and looks like a grande dame.

Design

Roberto Biscontini is the naval architect and Lorenzo Argento created the details of the exterior and interior design. 

Read More

Destinations

  • Prev
Over the course of four days in September 1864, representatives from Prince Edward Island, Nova ...
The new owners of L’Orignal Marina offer boaters a new destination. Located in a charming ...
Commemorating 100 (+1) years of through-navigation on the Trent-Severn Waterway National Historic ...
On Friday, April 2 at 7 pm ET on TVO and streaming anytime after that on tvo.org and the TVO ...
Salt Spring Island, the largest among the Gulf Islands, has a certain mystique—much of it having to ...
Located in Lake Huron, the internationally significant Manitoulin Island is the largest freshwater ...
In Part I, Sheryl Shard ended the story at June and the start of Hurricane Season when they were ...
You likely aren’t quite ready to travel yet, but we have our fingers crossed that we can all fly ...

Riverest MarinaThe new owners of L’Orignal Marina offer boaters a new destination. Located in a charming francophone village in Eastern Ontario, this joined marina and restaurant venue is the ambitious initiative of long-time entrepreneur André Chabot and biologist Alexandra Quester, both residents of L’Orignal.

The purchase of the L’Orignal Marina was made official in November 2020. The new year was barely underway when all 50 available slips were already reserved. No wonder the addition of member and visitor slips is already planned for the 2022 season – the 2021 count is up to 62 power and sail already. At the moment, the Riverest Marina offers boaters a stop where they can launch their boat...

Read More

Lifestyle

  • Prev
Photograph taken on Sept 15 while drifting home after the last Wednesday evening race at Collins ...
On the afternoon of Sunday, October 3, fourteen exceptional sailors were inducted into the Canadian ...
My husband and I purchased this beauty in Gananoque two weeks ago and boated it from there across ...
Last issue we featured a story about the engagement proposal aboard Via-Mara, a 1969 Trojan 42 Aft ...
With thanks to Sail Canada, here’s a collection of photos that are Olympic quality. Clearly our ...
Wow. That was a lot of fun reading the collection of boat names that came in from all over the ...
No individual had a greater impact on the modern sport of sailing than Bruce Kirby. Known and ...
Just off The Ocean Race European Tour, Daniel is setting his sights on competing in The Ocean Race ...
After being our fearless leader and publisher since CYOB kicked off, Greg Nicoll, handed over the ...
Swim Drink Fish is spearheading the Vancouver Plastic Cleanup by installing, maintaining, and ...

Marine Products

  • Prev
Dockmate®, manufacturer of advanced wireless remote controls for yachts, has announced expanded ...
PORTS Guides are The Essential Boating Companion and Look Great in Gift Wrap!    
Updated features and benefits offer next level of product excellence by integrating innovative ...
AkzoNobel Yacht Coatings has introduced a new, easier to apply topside system with two new products ...
Whether for news, weather or just to watch the game, onboard television reception is important. But ...
Kanvaslight® was specifically engineered for a long life in a salty, sun-drenched environment. The ...
Watermakers take ocean water and create perfect drinking water using reverse osmosis. A Schenker ...
If you’re headed out for a weekend afloat or on a week-long cruise you often must park your vehicle ...
Ten years ago, St. Margaret’s Bay (Halifax), Nova Scotia-based SailTimer Inc. made the first ...
Between the odor and working in confined spaces, replacing an onboard sanitation line is never a ...

News

  • Prev
According to digital news outlet www.insuaga.com, a new, full-service and modern Port Credit marina ...
The Canadian Sailing Hall of Fame and the Marine Museum of the Great Lakes at Kingston are pleased ...
Paul Tennyson adapted from the reinforced plastics business to form Canadian Sailcraft in 1963. ...
Canadian sailors Antonia and Georgia Lewin-LaFrance from Chester NS won the bronze medal at the ...
Royal Canadian Yacht Club’s Defiant completed a six-race sweep of the Cup for Canada over Zing, the ...
On September 6, Groupe Beneteau laid out its course to develop new boating experiences, new ...
Last Friday, the first ever Canada’s Celebration of Sailing honoured the season for Sailing in ...
Boating Ontario is very proud to have Transport Canada’s Office of Boating Safety jump on ...
Montreal-based Vision Marine Technologies, Inc. is headed to the Lake of the Ozarks Shootout to ...
Summer is in full swing with Canadians enjoying time outside and on the water. So, while enjoying ...

Mia and Caleb's EngagementOn July 23 last year, CYOB published a piece on a beautifully restored 1967 Trojan 42 Motor Yacht in Oromocto NB. (That piece was also expanded in CY magazine later in the year.)

One of our Canadian Yachting contributors, Denise Miller, had shared the article on my social media and a young man reached out and asked if she could connect him with the owners of the boat, Dave and Barb. Denise leapt into action and Dave and Barb were thrilled. They concocted a plan that the young lady, Mia, thought she was coming to model for a sales brochure for Dave to do charter tours.

Read More