Smoke Coming From Under Car Not Hood: What It Means: Explained

> **Quick Answer:** Smoke from under the car but not the hood usually points to burning oil or fluid that has dripped onto the exhaust system, an overheating brake caliper, or a catalytic converter issue. It is rarely an engine fire, but it is never something to ignore. Pull over safely, kill the engine, and get everyone out while you figure out what you are dealing with.

## What It Might Mean

The exhaust system runs the full length of your car, from the engine bay back to the tailpipe. Any fluid that drips onto a hot exhaust pipe, catalytic converter, or muffler will burn and produce smoke. That smoke rises and exits from below the car, not from under the hood.

Here are the most common causes, ranked from most to least common:

**Burning fluid on the exhaust.** Oil, transmission fluid, and power steering fluid all drip from above and land on hot exhaust components. The result is white or blue-gray smoke with a sharp, acrid smell. This is the most frequent cause.

**Overheating brake caliper or rotor.** If a caliper seizes, it keeps the brake pad clamped against the rotor. The friction generates intense heat and burning rubber or metallic smoke. You will often feel the car pulling to one side and notice heat coming off one wheel. This is a [brake failure warning](/brake-failure-while-driving-what-to-do-immediately/) you cannot drive through.

**Catalytic converter running hot.** A clogged or partially melted catalytic converter can glow red and burn anything nearby, including road debris, grease, or undercoating. The smell is sulfuric, like rotten eggs.

**Grease or debris on the exhaust.** Sometimes a mechanic applies too much grease to a component, or road debris gets lodged against the exhaust. The smoke will clear after a few minutes once the material burns off. Still worth investigating.

**Transmission fluid leak.** Automatic transmission fluid dripping on a hot exhaust pipe smells sweet and produces thick white smoke. If you have been noticing [transmission slipping](/transmission-slipping-on-highway-emergency-steps/) before the smoke appeared, those two problems are almost certainly related.

## What To Do

1. **Pull over immediately.** Do not wait to find a better spot. Get off the road, ideally onto a flat surface away from traffic.

2. **Turn the engine off.** Remove the ignition key. This stops fuel circulation and reduces fire risk.

3. **Get everyone out of the car.** Move at least 100 feet away, upwind. If you are on a highway shoulder, stay behind the guardrail.

4. **Do not open the hood yet.** If the smoke is from under the car, you probably do not need to, and opening the hood can feed oxygen to a small fire you did not know was there.

5. **Look under the car from a safe distance.** Check whether the smoke is coming from a specific wheel (caliper issue) or from center or rear (exhaust or catalytic converter).

6. **Smell the smoke.** Burning oil smells sharp and acrid. Transmission fluid smells sweet. Brakes smell like burning rubber or hot metal. Catalytic converter smells like sulfur.

7. **Do not drive it.** Even if the smoke seems minor and stops after a minute, you need a mechanic to check it before you put more miles on the car. A seized caliper can lock up completely. A fluid leak can drop to a dangerous level fast.

8. **Call for a tow.** This is not a situation where you limp it home. If you are on a highway, read up on [what to do when your car breaks down on the freeway](/car-broke-down-on-freeway-what-to-do/) before you step out of the vehicle.

![mechanic car repair](/images/smoke-coming-from-under-car-not-hood-what-does-it-mean/mid.jpg)
*Photo: Pexels*

## What It Might Cost to Fix

| Cause | Repair Cost Range |
|---|---|
| Fluid leak (oil or transmission) | $150 to $800 depending on source |
| Seized brake caliper | $250 to $600 per corner |
| Catalytic converter replacement | $900 to $2,500 |
| Exhaust pipe repair or patch | $100 to $400 |

Towing to the shop typically runs $75 to $175 for local hauls, more if you are in a metro area. See [car radiator leak and steam situations](/car-radiator-leak-steam-coming-out-tow-cost/) for a comparison of how tow costs break down for similar emergencies.


![tow truck road](/images/smoke-coming-from-under-car-not-hood-what-does-it-mean/bottom.jpg)
*Photo: Pexels*

## Stay Safe

- Never crawl under a smoking car to investigate.
- If you see flames, not just smoke, get 300 feet away and call 911 immediately. A [car fire on the highway](/car-caught-fire-on-highway-what-to-do/) escalates fast.
- Keep a fire extinguisher rated for Class B fires in your trunk.
- Do not restart the engine to move the car a short distance. You may turn a manageable problem into a fire.
- If one wheel well is the smoke source, do not touch that wheel or brake components. Calipers can reach temperatures above 400 degrees Fahrenheit.

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*Need roadside help? Visit [Tow With The Flow](https://towwiththeflow.com/smoke-coming-from-under-car-not-hood-what-does-it-mean/) for real answers when your car breaks down.*