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Why Your Car Smells Like Exhaust Inside (and What to Do)

Smell exhaust fumes inside the car? That’s not “character” — that’s carbon monoxide sneaking in, and it’s dangerous business.

Why It Happens

Exhaust is meant to leave out the back. If it’s finding its way into the cabin, there’s a leak in the system — cracked pipe, bad gasket, or rusted muffler. Sometimes it’s a bad trunk or door seal letting gases get sucked in. Whatever the cause, breathing it in is bad news. Carbon monoxide is odorless and toxic, so if you smell exhaust, you’re already getting more than you should.

Most Common Causes

  • Exhaust leak – cracked manifold, gasket, or rusty pipe.
  • Bad trunk/door seals – fumes pulled into the cabin.
  • Leaking heater core/exchanger in older diesels – exhaust crossover.
  • Idling with rear window open – airflow sucks exhaust back in.
  • DIY exhaust mods gone wrong – loose clamps or bad welds.

What You Can Check

  • Look under the car for black soot or holes along the exhaust.
  • Listen for loud hissing or ticking under load — a leak upstream.
  • Check trunk and door seals for cracks or missing rubber.
  • Avoid idling with windows open at the back of the car.

What a Mechanic Will Check

  • Inspect entire exhaust system for leaks, cracks, or rust.
  • Check manifold gaskets and flex pipes.
  • Test cabin seals and airflow.
  • Use a gas analyzer to detect CO levels inside.

Ballpark Repair Costs

  • Exhaust gasket: $100–$250.
  • Muffler/pipe repair: $150–$400.
  • Full exhaust replacement: $600–$1,200.
  • Door/trunk seal replacement: $100–$300 each.

When to Call It Quits

Exhaust smell in the cabin is not “wait and see.” It’s a health risk. If you smell it, drive with windows down and get it fixed immediately. Carbon monoxide doesn’t give second chances.