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I have a Nissan Xtrail, 2.0 Diesel with DPF. My routine is like this:

  • During the week, 3 or 4 days I drop my kid to the kindergarten, then leave the car at home and take the bus.
  • Thursday and/or Friday I take the car to work, also in the weekends I use the car

I dont really drive the car in stop and go traffic.

So, when I take the kid to kindergarten, I drive a mile, leave the car running for 5 minutes, while I leave the kid there, drive the car back home for another mile.

Should I stop the car during that 5 minutes stay at the kindergarten? I leave it running, just to get the oil / coolant temp high.

Thanks.

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    When do you do a drive of 30 or 40 miles to get the engine & dpf properly hot? if you don't you will pay... – Solar Mike Sep 3 at 11:58
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    Leaving the car running unattended near a kindergarten: Sorry, there are a lot of things wrong here.. – Martin Sep 3 at 13:06
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    I’m nearly positive that if you leave engine running, even with the door locked, will result in NO insurance coverage for vehicle theft. Best to check with your insurance company. – zipzit Sep 4 at 2:28
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    Wow, many states (USA) have laws about not leaving keys in unattended vehicles. Check out this link – zipzit Sep 4 at 2:35
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    @zipzit It's illegal to leave a car running unattended in the UK too. – Nick C♦ Sep 4 at 9:03
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Should I stop the car during that 5 minutes stay at the kindergarten? I leave it running, just to get the oil / coolant temp high.

Idling isn't a great way to warm the engine up - since there's no real load on the engine you aren't going to generating much heat. I think in your use case it's better for it then stopping the car and cutting it into two small trips since it won't have gotten anywhere near warm in a mile of driving.

That said there are environmental/air quality concerns about unnecessary idling - especially with a diesel. I hate to sound like "that guy"but 25 mins of extra diesel fumes being kicked out a week isn't great, especially near a kindergarten.

You don't mention the length of the other trips that you do but it has to be said if you aren't getting some regular lengthy trips in you're going to kill the DPF very, very quickly.

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    Agreed, especially since fumes of a cold diesel engine are worse. – Martin Sep 3 at 13:04
  • When I take the car to work, I do 24 miles to and back from the office. The cruising speed is constant, about 50-60 mph. In the weekends I travel about 100 miles. No stop and go traffic. The car has 100.000 miles. I've had it for about 4 months, with 5000 miles added by me. No DPF light so far. DPF has not been removed. – eonootz Sep 3 at 14:35
  • @eonootz sounds like you're doing some decent runs in it then - so it shouldn't be clogging the DPF up excessively. – motosubatsu Sep 3 at 15:53
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The real issue is that short trips will not allow a full DPF cycle, and your car will continue to attempt to run a cycle until it is able to complete a cycle. This may result in poorer fuel economy.

Idling will usually not help, as the exhaust heat output has to be higher to clean the DPF.

If once a week you do some highway driving for 50 miles it will help periodically clear the DPF, but I am not saying to go for a drive just to do that. But I will say that you will likely at some point have a DPF issue if you can not do longer, higher temperature runs like that. And you will use less DEF if you always do trips like that.

You might want to read up on the DPF cycle, so that you better understand how this sub-system on your car works.

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  • Which would go out faster, the starter and alternator, if i stop the car. Or the DPF if I keep it running for 5 min everyday? – eonootz Sep 4 at 9:08
  • The DPF would be a greater risk. But if just for 5 min every day, it may take months before you had a problem. And soot buildup gets erased when you do a longer trip which gives a scavenging opportunity. So take a day trip with your children every now and then... – mongo Sep 4 at 13:42
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    FWIW, I agree with shutting down the engine when doing the school drop off. The risks of leaving an engine running, and having kids get in and out of the car with the engine running are greater IMO than the risk to the car. After all, how many cars is a child worth? Accidents happen. – mongo Sep 4 at 13:45
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    @eonootz - while I agree the DPF is likely to be the problem sooner (by a long way, especially given only a tiny bit of extra wear on the starter and pretty much none on the alternator), the starter and alternator on most cars are likely to be a lot cheaper and easier to replace than a DPF. – Kickstart Sep 5 at 8:08
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As an longtime owner of a DPF diesel I have the following thoughts about your question:

Both DPF and engine don't like cold idling (wear on the engine due to cold oil, acidic combustion byproducts and clogging, especially since a cold diesel engine produces lots of soot and your engine oil starts cleaning only when warm). Since a diesel has a rather efficient combustion it won't warm up soon, so a mile isn't enough to get your engine up to operating temperature. In the makes I know the DPF will only start its cleaning cycle under some very defined parameters (the engine is up to temperature and is running above a certain speed for a certain time). A two mile trip and 5 minutes idling won't allow a filter regeneration.

The wear on the alternator by an additional start per day should be negligible, especially if you compare it with the cost of an clogged DPF/EGR or possible engine damage.

As long as you have prolonged trips under high load on most of your driving time you should not worry about the DPF. Yes, the DPF would prefer it to be hot the entire time, but 3-4 short trips per week with your driving profile (your comment to motosubatsu) won't do damage.

Bottom line:

The 5 minute idling is contraproductive, both for your engine and surroundings. It fills your engine and exhaust treatment with soot and acid from the bad combustion, won't contribute to filter regeneration and increases wear on your engine.

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