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My father bought a new car and in the owners manual it advises to keep the engine running for a little while after stopping, the car in question is a 2016 Skoda Rapid with no turbo on it.

I know in turbo charged cars, you should keep the engine running after spirited driving for a few minutes so that cool oil can reach the turbo charger but what about normally aspirated cars, should I do the same so that cool oil circulates the engine block. And if so, is it also a good idea to do the same even if you were not pushing the engine hard?

  • I have seen bus drivers do that when they are driving uphill. I couldn't understand the reason, why would you want the engine oil to circulate and cool the engine when the same could be done by switching it off – shabby Oct 5 '16 at 5:51
  • is the engine a TSI (Petrol), MPI (Petrol) or TDI (Diesel)? I believe all the TSI, TFSI and TDIs have a turbo attached to them. The TSI's are not actively marketed as "Turbo" (sports) engines. They are there to increase efficiency rather than output. – Mauro Oct 5 '16 at 9:01
  • It is MPI, we rarely get turbo charged vehicles in Egypt aside from diesel trucks :( – method Oct 5 '16 at 9:04
  • @shabby Simply switching an engine off does not ensure that all of the engine cools uniformly. There are a number of components made of differing metals within the engine and these all cool at different rates. Allowing the engine to idle lets the engine "warm down" thus controlling the rate at which temperature change happens within the engine. – Steve Matthews Oct 5 '16 at 9:31
  • Also keep in mind that when you shut off the engine most of it gets hotter then when it was running. That is because the cylinders are no longer getting actively cooled and that high heat present when shut off then spreads through the rest of the engine, this is called heat washing. – Ukko Oct 5 '16 at 14:13
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Pushing the engine hard, particularly with a turbocharged car, causes heat build-up, as you might expect. However, this heat build-up is not even across the engine - for example, the area around the combustion chambers will heat up more. By running the engine at low load or idle, the circulation of the oil and coolant helps to even out this heat distribution, avoiding 'hot-spots' - then when you switch it off, the engine cools more evenly, reducing the risk of things warping.

IMHO it depends on the journey you are doing though - if you've just pulled straight off a long motorway run, it's worth letting it run for a minute or so, but if the last few minutes of your journey were pottering slowly through a busy residential area, it's probably not needed, as the engine has been under little load for a while, and so will have cooled somewhat already.

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    Are there any documented cases of premature engine failure due to uneven cooling, though? I think that's the real meat of the question. There's no arguing that things may cool unevenly, the real question is does it matter in practice. Aluminum for example is a great heat conductor and evens itself out quickly. If that isn't addressed then "should I keep the engine running" is still unanswered. – Jason C Oct 5 '16 at 13:47
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    "the area around the combustion chambers will heat up more" Actually, it will stay about the same temperature as the coolant surrounding your engine sleeves. Same thermodynamics principle to putting a paper cup full of water over an open flame- it will never burn. – justinm410 Oct 5 '16 at 18:14
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There is so much speculation in this post. On a modern car, if you seriously think that the manufacturer expects you to leave the car idling after every drive to avoid warping the engine, then I have a bridge to sell you.

Heat is going to conduct to contacting metal many orders of magnitude faster than it will conduct to air. The temperature of the whole engine will reach equilibrium far faster than any one part of the engine will cool down.

Besides, what makes you think your engine heats evenly at idle (when oil flow is the slowest)? Heavy speculation everywhere.

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    If the manufacturers have included it in the handbook then it's manufacturers advice. – Steve Matthews Oct 5 '16 at 12:33
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    Or, probably, the manufacturer's lawyers' advice. You know, those guys who feel that manufaturers have to tell you not to put your poodle in the microwave to dry it after washing it – Mawg says reinstate Monica Oct 5 '16 at 13:05
  • I don't think this answers the question at all. This should probably be a comment. – JoErNanO Oct 5 '16 at 15:33
  • Edited to spell out the absurdity clearly. – justinm410 Oct 5 '16 at 16:48
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I believe most modern Volkswagen based engines since as far back as the 1992 VR6 engine have a secondary water pump which circulates coolant after the engine is shut off. The purpose of this is to prevent damage associated from hot spots which can be created when an engine has been under load.

I am also aware that many people fit an aftermarket "turbo timer" which keeps the engine running at idle for a minute or two after the keys are removed from the ignition or until coolant temperatures drop to a certain level. Again, the purpose of this is to avoid hot spots because different components cool at different rates.

I would say that it is good practice to allow the engine to idle after you've reached your destination. Indeed our 2012 Volkswagen Golf has start-stop technology and there are times when the car will override the start-stop and keep it's engine running when stationary and this is one of a number of reasons it may be doing this.

  • About the start-stop: I once rented a Seat Leon, which seems to be a twin of the Golf. Somewhere in the display menu, it displayed information about why start-stop is not used. Typical reasons were "engine too cold", "Headlights on" or "Slope of street to high". Maybe, you can find out? – sweber Oct 5 '16 at 10:45
  • Mine simply displays the Start-Stop icon with a cross through it. I've not delved into the reason codes but it would be an interesting exercise. – Steve Matthews Oct 5 '16 at 11:04

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