Should I warm my car up before I drive?

January 11, 2006 7:51 PM

What are the advantages (if any) of letting your car engine run idle to warm up before driving?

I've noticed a few people in my apartment block are starting their engines in the morning and coming back about 15 mins later. Why are they doing this? Isn't this just a waste of gas and bad for the environment.

posted by xoe26 to Travel & Transportation (18 answers total)

Probably doing it to heat the car's interior before they actually get in and drive. More comfy that way.

But there are several advantages to idly heating up the car when it's really, really cold. You're heating up the oil, getting the coolant flowing, etc.
posted by frogan at 7:53 PM on January 11, 2006

I've heard Click and Clack say that it's unnecessary to warm up modern cars for the purposes of engine health.

But I agree with frogan. In cold climates, in winter, it's common to warm your car up before you get in to leave for work. On frosty/icy/snowy mornings, I sometimes do that to get the defrosters going on the windshield and back window to make it easier to scrape.

To even out my fossil-fuel karma, I always turn off my motor when I get caught at the drawbridge.
posted by Miko at 8:03 PM on January 11, 2006

Here's what the Car Talk guys say, officially.

Unless it's below freezing, cars don't need to be warmed up at all. Driving them gently is the best warm up there is. If it's 25 degrees out, you might want to let it warm up for 30 seconds. If it's 10 degrees out, warm it up for a minute. If it's -10 degrees out, move somewhere warmer.

posted by Miko at 8:15 PM on January 11, 2006

I think that it used to be valid with older (carburetor vs. newer fuel injected) cars. Cars with fuel injectors shouldn't need any significant warming up, providing that the temperature isn't extreme enough to bring the engine block to brittle-inducing coldness... and even then, it'd be prudent to have an engine-block-heater plugged into AC.
posted by PurplePorpoise at 8:20 PM on January 11, 2006

I believe that it's good to let the run run at idle for a few seconds to allow the oil to re-circulate and coat the moving parts of the engine to minimize wear. This was ingrained into me by my father, whose life seemed to be shortend whenever he heard someone who had just started their car racing the engine.
posted by JamesMessick at 8:23 PM on January 11, 2006

What Miko said. Here's what the Canadian environment ministry has to say:

•An idling engine releases twice as many exhaust fumes than a vehicle in motion.
•If every driver in Canada avoided idling for 5 minutes a day, we could prevent 1.6 million tonnes of carbon dioxide from being emitted.
•No more than 30 seconds of idling is needed for oil to circulate through your engine. Many components, such as the wheel bearings, tires and suspension system will only warm up once the vehicle is moving.
•Restarting your car many times has little impact on engine components, adding only around $10 per year to the cost of driving, money that is recovered in fuel savings.
•Ten seconds of idling uses more fuel than restarting the engine.
•Idling can damage your engine since it is not operating at its peak temperature where fuel is completely burned. Fuel residue from incomplete burning can damage engine parts.
•Idling a vehicle for 10 minutes a day uses an average of 100 litres of gas a year. If gas costs 70 cents a litre, you will save $70 per year, just by turning your key.
•During the winter, Canadians idle their vehicles for a combined total of 75 million minutes/day. This is equal to a vehicle idling for 144 years. Although we idle our vehicles about 40% less in summer, we still waste an enormous amount of fuel and money.
•A block heater warms the oil and engine coolant, making it easier to start your vehicle and improving winter fuel economy by as much as 10%.

I see you're in California - you don't see -30 &deg:C (-20 °F) temperatures, but if I know I'm going to be driving in that, I'll plug in the block heater for an hour or so, then start it up and let it idle for not even a minute - driving gets it warm. And to address PurplePorpoise's point, I did the same (minimum idling) with the old (carbureted) '79 T-Bird as I do with the present (fuel-injected) '95 Escort.
posted by hangashore at 8:26 PM on January 11, 2006

To elaborate on Miko's quote, they go on to specify:

Drive gently for the first five minutes or so in the morning. If you live one minute from the freeway, don't floor it on the entrance ramp and jump right into the passing lane. Take it nice and easy.

This has to do with getting the oil heated up so it coats and splashes well. That's the real reason for warming up your car. Also, don't "rev" your car while it's warming up and especially right after you crank it.
posted by deadfather at 8:27 PM on January 11, 2006

I agree with everyone saying 'not' but... I would recommend it if your car has some extra bits powered by or dependent on oil. e.g. variable valve timing (vtec, mivec, vvti etc.) or a turbo. driving gently for 5 mins would probably also take care of it, yeah.
posted by dorian at 8:41 PM on January 11, 2006

Side note: in Minneapolis you can get a ticket for leaving your car running and unlocked on the street.
posted by gimonca at 9:02 PM on January 11, 2006

I know it's not environmentally correct, but I do it to warm the passenger compartment and clear the windows of frost on very cold Chicago mornings (which were around 0 F a few weeks ago). In fact, I had a remote starter installed early this winter just so I could do this. (Hides in shame...)
posted by AstroGuy at 9:04 PM on January 11, 2006

I know that my '99 Blazer says there is no need to warm up the car, and advises against it. The time that the owner's manual advises to drive easily is only a couple of minutes. I believe it's against the law to let your car idle like that in Denver.
posted by teece at 9:13 PM on January 11, 2006

I know that this if off-topic, but cool-down idling for a minute or three is necessary on most turbo vehicles, including diesels. The reason is that the turbo bearing has engine oil running through it; at operating temperature it's hot enough to coke (char) the oil but the constant flow of oil prevents this from happening. If you turn the engine off while the turbo is hot, the oil in the bearing will char and cause terrible wear when it next spools up - it's like pouring fine sand in there. If you let it idle for a few minutes, it will cool below the char point of the stationary oil. Purely synthetic oils are a lot more difficult to char.
posted by polyglot at 9:29 PM on January 11, 2006

What about older cars? The advice I got from the guy I bought my 64 bel air is that "well, you can warm it up by idling, or I just warm it up by driving it". I've taken to letting it idle for about 60-90 seconds in the mornings before I leave for work, sometimes while I squeegee the windows -- should I cut this time down or make it longer?
posted by fishfucker at 10:15 PM on January 11, 2006

When the cold is extreme (-20F) you have to idle for a long time, maybe 20 or so minutes, to get your heating to work enough to keep frost from developing on the inside, from your breath. Otherwise, you've got frost before you drive a couple blocks! At least it was so with my Bronco II (1988). In motion, the thing would develop no heat at all.
posted by Goofyy at 12:57 AM on January 12, 2006

Yeah, in extreme cold such as what goofyy describes, you have to run the engine long enough to get the heater working before you drive it. A block heater can shorten that time. In California, it's just a comfort thing. (Or the up-warmers don't know that it's not required by the car.)
posted by Kirth Gerson at 4:02 AM on January 12, 2006

In terms of driving gently, this means at below 3000 rpm on your tachometer.
posted by OmieWise at 6:27 AM on January 12, 2006

Its RPMs that matter, you can warm it gently by letting it idle in your driveway or by driving at idle (assuming you don't have to turn out on to a busy street).
But if your windows are fogged up, you may need to get the defroster working before you can safely drive, however, you can buy a 12V hair dryer that plugs into the cigarette lighter and is great for defogging.
I've known people with thick oil and tight engines who have blown out their oilfilter gasket by revving too high when cold.
posted by 445supermag at 8:01 AM on January 12, 2006

Older cars with carbs rely on a warm intake manifold to vaporize the fuel before it enters the cylinder. This is also one of the reasons for a choke. When the manifold is cold, it takes more fuel to get a combustible mixture. The same holds true for fuel injected cars, to an extent, which is why the idle tends to jump up a bit higher then gradually come down.

Running oil designed for your climate is a good idea, too.
posted by kableh at 2:14 PM on January 12, 2006