Every year, the debate opens up about whether or not we should let our cars warm up before driving them in colder weather. Many people start up their cars and let them idle for a few minutes while they go inside for coffee. Then they wait for the defroster to deice the windshield and the heater to warm up the interior of the car before they get back in and drive away.
There are videos that warn of potential engine damage as well as the wastefulness of this routine, and while the videos do make some valid points I also think that they are a bit overly dramatic and go about delivering the message inaccurately. Should you let your car warm up before driving away? Because the spectrum is so broad that it can’t address every vehicle on the road, the answer requires some explanation.
In order to explain what I mean, let’s take a trip back in time to where this routine started. Let’s go back to the mid 20th Century, before all cars had EFI.
Choking Off The Carburetor
During the mid to late 20th century, we let our cars warm up in colder weather because we essentially had little choice. Most cars had carburetors, and they were a bit unforgiving when it was really cold outside.
I remember cold Maryland mornings when it took a couple of tries to get the car started; there was a routine many of us went through during the winter months. We needed to set the choke before we started the car, and sometimes that alone wasn’t enough.
But rather than letting the car sit and idle for ten minutes, I scraped the windshield if I had to, then got back in the car and gave it a little gas to get the oil circulating more.
When I got in my car, I pressed the gas pedal once or twice. This was to squirt some fuel into the intake, and also to activate the choke (or I pulled a lever for a manual choke). That closed off much of the cold, incoming air to the carburetor and it set the carburetor to what we called “fast idle.” The throttle lever was locked at a higher idle speed and it kept the throttle blades open slightly more until the car got warmer and the choke could be released.
But rather than letting the car sit and idle for ten minutes, I scraped the windshield if I had to, then got back in the car and gave it a little gas to generate some heat and get the oil circulating more. Once the car warmed up a little bit and would stay running, I would give it one blip of the throttle to release the choke and I drove off. All in all, this was a couple of minutes, not really long enough for a cup of Joe. Obviously, if your vision is impaired by ice or frost, don’t drive until you can do so safely.
Steve Brule, from Westech Performance, gave us a very simple rule about warming up the engine. “The bottom line is that the car needs to be warm enough to drive,” he said. “But realistically, letting the car idle for ten minutes is a tremendous waste of fuel.”
Driving In Colder Weather
In the ’60s and ’70s, we could still drive our cars when it was cold outside, but when it was extremely cold the fuel couldn’t atomize completely until the intake temperatures warmed up a bit. Cold air is much more dense than warm air.
If we romped on the gas pedal when it was cold, the car would typically sputter, or even stall. Even if the choke was adjusted properly, if the temperature was too cold, it was simply best to let the engine get a little warmer before driving away.
The thing about a carburetor is that an accelerator pump doesn’t change the amount of fuel just because the engine is hot or cold. -Steve Brule, Westech Performance
When EFI entered the scene, fuel delivery was quite different. Unlike a carburetor, when you press the throttle, the various sensors tell the computer how much fuel to squirt, and what the air/fuel ratio (A/FR) was, and compensated accordingly.
“The thing about a carburetor is that an accelerator pump doesn’t change the amount of fuel just because the engine is hot or cold,” Brule said. “With fuel injection, the system is so sophisticated it can make adjustments that a carburetor can’t make.”
Warming Up Your Car Doesn’t Take Ten Minutes
The videos state that the enriched fuel mixture when an engine is cold can remove oil from cylinder walls and cause damage to your engine. While that is true to a point, it’s such a minimal amount that Brule said he doesn’t even know if there is testing to prove that it actually can cause long term damage.
Warming up your engine is subjective, and often times people relate that to whether they are warm or not, and that’s not how you measure your engine’s temperature. There’s a big difference in this process between carburetors and fuel injection, too. Brule said, “No carbed engine is going to run perfect at 10 degrees, it needs to be warmed up. But warming up doesn’t mean it has to be at operating temperature before you can drive it.” Brule suggested driving the car to help that process happen quicker.
If you have a newer, fuel injected car then warming up your car for 10+ minutes is simply wasting fuel. It’s good to let the engine warm up a little to get the oil flowing, because oil will change viscosity once it warms up. But that warming up can come much quicker than ten minutes of idling.
Once the car is running, the amount of time it takes to put on your seatbelt is enough to start driving. -Steve Brule
You can actually warm up the car quicker while driving because a slight load on the engine will produce more heat. Brule said, “Once the car is running, the amount of time it takes to put on your seatbelt is enough to start driving.”
But if you’ve got an older car with a carburetor, a bigger cam, or boost, you might want to let it get a little warmer before driving off, and you can do that by varying engine rpm. Brule stated that letting the car run for a few minutes at 800 RPM is not good for a performance engine. Pressing the gas a couple times until it idles good on its own, and then slowly driving off is completely acceptable. You don’t have to wait until you see the needle move off of the “C”.
One reason that this is true with modern cars is that today’s engines and oils are much more sophisticated than they were decades ago. While I can agree on the portion of the video stating it’s a waste of fuel, I feel the rest is there to bait viewers and to get a dialog started – or even an argument. I simply would rather explain why we used to do this, and why you don’t really need to anymore, and let you make your own decision. Again, because it seems to be a misunderstanding, I’m only referring to situations where you can see clearly through the windshield.
Snow, Ice, Defrosters, Mittens
In sub-freezing temperatures – especially with snow and ice on the roads and on your windshield – it’s never wise to try to drive until you can do so safely, and your vehicle doesn’t stall when you press the throttle. That holds true for any vehicle in any condition. With a carburetor, if just pulling out of your driveway causes your engine to cough and shut off, then it’s simply not safe to be driving until the engine warms up a bit more.
If it is just cold outside, it really isn’t necessary to let your car idle for several minutes to warm up. Letting your car idle so the defroster will melt the ice is simply not a good idea, and you should use an ice scraper to remove ice and snow, not your defroster. That doesn’t mean drive away when you can’t see through the windshield, it just means you should scrape the ice and snow manually when you can.
By all means, if you’re sitting behind the wheel and shivering so bad that you can’t function, wear a jacket and mittens to keep yourself warm. But don’t start your car and then run back inside for some hot cocoa.
There are laws in some states regarding this process, and in some states the authorities can and will write you a ticket for letting your car idle for extended periods of time while you’re inside waiting. While that does have more to do with your keys being in an unattended running vehicle, remote starting will help you avoid a ticket. There are even ordinances being enacted with environmental impact studies on this practice of idling for long periods of time.
As the Counting Crows said in Long December: “I guess the winter makes you laugh a little slower, Makes you talk a little lower.” Only someone who grew up in a colder climate can appreciate that verse, for the rest of you who rarely ever see temperatures below 50 degrees, stop wasting fuel, just get in your car, let it run for a few seconds, then go. You’ll be perfectly fine.
Now, if you’re driving across the Arctic circle in a classic car with a factory Quadrajet and you stop overnight on your way to visit Santa, you’re on your own. We can’t help you there.