If my 2018 CX-9 sits overnight at around 30°F, will the car’s interior heat up faster if I manually set the fans to max speed and temperature? Or is it better to just set the temperature to max and press the ‘AUTO ON’ button? I’ve noticed the auto mode increases fan speed gradually, but does it actually help?
@Qi
Someone tell this to my mom! She always cranks the thermostat in the house to the max, thinking it’ll heat faster.
@Qi
Same thing with my dad back in the day. He’d always warm the engine first before turning on the heat because he thought it helped the engine heat faster without the coolant running through the heater core.
@Valen
It actually does warm faster that way.
It makes no difference. The interior heat depends on the engine warming up.
Alby said:
It makes no difference. The interior heat depends on the engine warming up.
Can someone explain this to my girlfriend? She always sets it to the highest temp thinking it makes her warmer faster. Thanks!
@Kai
It’s such a simple thing, but people don’t get it. Blowing cold air in your face while waiting for the engine to warm up just makes it worse.
@Kai
My wife does the exact same thing.
@Kai
I tell my spouse this all the time. Would you go home and crank the furnace to max the moment you step inside? No? Then why do it in the car?
When the engine is still cold, blasting the fans to max cools it further, which can slow down how quickly it warms up. Letting the car warm up gradually is usually better.
Adair said:
When the engine is still cold, blasting the fans to max cools it further, which can slow down how quickly it warms up. Letting the car warm up gradually is usually better.
I’m not sure it really makes much difference. While the engine may warm a tiny bit slower with the fans on, that heat still goes to warming the car. It’s not wasted.
Adair said:
When the engine is still cold, blasting the fans to max cools it further, which can slow down how quickly it warms up. Letting the car warm up gradually is usually better.
This makes sense. I always keep my fan on low until the vents start blowing warm air, then I turn it up.
Manually setting it to full fan speed blows cold air until the engine heats up, so you might feel colder instead of warmer. Auto mode waits until there’s warm air before speeding up the fan, which is more comfortable overall. Just set it to your desired temp and let it do its thing.
Other users covered most of this already. Just one important note: keep the auto A/C on. It dehumidifies the air, preventing your windows from fogging up. If it’s off, you could wake up to a frosted windshield inside the car.
@Ari
Also, running the A/C occasionally keeps the compressor in good condition. Turning it off for months at a time can damage it.
If you set the temp to 70°F, it’ll blast the heat full force to get there. Setting it to 80°F won’t make it work harder or heat faster—it just stops at a higher temp.
Wylie said:
If you set the temp to 70°F, it’ll blast the heat full force to get there. Setting it to 80°F won’t make it work harder or heat faster—it just stops at a higher temp.
Cars are smart enough to adjust based on humidity and outside temps. It won’t blast cold air while warming up if you use auto.
@Sky
Fair point, but my main idea is that higher settings don’t make the engine heat up faster.
The quickest way to warm up the car is to start driving slowly if you can. The engine warms faster when it’s working lightly, just like a person warms up with light exercise. Once it’s warm, the cabin heat works better too.
Why not just set the temp to what you actually want? If you want it at 68°F, it’ll get there just as quickly as if you set it to 80°F. The difference is that it stops at 68°F instead of overshooting.