Why Is My Engine Overheating? 7 Common Causes and What to Do Right Now

Published Oct 23, 2026 · 7 min read · By Hassan, Owner of Roadmate Services

The temperature needle is the one gauge that never seems to drift up slowly. Why is my engine overheating? Usually low coolant or a leak, a thermostat stuck closed, a cooling fan that has stopped, a failing water pump, or a blocked radiator. Right now: pull over when it is safe, switch the engine off, and leave the radiator cap on.

Below: what to do in the next few minutes, the 7 common causes, why some cars only overheat at idle, and when it is a coolant run or a tow.

Quick answer: overheating causes at a glance

Your car only has one way to say it is too hot, and that needle is it. Take it seriously the first time.

What to do right now if your engine is overheating

Get safe, then call

Signal and pull onto the shoulder, an exit or a parking lot. Turn on your hazards and switch the engine off. On I-70, I-71 or I-270, stay buckled in unless the car is smoking. If you see steam or smoke, get out on the side away from traffic and stay well back from the hood. If anyone is hurt or the car is in a live lane, call 911. Our highway breakdown guide covers the shoulder step by step.

A/C off, heater on full while you find a safe spot

Firestone’s overheating guide says to switch the A/C off and turn the heat to maximum. The heater core works like a small second radiator and pulls some heat away from the engine. It buys a little time to reach a safe spot, not a reason to keep driving. In July it is about the only time a sauna counts as a repair tool.

Never open a hot radiator cap or pour cold water on the engine

The cooling system is under pressure. Open the cap hot and the coolant can spray out boiling. AAA Club Alliance says to wait until everything has cooled, usually 40 to 60 minutes, before touching the cap. Do not pour cold water on the engine either: Firestone warns the sudden temperature change can crack engine parts.

Once it is fully cool: check the coolant reservoir

Look at the see-through plastic coolant tank, not the radiator cap. If the level is below the MIN mark, the car needs coolant, and probably has a leak somewhere. Your owner’s manual names the right coolant type. Look under the car for a green, orange or pink puddle too.

Why is my engine overheating? 7 common causes

1. Low coolant or a leak

The most common cause. Coolant does not get used up like fuel, so a low tank means it went somewhere: a hose, the radiator, the water pump or, at worst, the head gasket. A sweet smell after you park is a clue.

2. Thermostat stuck closed

The thermostat is a small valve that opens to send coolant to the radiator. Stuck closed, it blocks the flow and the engine heats up fast. Larry Carley at aa1car.com notes the giveaway: a hot engine with a cool upper radiator hose. A cheap part with a lot of power over your afternoon.

3. Cooling fan not working

The fan pulls air through the radiator when the car is slow or stopped. An electric fan can fail from a bad motor, relay, fuse or sensor. On older trucks, a worn fan clutch spins too slowly. Either way, the problem shows up first in traffic.

4. Water pump failure

The water pump moves coolant around the engine. A leaking seal, a wobbling shaft or worn impeller vanes slow the flow. Drips near the front of the engine, or a whine or squeal, are common signs.

5. Radiator clogged or damaged

Dirt, leaves and dead bugs can block the air flowing through the front of the radiator, and old deposits can block the coolant flowing inside it. A cracked radiator or a damaged cap lets coolant escape.

6. Collapsed hose or slipping belt

An old lower radiator hose can collapse under suction and choke the flow. A loose or worn belt can slip, so the water pump turns too slowly. A belt squeal followed by a rising needle is worth a stop.

7. Low engine oil

Oil carries heat away as well as lubricating, so Firestone lists low oil as a cause too. Check the dipstick once the engine is cool. If the oil light is on, do not drive.

Engine overheating at idle: why it runs hot in traffic but cools on the highway

At highway speed, air rushes through the radiator on its own. Stopped at a light on Broad Street, the cooling fan has to do all of that work. So if your engine overheats at idle and cools down once you get moving, the fan side is the first suspect. As aa1car.com puts it, the fan must turn fast enough to cool the engine at idle and low speed.

• Electric fan that does not switch on, from a bad fan motor, relay, fuse or temperature sensor.
• Worn fan clutch on rear-wheel-drive trucks and SUVs.
• Missing or broken fan shroud, so the fan pulls less air.
• Low coolant, which often shows up first when there is no airflow to hide it.
• A radiator front packed with bugs and debris.

A quick test once the engine is warm: with the A/C on, the electric fan should run. If it never spins, tell your mechanic. Some cars only panic in traffic, just like their drivers.

What overheating can do to an engine

A short spike caught early often does no lasting harm. Driving on with the needle in the red is a different story. Heat can make the cylinder head swell and crush the head gasket, and in bad cases damage the pistons, as aa1car.com explains. Signs of a blown head gasket include white exhaust smoke and coolant that keeps disappearing with no visible leak.

The fix is simple: stop early. A few minutes on the shoulder is cheaper than a head gasket by a wide margin.

Coolant delivery or a tow?

Not everything is a roadside job, and we will say so. If the tank is simply low and the engine has cooled, we can bring coolant. We bring the type you ask for, bought for your call. Not sure which type? We work it out from your VIN. The technician can top it up for you or hand it over, whichever you prefer.

It is a tow to a mechanic when:

• Coolant is pouring or dripping out, or the tank empties again soon after a top-up.
• The belt is broken, the water pump is leaking, or a hose has split.
• Steam keeps coming after the engine is off, or the exhaust smoke is white and heavy.
• The oil light is on, or the engine knocks.
• It overheats again within a few miles.

A jug of coolant cannot replace a water pump, however hopeful we all are. If the car will not start at all after it cools, see our car won’t start guide, or our tow truck vs roadside assistance comparison if you are not sure which to ask for.

What it costs in Columbus: tow $125 to $275, coolant quoted by phone

• Tow to a mechanic: $125 to $275, estimated, for tows of about 1 to 15 miles. Longer tows are quoted by phone.
• Coolant delivery: quote by phone, because the price depends on the coolant your car needs.

The final price depends on your exact location, the vehicle and conditions on scene. A dispatcher tells you the price and an arrival estimate before anyone heads your way. Our tow cost guide explains what moves a tow price, and the tow service in Columbus page has the details.

5 things to check so your engine does not overheat

1. Look at the coolant reservoir once a month, engine cold. It takes a few seconds.
2. Watch the temperature gauge for a week and learn where it normally sits.
3. Check under the car where you usually park for colored drips.
4. Have hoses and belts looked at during oil changes, especially on older cars.
5. Keep a jug of the right coolant in the trunk. Our emergency car kit list has the rest.

Coolant is quick to check and very slow to forget once it runs out.

Frequently asked questions

More coolant guides: is coolant the same as antifreeze; how to add coolant; car leaking coolant; low coolant symptoms; what color is coolant.

The bottom line

Most engines overheat because of low coolant, a stuck thermostat, a dead fan, a failing water pump or a blocked radiator. Pull over safely, switch the engine off, and never open a hot radiator cap. If it is only low coolant, a top-up can get you to a shop. Anything more is a tow to a mechanic.

Here is to a temperature needle that stays bored, right in the middle.

Related: jump start service in Columbus for a different kind of roadside stop.