Steam coming from under the hood

Symptoms

• Visible steam or vapor rising from under the hood
• Sweet smell often accompanying the steam
• Temperature gauge reading high or in the red
• Possible coolant loss on the ground beneath the vehicle

Likely causes

• CommonCoolant leak dripping onto a hot engine surfaceCoolant contacting the hot engine block, exhaust manifold, or other hot parts vaporizes and produces visible steam.
• CommonSystem overheating and coolant boilingOnce coolant temperature exceeds its boiling point, it can boil and produce steam, especially if it escapes past the cap.
• Less commonAC condensation mistaken for steam (usually much less dramatic and only near the front bumper)Normal AC condensation is a small amount of clear water, not the more dramatic vapor associated with hot coolant contacting engine parts.

What to do

1. Pull over to a safe location as soon as you notice steam; do not continue driving.
2. Turn off the engine and do not open the hood immediately; let it sit for a few minutes to let steam and heat dissipate somewhat.
3. Stay clear of the front of the vehicle and any steam plume, since it can be very hot.
4. Once it's safer, carefully open the hood from a distance if possible, keeping your face and body away from the opening.
5. Do not touch the radiator cap, hoses, or any engine components until everything has cooled substantially, generally 20–30 minutes or more.
6. Once cool, check the coolant level and look for the source of the leak causing the steam.
7. Have the vehicle towed rather than driven further if the cause isn't a simple, safely correctable low coolant level.

Tools and parts

• Gloves

When to call a pro

See a mechanic once cooled and towed or driven cautiously a short distance, especially if the cause isn't an obvious and simple coolant top-off.

Safety