Why does the car heater take so long to get warm?
The pleasure of driving a cold car on a snowy morning starts when the heater starts working. How long should it normally take for a heater to get warm in cold weather? It depends on the outside temperature and on the car you have.
Winter in Canada.
Modern cars have smaller fuel-efficient engines that burn less fuel and, as a result, generate less heat. Older cars with larger engines were burning more fuel, but they were warming up faster.
If you have a late-model car or SUV with a 4-cylinder engine, and it is parked outside in below-freezing temperatures, it may take up to 10-15 minutes of driving before you can get good heat from the vents. An older car with a larger engine may take 5-10 minutes of driving to warm up. The engine warms up faster under load, when it burns more fuel, for example, when driving uphill. Turning the rear window defogger or heated seats also adds load on the engine and helps it warm up faster. On the other hand, running the heater (blower motor) at full speed from the start cools the engine down and causes it to take more time to warm up.
If it takes longer than normal before the air from the vents becomes warm, there are several things that need to be checked, but first let's see how the heating system works:
How the heating system works in the car:
The heating system in a car with a gasoline or diesel engine uses heat from the engine to warm up the cabin.
Engine cooling and cabin heating (HVAC) system in a car.
There is a heat exchanger called a heater core
built inside the vehicle HVAC system (see the illustration). The heater core is a small 'radiator' that is connected to the engine cooling system.
The cooling system of an engine is filled with liquid coolant that circulates between the engine and the main vehicle radiator. The part called a water pump
creates the flow of coolant within the system. The thermostat valve blocks the circulation through the main radiator when the engine is cold; it opens when the engine reaches the specified temperature. See the photo of the water pump and thermostat
. Read more about the water pump
As the engine is warming up, hot coolant starts flowing through the heat exchanger (heater core).
Air flow in the HVAC system of a car.
The blower motor of the HVAC system creates the air flow. The air flows through the A/C condencer and then through the heater core; see the illustration. Various ducts and doors inside the HVAC system distribute the warm air to the vents. The door that controls the mix of warm and cold air is referred to as a the temperature blend door
. Doors that direct the air flow to different vents are called mode doors
What needs to be checked:
If there is not enough heat, the first thing to check is the coolant level in the overflow bottle. If it's low, the coolant must be topped up and the cooling system must be checked for leaks.
Normally, the coolant level should be between Min and Max marks in the coolant expansion bottle.
If you want to top up the coolant yourself, don't open the cooling system cap when the engine is hot as the coolant is under pressure. Check the precautions and instructions on how to do it in the owner's manual. Dealership mechanics typically top up the coolant in the overflow bottle during regular oil changes.
The coolant density also needs to be measured. If the density is not within specs or the coolant appears dirty in the expansion bottle, your mechanic may recommend flushing the cooling system, as the heater core could be partially clogged up. This problem is not uncommon in older high-mileage cars. Flushing a cooling system in a car costs from $140 to $250.
A thermostat that is stuck open can also cause long warm up time, however, in most cars, the Check Engine light comes on if the thermostat is stuck open.
Checking coolant density.
Another symptom of a stuck-open thermostat is when the engine temperature drops below normal when driving on a highway.
In some cars, if the temperature blend door inside the HVAC system is not functioning correctly, it can also cause a lack of heat from the vents. Often, an electrical actuator or parts of the cable mechanism in the manual HVAC system wear out, causing the blend door not to close off the cold air completely. In case of a manual heater control, it may feel like the hot/cold knob is jamming and not moving all the way to "Hot".
If there is a lack of air flow from the vents even at full blower motor speed, the cabin filter must be checked. A dirty cabin filter can restrict the air flow in the HVAC system.
However, if the heater works well after the car warms up, including when driving on the highway and when the car is stopped at a red light, it's unlikely that your mechanic will find any problems.
Ways to warm up your car faster in winter
One of the possible solutions is a remote engine start.
Remote engine start.
You start your car from the comfort of your home and it is warming up for you. Typically a remote engine start is programmed to run the engine for a few minutes and then shut down automatically. It might also be set to shut down if someone opens the door in a car.
If the vehicle doesn't have a remote engine start from the factory, installing an aftermarket remote engine start at a local car electronics installer shop will cost from $280 to $580. Of course, the car will use some fuel and produce emissions while warming up. In some jurisdictions, leaving a vehicle unattended while the engine is running is illegal. Check your local laws.
As an alternative, some people in the Northern U.S. and Canada opt to install an engine block heater. It's an electrical heater that plugs into a household power outlet. Installing a block heater costs $320-$580 for an average car. Many people use a block heater with a suitable heavy-duty programmable power outlet timer: you can program the block heater to turn on a few minutes before you are leaving in the morning. The block heater warms the coolant inside the engine so it won't take long to get warm air from the vents once the engine is started. This option is more environmentally friendly, since you are only using electric power. The downside is that a block heater requires a power cord to be connected to the car.
Another option is to run the engine for a while before driving off.
This brings us to the question many people ask:
What is better for the engine in cold weather: driving the car right away or letting the engine warm up first? From a technical point of view, as long as the engine is properly maintained and has enough oil, either option is okay, especially if your car uses synthetic oil. If it's extremely cold and the engine has old mineral oil, then it's not a bad idea to warm up the engine for a few minutes before driving.