Warm Your Car Up Faster

February 24, 2010 at 1:09 am 32 comments

My friend Todd told me about this secret many years ago. He has rebuilt more cars in his suburban home garage than anyone I know.

I met Todd at my first part time job, we used to work early weekend mornings during high school. I was too young to have a driver’s license, so my dedicated parents would always drive me.

That was before remote starters, so I would usually start the car a few minutes before leaving. Actually, that’s not true — my Dad was usually the one starting the car a few minutes before I was ready to leave, which was about 10 minutes after I told him I would be ready to leave.

It didn’t make much difference to the car — it was still cold for at least half the trip. On the rare occasion that I started the car, I would turn the heater to its hottest setting and turn the fan to full blast. That’s actually the slowest way to warm the car, so lets talk more about the fastest way.

The trick is very counter-intuitive, so I want to briefly explain how the car heater works for this secret to make sense.

The item pictured above is a heater core. Most cars have one of these inside the dashboard. Hot liquid passes through the fins, which are there to create a lot of surface area so that air passing through can pickup as much heat as possible before it comes out the air vents. It works just like the radiators in many older homes in that sense.

The liquid is heated by excess engine heat, so if the engine is cold then you won’t get any hot air from your air vents. Your engine has a cooling system which is designed to draw heat away from the engine so it does not overheat. The heater works in a similar way, removing heat from the engine and using it to heat the air being blown into the passenger compartment. So, when you turn on your heater, you are essentially cooling the engine by transferring some of its heat to the inside of the car.

To heat the engine faster, you want to stop that heat loss. It’s similar to heating your oven, you don’t leave the door open because you’ll lose all of the heat.

You want to turn the heater off by moving the temperature control all the way to cold. Also, turn the fan off to ensure it is not blowing air across the heater core which transfers heat away from it. This will trap the heat in the engine cooling system (reducing its ability to cool the engine) and therefore heat the engine more quickly. It traps the heat in, just like closing the oven door.

If your car has an automatic climate control system that allows you to dial in the temperature then there is no need to worry about these suggestions to make them heat the car faster, most of these cars do it automatically. If your car has automatic climate control, it’s normal that the fan doesn’t blow when you first start the cold car. The vehicle engineers already know this secret and have programmed it into the car. The fan does not run until there is adequate engine heat to warm the air (unless you want to warm the car more slowly and manually activate the fan).

This knowledge is helpful to all drivers, even if you never plan to drive in cold weather. If your engine is overheating in hot weather, set the climate control to hot, turn the fan on full blast and roll down all the windows. This will dissipate engine heat through the heater core and help cool the engine.

Broken Secrets

Written By: Chad Upton

Available on Kindle

Thanks to Todd M for sharing this secret many years ago.

Sources: 2CarPros, How Stuff Works

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Entry filed under: Automotive, Be Efficient, Demystified, Despite Popular Belief, Hacks, ProTips. Tags: , , , , , , , , , , .

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32 Comments Add your own

  • 1. luis  |  February 24, 2010 at 2:07 am

    you seriously need to make these posts shorter or make your writing more interesting, it’s the internet, no one has time for boring 1000 word posts

    • 2. Chad Upton  |  February 24, 2010 at 2:28 am


      Thanks for the feedback on length. I have cut out about 100 words, just for you. It’s now 629 words and most people should be able to read that in ~2.5 minutes.

      I’m sorry that you find my writing boring. Perhaps you can offer some constructive criticism on why it is boring or what would make it more interesting.

      • 3. chris dawes  |  March 3, 2015 at 12:52 pm

        To Luis’ point, if you could put the actual thing to do to right up front and then explain why then the people with, short attention spans and/or comprehension issues, can know what to do without actually knowing why they should do it. I actually like the explanations, but see too many articles that are very long winded (not this one) and seem to never get to the point.

    • 4. Get a life, Luis  |  December 30, 2012 at 2:27 am

      Luis, go back to living your life in Twitter or SMS-sized chunks and stop annoying the help.

  • 5. luis  |  February 24, 2010 at 2:51 am

    I don’t unfortunately, I haven’t taken English classes at a collegiate level yet. I don’t mean to be a jerk, by the way. I just feel like the basic premise behind your blog is great but I constantly find myself losing interests in your posts cause of their length and inability to get to the point. I mean its always good to back up your information with facts that help you further comprehend the idea but it’s probably not all that necessary on the internet. Try the 1000 Awesome Things blog for instance, short and sweet posts for the most part. Anyway, sorry if I came off as condescending. Just having a bad day I guess.

    • 6. Bearfoot  |  July 20, 2010 at 11:04 am

      Why is it when people say “I don’t mean to be a jerk” they usually turn around and be a jerk?

      I’m just wondering.

      Seriously dude, I find these articles informative and interesting and not too long at all.

    • 7. Bean  |  December 16, 2010 at 10:26 am

      Hmmmm, speaking of being long winded, Luis…..

      Anyway, just wanted to point out that f your vehicle is overheating due to a loss of fluid, water will not likely be passing through the heater core. This is also true if you have a block in the smaller lines servicing the heater core due to frozen coolant or a steam block.

  • 8. L.Bo Marie  |  February 25, 2010 at 9:28 am

    I appreciate that the articles are a little longer- I’m constantly annoyed at the fact that things are dumbed down or shortened to make things “faster”.

  • 9. Angela  |  February 25, 2010 at 2:47 pm

    Honestly, I can’t believe that anyone would have a problem reading these so-called ‘long’ posts. These posts are NOT long. They are literally about a page of text, which is not a lot to read at all. Have we really become that needy that we can’t read a page of text before getting to the point of it?
    I recently stumbled across this site and I absolutely love it and find it very interesting! I have no problem with reading the longer posts, it only takes a couple minutes of my time and I would much, much rather have something be a little bit longer and explained in detail rather than have the secret be explained in a short paragraph.
    Thanks Chad, you are awesome!

  • 10. Janec72  |  April 13, 2010 at 11:49 pm

    First of all, nobody’s holding a gun to my head to make me read a long internet article. My time is valuable. If it’s a subject that interests me, and the article is not overly rambling, I’ll keep reading.

    Secondly, while it is true that the heater core of any car engine can act as an auxilliary radiator (ie: by cranking the car’s interior heat you can reduce the engine’s temperature), the author may have overlooked a useful damage-saving measure.

    Your car’s engine will indeed heat up faster with the car’s interior heat selected OFF. However, the potential for damage happens with the *next* step…

    You get in your pre-heated car with the cool-interior-but-warm-engine, and immediately select the equivalent of “toasty interior” not to mention “defrost my frosty windshield” — All that very warm air suddenly blasts onto a very cold windshield.

    Have you ever noticed how many windshields are cracked clear across the bottom, but not across the top or even the middle? — Yep, that’s from hot Defrost air hitting ice-cold glass.

    *Instead*: Select Defrost (only) when you start your car. The windsheild will warm slowly enough to prevent cracking, the engine will warm up fairly efficiently, and you can crank up the interior heat after you’re on your way.

  • 11. Boogs  |  April 20, 2010 at 2:24 pm

    Format your posts in a way that the short and easy is the first part of the post, and the Why Does It Do This is at the bottom. I’ll still read it all. : )

  • 12. Wayne  |  June 4, 2010 at 8:37 am

    I’m not sure on this, if you can tell me where I am wrong I would appreciate it:

    The car interior is heated by using a heat exchanger, that is flowing interior air over cooling system lines. To the best of my knowledge there is a thermostat in the cooling system that prevents the coolant from circulating until a certain temperature is reached. By the time that temperature has been reached and the coolant is being used to heat the interior air, the engine should be sufficiently warmed up.

    I agree with your post in principle, I think in practice it will not matter if you run the heat or not.

    Thanks for your time, and correction to my understanding.

  • 13. janec72  |  June 4, 2010 at 9:27 pm

    @wayne: you are correct that the thermostat prevents the engine coolant from circulating until the temps are up. However, the interior [electric] defrost fan will run, if so selected, from the beginning.

    If you run the defrost fan from the beginning, it will circulate air that is gradually warming… On the other hand, if you flip on the defrost at the last minute, after the car is well preheated, HOT air will suddenly be flung at the cold windshield, thus causing (or exacerbating) cracks.

    My conclusion: Preheat car with interior heat OFF, but windshield defrost ON.

    • 14. vw  |  January 28, 2013 at 10:58 am

      yeh thats not important very low chance of that happening

  • 15. Janelle  |  November 16, 2010 at 2:18 pm

    Ahh the ADHD generation….I am really enjoying your writing keep it up!

  • 16. Stephen Woolhiser  |  December 13, 2010 at 10:16 am

    Wow I can’t believe this works. Thanks!

  • 17. Sarah  |  February 2, 2012 at 2:08 am

    I’m going to try that this morning and see if m warm when I’m halfway to work

  • 18. Rogers  |  December 23, 2012 at 11:09 pm

    Great article. More like common sense that is not common at all…
    I was doing just the reverse…..
    This article make much sense..
    Usually when temperatures are below nregative 30 degree celsus(-30C), I blockheat my engine over night. It is this a good practice. Does it make any different if I block heat only for 2H or so……

  • 19. Jane  |  February 7, 2013 at 9:45 am

    Yay! Thanks, Mister!

  • 20. ⭐ Dastardly Pants (@Dastardly_Pants)  |  November 19, 2013 at 3:49 pm

    This post is cool, or should I say hot. Perfectly concise and informative. Brilliant.

  • 21. Garry  |  January 8, 2014 at 2:43 pm

    Actually, this is not entirely correct. The engine thermostat prevents flow through the radiator until the engine warms, but it does NOT prevent flow through the heater core. Thus, the quickest way to warm the interior is to turn the heater on immediately.

    Leaving the heater off will warm the engine slightly faster, but I’m assuming we’re going for personal warmth when we “warm up the car”.

    • 22. -jodi  |  January 21, 2014 at 5:09 pm

      Actually, my interest is not in personal warmth these days. This winter, my car developed an issue with not being able to defog/defrost the side windows and I’ve noticed that it’s when it’s below 32F outside. My car isn’t reaching optimal temp until about 30 minutes of running (granted, we keep getting well below freezing this winter and that’s not normal for here)! By that time, though my windshield is fine, my side windows have fogged and frozen! I had the car checked – heater core is fine and no radiator leaks. The car is a 2006 and I’ve not had this issue until this winter. It’s always been an outside car and I’ve always had to blast the defrost and turn on the rear defrost from the get-go. Thoughts/suggestions are much appreciated.

      • 23. chris dawes  |  March 3, 2015 at 1:02 pm

        You need to make sure that fresh air is coming in. There is a switch that either recirculates air, used for A/C or keeping bad air out of the car, or that lets fresh air in from outside the car. If the switch is on re-circulation, the water vapor from you and passengers can actually freeze on the interior of the windows. If the fresh air is coming in then this water vapor is forced out of the car.

      • 24. -jodi  |  March 3, 2015 at 4:51 pm

        TY Chris and I totally agree about the fresh air bit. Unfortunately, it’s not the setting. I RARELY use recirc. What I’ve found though, is that IF my windows aren’t frozen shut (something that happens WAY too easily on this car), and I just even barely crack a front window and the opposite side rear window, to get some better circulation, that I’ve not had the issue. TY very much though!!! : )

  • 25. Carmen  |  January 26, 2014 at 10:57 am

    Ha-ha! This is exactly what my husband explained but I didn’t believe him! I’ve apogized.

  • 26. Gregan  |  January 5, 2015 at 11:10 pm

    I think this is total bollocks. The oven door analogy doesn’t prove your point at all, in fact I think it points otherwise.

    If your goal is to heat your kitchen, whether you leave the door open the entire time or closed for a portion of the heat up time the amount of heat transferred to the kitchen over time would be identical assuming the heating elements in the oven never turned off.

    • 27. chris dawes  |  March 3, 2015 at 1:04 pm

      The goal was to warm the oven, not the room!

  • 28. Cold Car  |  February 2, 2015 at 1:48 pm

    There are people out there stupid enough to think setting the heater to hot, which stays cold until the car is hot, will WARM THE CAR UP QUICKER?

    Jesus christ

  • 29. justin  |  November 30, 2015 at 10:39 am

    I know this is an old thread but I thought I’d just add some useful information to help out.. yes by turning the heater full blast when idling the car to warm it up will not directly heat the car faster because your pushing cold air through the heater core cooling the coolant back down slightly. But here’s the thing, to drive a car as most people know from start-and-go in cold is very bad for a motor, so take into account you want to be warm, but you want the oil and metal inside the motor warmed up aswell, when you look at a type of oil (example 5W30) the 5 is the viscosity of the oil in the summer and the 30 is the viscosity of the oil in the winter, so for 1 it’s often advised to run 5w20 or 10w20 instead of the 30s in the winter to have thinner oil for easier cold starts in the winter, now back to the point, If your starting your car in the winter, turn your heater ON turn your front and rear defrost ON and most important turn the air recirculation ON this way instead of pulling cold air from the outside it forces air from the cabin back through the heater core, resulting in not just dumping cold air over your warm coolant, but whatever warm air is inside will be heated up again this will gradually heat the car to not cause cracks in window glass, as well as warm you up, at the same time warming the motor aswell instead of driving off of a cold start.. also just to finish it off most cars designed for cold climates will come with a sensor that will run the motor at a slightly higher rpm when it’s below a certain temperature, for example my 2004 RSX type s runs at 2000 rpm for the first minute or so to warm everything up safely and effectively before leveling out at it’s usual 700rpm. This goes to show you the car manufactures have thought these things through, winter isn’t anything new and they design cars keeping in mind some people are completely clueless on the subject. So I say crank your heat as usual just turn on air recirculation and your car will be warm enough to drive mechanically as well as comfortably sit in within 5-10 minutes….. oh and don’t forget to turn off recirculation when you get back in the car as it will cause your windows to fog up…

    My sources: I’m a certified mechanic..

    • 30. Chris  |  November 30, 2015 at 11:20 am

      I am glad you mentioned to turn the recirc off as if people do not the windows will fog up and if it is really cold and your heater is not working well the water vapor from the people in the car could freeze on the interior of the windows. I have seen this in Michigan and wished I could have helped those people with this problem.

    • 31. Steve  |  January 23, 2016 at 2:07 am

      Dear Justin,

      If a certified mechanic knows that the first number in oil description is for summer viscosity and the second is for winter viscosity I can only feel very sorry for all cars you’ve ever worked on !!! This is totally wrong (actually first figure regards winter and second regards summer viscosity) and may have extremely negative effects on those who listen to your advice ! The use of inappropriate oil in extreme conditions (both cold and hot) will lead to engine wear in very short time. But you don’t have to believe me, believe SAE (http://www.viscopedia.com/viscosity-tables/substances/sae-viscosity-grades/) or find as many oil temperature charts you want.

  • 32. Dave  |  March 8, 2016 at 8:45 am

    If you run the heater only in defrost mode with temp set on hot a car with functioning air conditioner reverses the air conditioner under these conditions and actually turns AC into a heater. It starts defrosting almost immediately. An added benefit is that it lubricates your air systems works and extends the life of the seals for your air conditioning.


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