Reports like this of people dying from CO poisoning in idling cars due to "clogged tailpipes" are disturbingly frequent. But how can this happen if the car is outdoors?

First of all, how does a modern engine respond if tailpipes are blocked? If they are obstructed enough that exhaust can't escape the system why doesn't the engine stall?

Second, since the engine does in fact somehow continue to run, how does exhaust end up in the cabin? I'm guessing that there's an obvious weak point at which the backpressure escapes the exhaust system, and that point must be near the cabin air intake? (But if that's the case, would setting the cabin airflow to recirculate prevent the intake of exhaust?)

  • Stock images, false article. Don't believe everything you see on the internet.
    – Mike
    Dec 18, 2018 at 0:13

1 Answer 1


One way I could explain it from that photo, is that there will not have been any snow under the car, so the exhaust fumes will have easily been able to exit from the tail pipe and spread under the car. The fumes will then have gone into the engine compartment and from there could have been sucked in by the fan.

Alternatively the exhaust could have had a hole anywhere along its length which once again would have allowed fumes underneath the car.

If in perfect condition, there should be no where for fumes to exit the exhaust, other than from the tail pipe. If the tail pipe was totally blocked, the engine would slow down and stop. However, there is no way snow would be able to block the tail pipe sufficiently.

Putting the heater on recirculate may have limited the intake of fumes, but a car's passenger compartment is not air tight, so the fumes will still find a way in if the car is totally surrounded by fumes as it will have been in that photo.

  • Thanks: so you agree truly "obstructed tailpipes" should cause the engine to stop. As for where exhaust would go: It's a lot warmer than freezing, and warm air rises, so I'm having trouble imagining an outdoor scenario in which fumes discharged under the car don't rise quickly around the cabin to dissipate above the car.
    – feetwet
    Feb 26, 2016 at 20:45
  • 1
    @feetwet. If you look at the photo, the lower part of car was totally sealed with snow, so there will have not been anywhere for the fumes to go other than underneath.
    – HandyHowie
    Feb 26, 2016 at 20:48
  • Indeed: good observation!
    – feetwet
    Feb 26, 2016 at 21:06
  • @feetwet if you look at the bottom of a car the sides are usually one of the lowest parts. So it would seem pretty easy for gasses that leak out of the exhust system to end up rising under the bonnet and getting sucked into the ventilation system. Feb 26, 2016 at 22:30

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