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White Smoke from Exhaust

Clouds billowing out the tailpipe? That’s not morning steam. That’s coolant or fuel sneaking where it shouldn’t — and it can kill an engine fast.

Why It Happens

Engines are only supposed to burn fuel and air. White smoke means something else is tagging along. On cold mornings, a bit of steam is normal. But thick, lingering white clouds usually mean coolant is leaking into the cylinders (blown head gasket, cracked block, or bad intake gasket). Sometimes it’s raw fuel on diesels, but coolant is the wallet-killer.

Most Common Culprits

  • Blown head gasket – classic coolant leak into cylinders.
  • Cracked cylinder head/block – rare but catastrophic.
  • Intake manifold gasket leak – coolant sneaks in.
  • Bad injector (diesel) – dumps raw fuel, makes white haze.
  • Condensation (normal) – light vapor, disappears in minutes.

What You Can Check

  • Watch the exhaust — quick mist on a cold start that clears = fine. Thick white clouds that hang = trouble.
  • Smell it — sweet = coolant, acrid = raw diesel fuel.
  • Check coolant level — dropping with no puddle means it’s going out the pipe.
  • Pull dipstick — milky oil = coolant mixing inside the engine.

What a Mechanic Will Do

  • Pressure test the cooling system.
  • Check compression/leak-down in cylinders.
  • Look for coolant contamination in oil.
  • Test injectors on diesels.

Rough Damage to Your Wallet

  • Intake manifold gasket: $400–$800.
  • Head gasket: $1,500–$3,000+.
  • Cylinder head/block replacement: $2,500–$5,000+.
  • Diesel injector replacement: $300–$600 each.

When to Park It

Light steam on cold mornings? Drive on. Billowing white clouds that smell sweet? Park it. Every mile you drive with coolant in the cylinders is one step closer to a cooked engine.