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lou's garage

Thermostats aren’t what they used to be. Gone are the days of the General Motors drop-in style thermostat, where you easily took off a coolant cap, reached down, grabbed a handle, pulled out and replaced an $8 thermostat in 30 seconds.

Now, we have complex units referred to as coolant or thermo modules, thermo control valves (TCV) and in many cases, the common contemporary thermostat is only serviceable as a complete unit incorporating a large plastic housing.

Owners of European vehicles have tolerated these costly units for at least a decade, but the rest of the automotive world is now becoming painfully aware of this newer tech. These units offer finer temperature control using rotary slide valves that direct coolant flow precisely around the engine and are faster at responding to engine load change. The engine will reach ideal operating temperature 50 per cent faster and keep it there over a wider variety of conditions. Whereas a thermostat is a straightforward valve that merely regulates coolant flow, a TCV can be thought of as a mixing valve. The thermostat is now the coolant gate keeper and the TCV is the director.

Case in point is a 2019 Subaru Forrester in the shop this week with a Malfunction Indicator Light (MIL) on, no heat inside the cabin and an engine that won’t easily reach operating temperature. This vehicle has a traditional thermostat, but it also has a TCV that has recently failed, leaving this vehicle with no heat. The vehicle has 70,000 kilometres, putting it just outside of its warranty period, thereby passing this costly repair onto a shocked owner. You would be too if you had just received a quote for a $882 part plus a couple hours of labour.

Why do we need these units when a simple thermostat has done the job previously with very little fanfare? Well, ever-tightening fuel economy regulations have all auto manufacturers scrambling, looking to squeeze every morsel of mileage out of a litre of fuel. This complicated part does exactly that by elevating fuel economy and reducing CO2 emissions approximately 4 per cent. This may not seem like a lot, but manufacturers have no choice in the matter.

This means you have no choice either. The Subaru owner mentioned above is heading in again next week to his local dealer trying to find some financial relief for this repair. In my opinion, 70,000 kilometres seems awful early for such a costly repair to be sprung on an owner, especially when you factor in that up until last week, he had never even heard of a thermo control valve. I suspect this will be a common complaint in years to come for a lot of aging vehicles.


Your automotive questions answered

Hi Lou, I own a 2016 Chevrolet Colorado with 80,000 kilometres on the odometer. It has been a great vehicle for me aside from one issue, a musty odour that occurs when I run the heat or air conditioning.

I took the truck in to my local dealership last summer and for around $200 they sprayed a mould removal product into the chamber that holds the evaporator core. It did work for a few months, but as of a couple weeks ago, the odour is back.

I understand that to replace the unit would require removing the entire dash of the truck and a $2,000-plus repair bill and could result in some unwanted rattles in the dash after reassembly. I’ve also read that pumping ozone through the evaporator core might be an option to kill the mould.

Kind regards,

Kelly T., Lethbridge, Alta.

It is the Styrofoam-like insulation material that surrounds the core that holds your stinky nemesis. Spraying the evaporator core as you have found out is only a temporary solution. This spraying process sees the majority of the product being blown directly into the aluminum fins of the core and very little actually infiltrates the insulation.

The mould exists on the porous material of the insulator and is very difficult to eliminate without actually physically removing the dash and evaporator. If you can’t live with the smell, you have little choice in the proper repair path. The only choice I see is where you get it serviced. While time consuming, it is not a difficult task. I’m sure there are plenty of options outside of the dealer that can save you significantly and offer a rattle-free repair.


I have a 2012 CR-V which I bought “Certified” 2.5 years ago. I have put just under 10,000 kilometres on it since then. At the end of the first year, it began to clunk into R from P when the vehicle is parked on any sort of incline. It doesn’t always happen, but does the majority of time. This doesn’t occur on a level surface. I understand that there is a pawl which engages a notched plate to hold the transmission output shaft from turning while parked. Could it be anything to do with its disengagement? The brakes are always firmly applied so there should be no gravitational load on the transmission via the wheels. The transmission fluid is properly topped up. Any ideas?

J. P.

I have two thoughts and they both involve the parking brake. First, is it possible that your parking brake is not operating properly? You may think it is fully engaged, but it could be in need of repair and is not holding the vehicle properly, allowing the vehicle to slip backward slowly over time.

The other thought still relates to the parking brake. When I was taught to drive decades ago, I was instructed to pull into my parking spot, engage the parking brake and then put the vehicle into park, thereby ensuring the parking brake was doing the bulk of the work to hold the vehicle stationary and not the transmission. Most drivers, however, arrive at their parking spot, throw it into park and then as an afterthought engage the parking brake, if they engage it at all. Small difference but might be important in your case as one way relieves the vehicle weight being held by the transmission and one does not.

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.

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