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Environment aside is idling a crappy car before driving better than not? All the answers to the like questions always say if you have a new car there is no difference except waste. Is this still true for older cars?

  • I think all you're going to get is anecdotal opinions on this. It's also very subjective. What is considered a "high mileage" car? 20 years ago, high mileage was basically considered anything over 100k miles. Now cars last well past 200k, and 300k is not unheard of ... so, it really depends on what you mean. It also depends on where you live. In England, it's illegal to warm your car longer than 1 minute after startup (at least it was when I stayed there 20 years ago). This wouldn't be an issue they'd consider there. – Pᴀᴜʟsᴛᴇʀ2 Sep 27 '18 at 16:26
  • @Pᴀᴜʟsᴛᴇʀ2 interesting - I've been living and driving in the UK since about 1970, and I never heard about that law (which seems unenforceable in any case). There might have been some local regulations in a particular location, of course. It's certainly illegal to cause excessive noise by running a stationary (or moving) vehicle engine, but there is no particular time limit for that offence. – alephzero Sep 27 '18 at 17:32
  • @alephzero - I may have been told wrong, but when I was getting my international driver's license, that was one of the things which was drilled into us was not to warm up your car for more than a minute. If I got bad poop, I'll definitely change my tune. I just assumed it was to reduce emissions so never questioned it. – Pᴀᴜʟsᴛᴇʀ2 Sep 27 '18 at 17:59
  • @Pᴀᴜʟsᴛᴇʀ2 Hmm... you might be right. Section 123 of the UK Highway Code says "The Driver and the Environment. You MUST NOT leave a parked vehicle unattended with the engine running or leave a vehicle engine running unnecessarily while that vehicle is stationary on a public road. ... However it is permissible to leave the engine running if the vehicle is stationary in traffic or for diagnosing faults." The "MUST NOT" indicates this is covered by legislation, not just a recommendation - but there isn't a statutary time limit and "diagnosing faults" leaves plenty for a good lawyer to work with! – alephzero Sep 27 '18 at 19:20
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    Actually the Highway Code doesn't quite match the law here. The Law says (1) "the driver of a vehicle shall, when the vehicle is stationary, stop the action of any machinery attached to or forming part of the vehicle so far as may be necessary for the prevention of noise. and (2) no person shall leave, or cause or permit to be left, on a road a motor vehicle which is not attended by a person licensed to drive it unless the engine is stopped. (Road vehicles construction and use regulations, 1986). So I think I was right first time, for practical purposes :) – alephzero Sep 27 '18 at 19:32
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Newer or older (subjective as noted in comments) doesn't really matter. Idling a cold engine for a few minutes to allow the oil to warm and flow through the engine is better than running the engine cold under load with insufficient lubrication. When cold, oil collects in the oil pan and is thicker. Once the engine idles for a minute or so, oil is circulated to the top end (camshafts/valves) and rotating assembly, ensuring those parts are lubricated.

If the vehicle is turbocharged, it's recommended to allow the oil to warm to operating temperature before putting it under significant load (approx 90C). "If a cold engine was brought to high speeds immediately after the start, there is a risk that the oil supply in the turbocharger is not yet sufficient and hence the oil film in the turbocharger tears off." Source: http://www.enginebuildermag.com/2015/10/how-oil-change-habits-are-killing-turbos/

I did read in an owners manual for a 2013 car that recommended not warming the engine at idle beyond 5 minutes. It gave no explanation beyond that.

If an engine is warm, there really is no difference between shutting it off and restarting for short stops (such as a stop light) beyond the excess wear on the starter and starting load on the battery. The fuel saved is minimal and of less cost than a starter repair.

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From what I remember from an article which I don't have to hand, idling a cold engine is bad practice, old or new. If your intention is to warm the oil, driving gently away puts a greater load on the engine and therefore generates more heat which brings the oil to operating temperature quicker.

Some vehicles, especially diesels, can take upto 20 minutes to come up to operating temperature at idle and until the oil reaches operating temperature, it isn't providing effective protection. I will try and dig out the article but IIRC it was advice backed by one of the major oil companies. A quick Google search turned up this article from popular mechanics which seems to echo the one I've read.

  • very interesting...... – Muze Sep 28 '18 at 13:43

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