How Long to Warm Up Your Car in Winter: 30 Seconds, Then Drive Gently

How long to warm up a car in winter? For any fuel-injected car built in roughly the last 35 years, start it, give it about 30 seconds while you buckle up, then drive off gently until the temperature needle moves. That is what the automakers, the Department of Energy and Natural Resources Canada all say, and long idling in the driveway mostly burns gas.

How long should you let your car warm up in winter?

For a modern gasoline car with fuel injection, about 30 seconds of idle is enough before you put it in gear. Fueleconomy.gov, which is run by the Department of Energy and the EPA, says most manufacturers recommend driving off gently after about 30 seconds. Ford has put it more bluntly: don’t idle for more than 30 seconds, because today’s engines don’t need it. A summary of owner’s manuals compiled by Oak Ridge National Laboratory and the East Tennessee Clean Fuels Coalition found the same story across brands. Chevrolet’s guidance in that report says even on the coldest mornings the vehicle is ready to go in 30 seconds. BMW’s manuals tell drivers not to let the engine warm up while the car sits still, and to drive off at moderate engine speed instead because that is the fastest way to reach operating temperature.

Why 30 seconds? Because that is roughly how long it takes for oil pressure to build and get oil to the top of the engine. Consumer Reports’ chief mechanic John Ibbotson puts full lubrication at 20 to 30 seconds on modern engines, and points out that a cold engine idles at 1,200 rpm or more, which helps push oil around quickly. By the time you’ve found your seat belt and your sunglasses, the engine is lubricated. It is not warm yet. But warm and lubricated are two different things, and only one of them matters before you pull out.

The “warm” part happens best while driving under light load. An idling engine makes very little heat because it is barely doing any work. Put it in gear and ask it for 15 or 20 percent throttle at moderate rpm and it makes a lot more heat, so the coolant, the oil, the transmission and the catalytic converter all come up to temperature sooner.

On really bitter mornings, Natural Resources Canada (the folks who have studied this in places where minus 20 is a normal Tuesday) says that in most cases you need no more than 2 to 3 minutes of idling from a cold start in winter. That’s the ceiling, not the target, and it’s mainly about making sure the windows are clear and the engine settles to a steady idle.

Why driving warms the engine faster than idling

Think about where heat comes from. Most of the energy in every gallon of gas leaves as heat, through the tailpipe and the cooling system. At idle, the engine burns very little fuel, so it makes very little heat. Argonne National Laboratory measured idle fuel use on passenger cars at about 0.2 to 0.5 gallons per hour, rising with engine size and idle speed. That’s a trickle compared with what the same engine burns pulling the car down the road.

Argonne also watched catalytic converter temperatures on test cars and found the catalysts warmed much faster when the car was driven than when it idled, on both hot and cold starts. The converter can’t clean up the exhaust until it’s hot, so a long cold idle is a long stretch of the dirtiest exhaust the car will ever make. On the diesel they tested, the catalyst took about 2 minutes longer to warm at 32°F, and when the temperature dropped near 0°F the diesel’s catalyst might never fully warm up at idle at all.

The other half of the story is everything that is not the engine. Your transmission fluid, differential gear oil, wheel bearing grease, power steering fluid, shocks and tires are all cold, and idling in the driveway does almost nothing for them. Natural Resources Canada makes this point directly: wheel bearings, steering, suspension, transmission and tires are best warmed by driving. An automotive instructor at the Northern Alberta Institute of Technology told The Globe and Mail the same thing, adding that you can do real damage by warming the engine for ten minutes and then heading straight out on the highway, because the drivetrain is still full of cold, thick oil. That’s why “drive gently” is the important half of the advice. Thirty seconds of idle, then a few miles of easy driving, beats ten minutes of idle and a hard on-ramp.

What “drive gently” actually means for the first few miles

People hear “drive gently” and picture creeping along at 15 mph. That’s not it. You want normal, unhurried driving that keeps the engine working a little but never working hard. In practice, I use these rules on any cold engine:

1. Start the engine and let it run while you buckle up, set the defrost and check that the windows are clear. That’s your 30 seconds.
2. Pull away with light throttle and short-shift if you have a manual. Keep revs under about half of redline until the temperature gauge starts to move. Several performance cars, the Corvette and BMW M cars among them, actually show a lower redline on the tach until the engine warms, which tells you how the engineers feel about it.
3. Avoid full-throttle, heavy towing and high-speed highway merges for the first few miles. If your commute starts with an on-ramp, take a lap of the neighborhood first.
4. Don’t sit at a high fast-idle with the transmission in gear and your foot on the brake for minutes at a time. If you’re stuck, that’s fine, but don’t do it on purpose to “warm up.”
5. Once the needle is in its normal spot, drive normally. The transmission and axle will take longer than the engine to fully warm, so keep it civil for a few more miles if it’s well below freezing.

Is idling bad for your engine in cold weather?

A few minutes won’t hurt anything. Long, regular idling is a different matter, and the problem is the oil.

When an engine runs cold, fuel doesn’t vaporize completely. Some of it condenses on the cold cylinder walls, slips past the rings and ends up in the crankcase. Water from combustion does the same thing. Once the oil gets hot enough, most of that fuel and water evaporates and leaves through the PCV system. An engine that idles cold for a long time, or only ever makes short trips, never gets the oil hot enough to cook that stuff out. The ORNL owner’s-manual summary notes that many automakers warn extended idling can contaminate the oil and shorten its life. One manufacturer’s service alert filed with NHTSA spells out what happens on direct-injection engines: on repeated short trips where the engine never reaches normal operating temperature, fuel gets into the oil, the oil level actually rises, and it can’t evaporate until the car finally takes a longer drive.

Fuel-diluted oil is thinner than it should be, and that’s the opposite of what you want protecting your bearings. If you see the dipstick creeping above the full mark in winter and smell gas on it, that’s what you’re looking at. The fix is a real drive of 20 minutes or more now and then, and following the severe-service oil change interval in your manual if your driving is mostly short hops in the cold. For winter oil, run the viscosity your manual calls for, and in a cold climate the lower “W” number matters more than the brand on the bottle.

How much gas does idling to warm up your car waste?

Less per morning than you might think, more per winter than you’d like. Here are the published numbers:

Measure	Figure	Source
Passenger car idle fuel use	0.2 to 0.5 gal per hour	Argonne National Laboratory
10 minutes of idling	0.25 to 0.50 L of fuel, 600 to 1,200 g of CO2	Natural Resources Canada
15 minutes in a drive-through	About a quarter gallon	Chevrolet guidance, ORNL manual summary
Idle vs restart break-even	About 10 seconds	U.S. Department of Energy
Winter mileage hit at 20°F vs 77°F	About 15% (up to 24% on 3 to 4 mile trips)	fueleconomy.gov
Block heater benefit at minus 20°C	Up to 10% better fuel economy	Natural Resources Canada

Run those numbers on a typical 10-minute remote-start warm-up, five mornings a week through a four-month winter, and Argonne’s 0.2 to 0.5 gallon-per-hour idle rates work out to roughly 0.7 to 1.75 gallons a month, more on a big V8 truck. Argonne estimated that if every car in the country idled just 6 minutes a day, it would waste about 3 billion gallons of fuel a year. That’s the cost side. On top of it, cold weather already hurts mileage: fueleconomy.gov says a conventional gas car gets roughly 15 percent worse mileage at 20°F than at 77°F, and as much as 24 percent worse on short trips of 3 to 4 miles. Idling only makes the short-trip number worse, because you’re spending fuel to cover zero miles.

There’s a cheaper way to start with a warm engine, which brings us to block heaters.

When should you use a block heater, and for how long?

If you live where it regularly drops well below zero, a block heater is the single best warm-up tool you can own. It’s a small electric element (most commonly in a core plug hole in the block, though some heat the oil pan or sit in a lower radiator hose) that warms the coolant overnight, which in turn warms the block and the oil.

Natural Resources Canada says that at minus 20°C (minus 4°F), a block heater can improve overall fuel economy by as much as 10 percent, and for a single short trip at minus 25°C (minus 13°F) the saving can be around 25 percent. You don’t need to leave it plugged in all night. NRCan recommends a timer that switches it on about two hours before you drive; the Canadian Automobile Association has suggested a bit longer, 3 to 4 hours, according to The Globe and Mail. Outdoor plug-in timers are cheap and pay for themselves fast.

When is it worth plugging in? The NAIT instructor quoted by The Globe and Mail draws the line at about minus 15°C, which is 5°F. Above that, the gain is small and you’re mostly paying for electricity. Below it, oil thickens to the point that the engine works noticeably harder to crank and pump oil, and the block heater earns its keep.

Even after plugging in, you still only need the same short idle. A warm block doesn’t change the fact that the transmission and axle are cold.

Should you use a remote start to warm up your car?

A remote starter is a comfort tool, not an engine-health tool. There’s nothing wrong with starting the car a couple of minutes early so the windshield clears and the seat isn’t an ice block. The trouble is that it’s easy to hit the button and then finish your coffee, and suddenly the car has idled for 15 minutes. NRCan’s guidance is to start the vehicle shortly before you’re ready to drive away, not long before. Argonne’s own idling handout makes the same point about not overdoing a 10-minute remote warm-up, because that is still idling and neither the engine nor the catalyst is at its best temperature.

Two other things to keep in mind. First, some cities and states have anti-idling rules, and leaving a running car unattended is illegal in some jurisdictions, so check your local rules before you make a habit of it. Second, never remote start a car in a closed garage. Carbon monoxide builds up fast, and an attached garage shares air with the house.

Do you need to clear the windows before driving?

Yes, and this is the one legitimate reason to idle longer than 30 seconds. Driving with a peephole scraped in the frost is the most dangerous thing anybody does on a winter morning. NRCan’s advice to keep idling to 2 or 3 minutes comes with the reminder to make sure your windows are free of ice and snow before you go. A good scraper and a brush will clear a windshield faster than any defroster can melt it, so scrape while the engine idles and then go. Clean the snow off the roof too, so it doesn’t slide down over the windshield at the first stop sign or blow back onto the car behind you.

Set the defroster to fresh air, not recirculate, and turn on the A/C if your car allows it with defrost (most modern cars do this automatically). The A/C dries the air, and dry air clears fog off the inside of the glass much faster than humid recirculated air does.

Does a carbureted classic car need a longer warm-up?

This is where the old-timers are right. A carbureted engine really does need a few minutes before it drives well, and the reason is fuel delivery, not oil.

A carburetor meters fuel by airflow, and cold gasoline doesn’t atomize well. When the intake manifold is cold, much of the fuel condenses on the walls of the manifold instead of staying in the air stream, so the cylinders get a lean mixture even though the carb is pouring in plenty of gas. That’s why carbureted cars hesitate, stumble and even stall when you drive off cold. The choke and the fast idle cam are there to fix that. The choke richens the mixture, and the fast idle cam holds the throttle open a bit so the engine doesn’t die. As the engine and manifold warm, the choke opens and the idle comes down. AAA’s Robert Sinclair made the same distinction when asked about warm-ups: older vehicles with carburetors usually need to warm up, while fuel injection has been standard on nearly all engines since the late 1980s and early 1990s. (Fuel injection fixed this because it sprays fuel at pressure, right at the port or into the cylinder, and the computer adds fuel as needed when it sees a cold coolant sensor.)

So for a carbureted classic, here’s what works:

1. Before starting a cold engine with an automatic choke, press the gas pedal to the floor once and release it. That sets the choke and the fast idle cam. Don’t pump it repeatedly or you’ll flood it.
2. Start it and let it run on the fast idle until it will idle without stumbling. On most healthy small blocks that’s a minute or two in cold weather, longer in sub-zero cold.
3. Tap the throttle to kick the fast idle down a step once it’s running smoothly, and see if it holds a steady idle.
4. Drive off gently once it pulls away without hesitation. The choke will keep coming off as you drive.
5. If it needs five minutes or more of idling before it’ll drive at all, something is off. Usually it’s a choke that’s set too lean or sticking, a vacuum leak, or a heat riser valve that’s stuck.

If you’re fighting a cold stumble, start with the choke and idle settings; our guide to setting Quadrajet idle mixture screws and the choke walks through it on the most common GM carb. I’ll admit a soft spot here. I think the small-block 350 is the greatest engine GM ever built, and a good one with a properly set choke fires up on a frosty morning, settles down in a minute or so and drives off clean. When one doesn’t, it’s telling you something needs adjusting.

One more classic-car note: older engines often run plain green coolant, and winter is when a weak mix shows up as a cracked block. Test your freeze protection with a cheap hydrometer before the first hard freeze, and don’t mix coolant types blindly. Our post on Dex-Cool and mixing it with green antifreeze covers why.

How long should you warm up a diesel in winter?

Diesels are the exception that needs a little more patience, especially older ones. A diesel makes even less heat at idle than a gas engine, and as Argonne found, its catalyst may never fully warm up idling near 0°F. That’s the real argument against long diesel idling, along with fuel dilution and soot.

The practical approach for a diesel pickup:

• Wait for the glow plug or intake heater light to go out before cranking. In real cold it may cycle more than once.
• Let it idle a minute or two until the idle smooths out, then drive gently with light loads.
• Plug in the block heater whenever it’s below freezing.
• If you must idle for a long time (a work site, say), use a high-idle feature if your truck has one rather than letting it sit at base idle, and check your owner’s manual for the maker’s specific guidance.

Why does my car take so long to warm up?

If your heater takes 15 or 20 minutes of driving to blow warm, or the temperature needle never quite gets to the middle on the highway, the most likely culprit is a thermostat stuck open. A thermostat that won’t close lets coolant run through the radiator from the moment you start, so the engine can’t build heat in cold weather. It’s a cheap part, and on most engines it’s an easy job. Low coolant can cause the same symptom by leaving an air pocket around the temperature sensor or heater core, so check the level with the engine cold before you buy anything.

A thermostat stuck open isn’t harmless. The engine control computer keeps the mixture rich while it thinks the engine is cold, mileage drops, and the oil never gets hot enough to boil off the fuel and water we talked about earlier. On some cars it’ll eventually set a check engine light for coolant temperature taking too long to rise. On a classic, it just means a cold cabin and more choke time.

If the engine is cranking slowly on cold mornings, that’s a battery problem rather than a warm-up problem. A battery loses a big chunk of its cranking ability in the cold, so read our signs you need a new car battery before you’re stuck in a parking lot.

FAQ

Do cars need to be warmed up at all?

A fuel-injected car needs about 30 seconds for oil to reach the top of the engine, and that is it. The rest of the warm-up happens best on the road under light load. Carbureted engines and diesels are the exceptions covered above.

How do you warm up a car faster?

Drive it gently instead of idling it, and plug in a block heater on a timer when it is below about 5°F. Idling makes very little heat because the engine is doing almost no work.

Should you warm up your car before driving in cold weather?

Only long enough to clear every window and let the idle settle, which is the 2 to 3 minute ceiling NRCan gives for real cold. If the car takes far longer than a short commute to warm, check the thermostat.

Winter also asks a lot of your tires, and no warm-up routine helps if the car can’t stop. If you’re still on all-seasons, look at our guide to the best tires for driving on ice and the more general DIY maintenance basics worth doing before the snow flies.

Sources

• fueleconomy.gov (DOE/EPA): Fuel Economy in Cold Weather
• ORNL / East Tennessee Clean Fuels: Summary of OEM Idling Recommendations from Owner’s Manuals
• Argonne National Laboratory: To Idle or Not To Idle (handout)
• Argonne National Laboratory: Idle, or Stop and Restart?
• U.S. DOE Fact of the Week #1239: idling 10 seconds vs restarting
• Natural Resources Canada: Winter Driving Tips
• Natural Resources Canada: Block Heaters Save Fuel
• The Globe and Mail: Should I still be plugging in my car?
• Consumer Reports: Should You Warm Up Your Car Before Driving?
• Fox Weather / AAA (Robert Sinclair): How long do you need to warm up your car?
• NHTSA-filed manufacturer service alert: oil dilution on short trips (direct injection)

Photo credits (Wikimedia Commons): frost on a car windshield by Famartin, CC BY-SA 4.0. Car coolant temperature gauge by Santeri Viinamäki, CC BY-SA 4.0. Snowed-in cars by Mike McBey, CC BY 2.0. Images resized by CarNutChronicles.

Note To Reader: Car Nut Chronicles is reader supported. We may post content which contains links to affiliate sites such as Amazon where we may earn a small commission. This helps us keep the lights on and the articles you enjoy being produced. Thank you for your readership, we appreciate you!