You're driving, the temperature needle climbs, and suddenly a white cloud comes out from under the hood. It's one of the most common scares on the road, and what you do in the next few minutes can be the difference between replacing a hose and repairing the engine.
Here's what to do step by step, the four things you shouldn't do even if they seem logical, and why it usually happens.
Juan tells you in a minute
What to do, step by step
Pull over somewhere safe and turn off the engine
Get out of the lane as soon as you can do it safely. Every minute the overheated engine keeps running can add damage.
Hazard lights and warning triangle
Turn on your hazard lights and, if you can do it safely, place the warning triangle behind the car. Get out on the side away from traffic.
Don't open the hood while there's steam
Steam and hot coolant can cause serious burns to your face and hands. Step away from the front of the car and wait.
Wait for it to cool down
It can take half an hour or more. Only when there's no more steam and the hood is just warm to the touch should you open it to look.
Tell Juan what happened
What you saw on the dashboard, how long you'd been driving, whether there are puddles under the car. Juan tells you what's most likely and what to tell your mechanic.
4 things NOT to do
These are the four most common reactions, and all four can make things worse.
Don't keep driving
An overheated engine can be damaged within minutes, for example with a warped cylinder head. What's a hose today can be a major repair tomorrow.
Don't open the radiator cap while hot
The system is under pressure. If you open the radiator or reservoir cap with the engine hot, boiling coolant can spray out. Wait until the engine is cold.
Don't pour cold water on a hot engine
The sudden temperature change can crack engine parts. If coolant needs topping up, do it with the engine cold.
Don't start it to "just make it home"
If there was steam and the needle hit the max, the problem is still there even after it cools down. The safest option is to tow it to a shop.
Steam or smoke?
Coolant steam is white, disappears quickly in the air, and often smells sweet. It's the most common thing when an engine overheats.
Smoke is different: if it's dark or thick gray, smells burnt, like plastic or oil, or you see flames, don't try to check anything. Get everyone away from the car and call the fire department.
Why does an engine overheat?
Coolant flows through the engine, picks up heat, and releases it in the radiator. When something in that circuit fails, the temperature rises. The most common causes:
Low coolant from a leak
A broken or loose hose, a punctured radiator, a dripping water pump. A colored puddle under the front of the car (green, pink, orange, or blue, depending on the coolant) that smells sweet is a clue. Clear, odorless water is usually from the A/C, and that's normal.
Stuck thermostat
It's the valve that lets coolant into the radiator. If it stays closed, the engine doesn't cool down even if the level is fine.
Radiator fan not turning on
It cools the radiator when the car is moving slowly or stopped. That's why some cars overheat in traffic but not on the highway.
Water pump or belt
The pump circulates the coolant. If it fails, or if the belt that drives it on some engines snaps, the circuit stops.
Clogged radiator
Scale on the inside, or mud, leaves, or bugs on the outside. Air can't get through and heat can't get out.
Figuring out which one it is isn't your job on the shoulder: it's your mechanic's. But arriving with a clear account of what you saw saves diagnostic time, and saves you money.
Once it has cooled down
With the engine cold, check the coolant reservoir (the plastic tank with minimum and maximum marks). If it's empty or very low, there was a loss, and topping up doesn't fix the leak.
Also look under the car and around the hoses: wet spots, dried colored residue, or drips. Take photos: they help your mechanic and Juan.
And watch for one sign: if the oil on the dipstick looks milky, like coffee with milk, don't start the engine again. Coolant may be getting into the oil.
“Tell me what you saw on the dashboard, how long you'd been driving, and whether there are puddles under the car. I'll tell you what's most likely and what to check.”
