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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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10 Answers 10

up vote 10 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 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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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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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. –  Paulster2 Nov 26 '14 at 19:31
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 at 11:44

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 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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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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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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