Car overheating? Turn off the A/C, turn the heater and fan to full hot, and pull over as soon as it’s safe. Shut the engine off and let it cool. Never open the radiator cap while the engine is hot. The most common causes are low coolant from a leak, a stuck thermostat, a failing water pump, a clogged radiator or a cooling fan that isn’t working.
Quick answer
- Right now: A/C off, heater on full hot, pull over safely, engine off.
- Never open a hot radiator cap or pressurized coolant tank. Hot coolant can spray and burn you.
- Stop driving if the gauge is in the red, a temperature warning light is on, or steam is coming from under the hood.
- Common causes: coolant leak, thermostat, water pump, radiator, cooling fan or a broken belt. Head gasket failure is less common but serious.
- For a tow, call (301) 762-1200. We offer 24-hour emergency towing.
What should you do when your car starts overheating?
The moment the temperature gauge climbs past its normal spot, or a red temperature light comes on, act fast. A few minutes can be the difference between a simple repair and a damaged engine.
- Turn off the A/C. The air conditioning adds load and heat to the engine.
- Turn the heater to full hot and the fan to high. It feels miserable in summer, but the heater core acts like a small second radiator and pulls heat away from the engine. Roll the windows down.
- Pull over as soon as it’s safe. Get off the road, put the hazard lights on, and shut the engine off.
- Don’t open the hood if steam is pouring out. Wait until the steam stops. Once it’s safe, opening the hood helps the heat escape.
- Let it cool for at least 30 minutes. Often longer. Don’t pour cold water on a hot engine.
- Call for help if the gauge was in the red, you saw steam, or you can see coolant leaking.
Never open the radiator cap or a pressurized coolant tank on a hot engine. The system is under pressure, and the coolant is well above boiling. Opening it can spray scalding coolant on your face and hands.
What causes a car to overheat?
- Low coolant from a leak: the most common cause. Leaks come from hoses, the radiator, the water pump, the heater core or a loose clamp. You may see green, orange or pink fluid under the car, or smell something sweet.
- Stuck thermostat: the thermostat opens to let coolant flow to the radiator. If it sticks closed, the engine can overheat quickly, often within a few miles of starting.
- Failing water pump: the pump moves coolant through the engine. Signs include a leak or drip near the front of the engine, a whining or grinding noise, and overheating.
- Clogged or damaged radiator: old coolant, debris or corrosion can block the radiator inside, and leaves or bugs can block it outside.
- Cooling fan not running: a bad fan motor, relay, fuse or sensor. This usually shows up in traffic, when the car isn’t moving air through the radiator on its own.
- Broken drive belt: on many cars the same belt drives the water pump. If it snaps, the engine can overheat fast, and the battery light may come on too.
- Head gasket failure: less common, and often the result of earlier overheating. See the signs below.
A useful clue: if the temperature climbs in stop-and-go traffic but drops back when you get moving, the cooling fan is a likely suspect. If it climbs at highway speed, look more at coolant level, the thermostat, the water pump or the radiator.
What are the signs of a blown head gasket?
A head gasket seals the engine block to the cylinder head. Overheating can damage it, and a damaged head gasket can also cause overheating. Common signs include:
- Thick white exhaust smoke with a sweet smell
- Coolant disappearing with no visible leak
- Bubbles in the coolant reservoir with the engine running
- Milky, light brown residue on the oil dipstick or under the oil cap
- Repeated overheating, rough running or misfires
Some of these can have other causes. A little milky residue under the oil cap can come from condensation on short trips, for example. A mechanic can confirm with a pressure test or a combustion gas test. Head gasket work falls under engine repair, and catching it early limits the damage.
Is it safe to drive an overheating car?
No, not while it’s overheating. Driving with the gauge in the red can warp the cylinder head, blow the head gasket or seize the engine. Those repairs cost far more than a tow.
If the engine overheated briefly, cooled down, and the coolant level is fine once cold, a short, gentle drive to a shop is sometimes possible. Watch the gauge the whole time and stop again if it climbs. If you have to top off, use the coolant type your owner’s manual lists. In an emergency, plain water can get you to a shop, but the system should be flushed and refilled with the right mix afterward. If you saw steam, lost a lot of coolant, or the car overheats again within minutes, don’t drive it. Call us for 24-hour emergency towing at (301) 762-1200.
Why do cars overheat more in Maryland summer traffic?
Maryland summers are hot and humid, and stop-and-go traffic on I-270, the Beltway or Rockville Pike means very little air moves through the radiator. The cooling fan has to do all the work while the A/C adds extra load. A cooling system that seems fine on a spring drive can give up on a 95-degree afternoon in traffic. Low coolant, a weak fan or an old radiator usually shows up first in these conditions. Having the cooling system checked before summer can save you a breakdown in traffic.
What can you check yourself safely?
- Coolant level, engine cold only. Check the see-through reservoir. The level should sit between the MIN and MAX marks.
- Puddles. Green, orange or pink fluid under the front of the car, especially with a sweet smell, is coolant. Clear water on a hot day is usually normal A/C condensation.
- Hoses. With the engine cold, look for wet spots, cracks or crusty residue around hoses and clamps.
- The fan. On many cars the electric fan runs when the A/C is on. Keep hands, hair and clothing clear, because an electric fan can switch on even with the engine off.
- Clean up spills. Coolant tastes sweet and is poisonous to pets and children.
If a scan tool is needed to check fan circuits or temperature sensor readings, computer diagnostics can pinpoint the fault.
Engine running hot?
Our ASE-certified mechanics pressure-test the cooling system, find the leak or failed part, and fix it before it damages the engine.
Car overheating FAQ
What should I do first if my car overheats?
Turn off the A/C, turn the heater and fan to full hot, and pull over as soon as it’s safe. Turn the engine off and let it cool for at least 30 minutes before checking anything.
Why does turning on the heater help an overheating engine?
The heater core is a small radiator inside the dashboard. With the heater on full hot and the fan on high, it pulls extra heat out of the coolant.
Can I just add water to an overheating car?
Only once the engine has cooled, and only in an emergency. Water can get you to a shop, but the cooling system needs the right coolant mix, and a car that is losing coolant has a leak that needs to be found.
How long should I wait before opening the radiator cap?
Wait until the engine is fully cool, usually at least 30 minutes and often longer. If the upper radiator hose still feels hard and hot, the system is still under pressure.
Why does my car overheat only in traffic?
At low speed, the cooling fan provides nearly all the airflow through the radiator. Overheating in traffic that goes away on the highway often points to a fan, fan relay or fan sensor problem.
Bring your car to New Level Auto Service
We’re at 716 E Gude Dr in Rockville, MD. Walk-ins are welcome, and calling ahead gets you in faster.
- Phone (301) 762-1200
- Hours Monday to Friday 8 AM to 5 PM, Saturday 9 AM to 2 PM
- Extras Night drop and 24-hour emergency towing