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I have been reading mixed reviews about how long to let your car warm up before driving in the winter months. Most of the articles say that the best way to warm it up is to let it idle for 1-2 minutes, then drive gently until it reaches its optimal temperature.

My concern is the following:

When I start the car in cold weather the tachometer usually sits around 1500 rpm - 1750 rpm. When it has been running for a while it idles at 750 RPM and the car runs much smoother when it's at this point. It takes almost 10 minutes of idle to get it warmed up to 750 rpm (in about -10* weather).

Is it smart to idle and wait for it to get to it's regular RPM before driving off?
Will driving off before it gets to a low RPM be harmful to the car in the long run?

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13 Answers 13

up vote 15 down vote accepted

I would agreee with the articles - waiting a minute or so (generally the time it takes to clear the ice off the windows...) is generally fine.

As the other answers say, the engine will idle high to start with, as the ECU compensates for the colder block and thicker oil by running the engine richer. This will cause more wear to the engine, as the oil is thicker and so won't lubricate as well as normal, but it will do so whether you are stationary or moving, so you might as well be moving. The key thing is to make sure the engine gets a chance to warm up properly over the course of the journey - lots of short journeys in cold weather will be bad for the engine as the wear will be proportionally higher.

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I'd also add (the obvious) that one should keep their acceleration and engine speed tame while the engine is warming up. The less load the better, but as you said, there's no sense in just idling. – Shamtam Feb 17 '15 at 5:34

One other thing to keep in mind when letting a car warm up. You're only warming up the engine. Remember all the other components that stay cold until driven: rear end, shocks, suspension components, tires, etc. So even if you let a car warm up until the engine is closer to operating temperature, you should still drive easy at first, until all components have been brought up to operating temperature.

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The engine coolant temperature sensor in your cars engine, together with its inlet air sensor work together to decide the operating of your cars engine at start up. When its cold the fuel injectors are commanded to inject extra fuel, and your cars idle speed control valve is commanded to increase idle speed to prevent the engine stalling from a now richer mixture. As the engine warms up, the engine management system trims it back to the lower idle speed you describe. This is what it is supposed to do. As long as the temperature does not drop to the point where it freezes the engines oil, driving the vehicle considerately will not harm the engine. The advances in the technology of metals used today afford them properties way in excess of what they were a couple of decades ago. Simply put the engine runs better when its at its operating temperature, take it easy till then. In extreme cold conditions an engine block heater set up may be a good idea. My son took a snow sports holiday in Canada from the UK, and he told me it could get very very cold, overnight especially.

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The basic idea is to not beat on the car too hard until the engine has had a chance to get somewhere near normal operating temperature. Driving gently at first will warm it up fine (and save gas) versus just sitting idle. If you're scraping snow off, I'd go ahead and run it while I'm doing that, since I can take advantage of the electric defroster to aid the cleaning of the vehicle.

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Yes. You should allow your engine to warm up a bit.

If the temperature is exceedingly cold, say -10c, you would want to allow an extra minute or two to heat up and even out the temperature between components a bit.

If you were to start you car in extremely inclement conditions and raced it full throttle up a hill with high load there would be a potential for differing expansion rates of material. The head gasket between the crankcase and the cylinder head could show weakness as the differing expansion expands one component a bit more than the other and over time weaken adhesion between the two surfaces resulting in a failure.

Another component of extreme cold is the thickening of oil. As @Nick.c stated. Thick oil can become an issue, it's difficult to pump and the majority of it's lubrication properties can be effected in extreme cold. Allowing the oil to heat and the various components to heat up is a good idea.

Additionally, since we are here, I would like to dispel some myth's about engine heating in the morning. There is quite a bit of attribution that IMO is myth.

Would like to clarify a few points of interest

There are several myths regarding why older engines are required to warm up slowly.

Myth 1

Carbureted engines needed to warm-up longer because of the carburetor.

Running a carburetor on choke doesn't ruin your engine. It will run rich. It can foul your spark plugs if it doesn't come off choke, it can build up a little extra carbon in your combustion chamber over the years but it will not damage your engine. In fact, there are a lot of benefits to your engine when it runs richer. The exhaust is cooler and it's easier on your exhaust valves and it lubricates the valve face impacting the valve seat

Myth 2

Allowing your car to warm up is a waste of fuel

That's what is called a Straw Man argument. The question was "How long should I let me car warm up in the winter?" The waste of fuel response is a legitimate environmental concern. That is not what this is about.

Myth 3

You don't have to warm up new engines they're made out of aluminum that was a procedure for old cast iron blocks.

Cast iron blocks don't crack when run from cold. False claim. Where are the citations on this?

Myth 4

When the engine first starts in cold weather, the oil is warming. The rings on the pistons are reseating, from being cold

The rings are reseating is not something that happens. They are already seated and worn in from use. Running the engine at idle and allowing it to warm will not reseat the rings.

Myth 5

your engine needs a chance to get the oil circulated through it

The engine has oil circulating in it almost immediately. This does not take but a moment. False claim.

Myth 6

The aluminum piston will expand quicker than the the steel cylinder liner and you would seize the engine.

Pistons are now made of hypereutectic alloy. Hypereutectic alloy has a lower expansion coefficient of expansion which allows for tighter tolerances than previous materials. There is point in mixing allows called the eutectic point where the mix of alloys becomes one and their lattice structures intertwine and they become 'one'. Of course this is overly simplistic explanation for the sake of this answer.

In short, piston expansion is no longer an issue with modern vehicles.

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Well, most cars (generally economy/general commuter) have hypereutectic pistons. Some performance cars do come with forged pistons that do have expansion issues. However, seizing them is not an issue. The issue is that they need to get temperature so that they expand for proper fit/function. – Brian Knoblauch Feb 3 at 1:42

I think you're over thinking this. When it comes to basic operation, Your owners manual will tell you everything you should do and more. I would suggest going by whatever it says...If it doesn't say anything about cold weather starting, then nothing to worry about. I've read more opinions over the years suggesting that idling more than a couple of minutes is actually bad for your engine than I've read that it's good. Sure, it's a good idea to give it a few minutes before driving off when it's really cold, but it's more of a guideline than a rule. I find its good to keep the engine below 3000 rpm till its warmed up. Bottom line is, it's a well made modern car...use common sense, and you'll be just fine.

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Your car idles high in the cold because of poor air/fuel ratio. The car makes certain adjustments, causing the RPM to be a little higher. Letting it sit until the RPM goes down will not hurt the car and is the best practice for letting it warm up.

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AFR will be perfectly fine on a modern fuel injected car. However, for a carb'd car with a choke, you're correct. You are forced to run overly rich until the carbs warm up and can function properly. – Brian Knoblauch Feb 16 '15 at 12:55

First you should fint out if your car has proper idle RPM on cold engine. For example my car and most of the cars (as far as I know) keeps steady 750-800 RPM no matter how cold the engine is. Maybe your car (ECU) was designed that way or maybe something is broken (sensor or idle valve etc.). From my observations car warm up much faster while driving gently rather then staying on idle. So i think for the engine it's better to drive off immediatelly (of course very gently until it warms up).

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That sounds like your car might have an issue. Anything OBD-I or newer should idle high when cold. It's part of the emissions package. Until operating temperature is achieved, the emissions are high, so they idle fast to warm up and get those emissions down. – Brian Knoblauch Feb 3 at 1:45

Yes you should always let your car warm up until it is atleast throwing heat ... your engine needs a chance to get the oil circulated through it.... and your transmission is also warming at the same time... many people that dont warm up there cars they complain about having issues with it....

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In Great Britain, vehicle owners are only allowed to warm their engines for no more than one (1) minute prior to leaving due to their strict smog laws. Sometimes, as has been stated, allowing a vehicle to warm is not an option. Also, most newer cars utilize thinner oil (0W-20 v 5W-30) which flows much easier in the cold, so is not as much of an issue these days. – ᴘᴀᴜʟsᴛᴇʀ2 Nov 26 '14 at 19:31
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Paulster2 - I don't think that law still exists. It may be a local council regulation in London still, but smog has not been an issue since the late 1800's here :-) – Rory Alsop Feb 16 '15 at 11:44

When the engine first starts in cold weather, the oil is warming. The rings on the pistons are reseating, from being cold, therefore contracted! As the engine runs, and warms the rings, they expand, as do the valves, even the Pistons, as do most moving parts. If the car has a standard transmission. One should shift it into neutral in order to warm the drivetrain. Making sure the car is warm enough too do so,without stalling the engine. With the newer aluminum engines there should be even more contraction, & expansion. Internal combustion engines do warm guickly. I idle mine in the cold for approximately a minute or two, and then I shut it down. I than restart it, when I'm ready to go. Usually the car begins to blow heat fairly soon after this procedure. A car is a major investment. Very ($) expensive to repair. I agree about taking it slow, & keeping the rpm's down until all systems have warmed.

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The RPMs are higher in the cold because engines are pretty inefficient at cold temperatures. That, and the increased viscosity of cold oil mean the engine has to use more energy to run. It does this by increasing the amount of fuel used and increasing the air intake, which makes it idle higher. It's normal.

The main idea is to allow the oil to circulate and build pressure (5 seconds or so after starting), and bring the oil and engine up to a reasonable temperature (a minute or two).

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You don't have to warm up new engines they're made out of aluminum that was a procedure for old cast iron blocks, they weren't very tolerant to sudden temperature changes and were liable to develop cracks.

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How do you account for the tighter tolerances then? It is still best to at least let your car run for a minute prior to going somewhere as you will see increased wear. Even aluminum blocks have cast iron cylinder liners. If you have references which prove your point, it would make for a much better answer. – ᴘᴀᴜʟsᴛᴇʀ2 Oct 31 '15 at 1:42

I assume letting your car idle will depend on how long its being parked. Eg, let's assume I parked my car for about 2 hours. I will not let my car idle for more then 5 minutes, of because if I had it parked for 12 hours irrespective of what the weather is. It should idle about 10 to 15 minutes. You will come to terms with the actual time according to the heat gauge once it is in operating temperature you set to go. It's like when you wake up in the morning you can't eat without refreshing up take that as an Eg. I'm not saying your car won't run if you just start and move but it will wear down your engine. Remember oil needs to circulate freely. The car's idle will be high you'll step on the pedal! You'll be wasting gas at times it gives a jerky ride until in normal rpm.

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