What Causes a Car to Overheat, and What Should You Do?
You’re driving along when the temperature gauge starts creeping toward red. An overheating engine is one of the few car problems where what you do in the next few minutes really matters. Here is what usually causes it, what to do right away, and when to have it checked.
Quick Answer: Why Is My Car Overheating?
Cars usually overheat from low or leaking coolant, a failing thermostat, a bad water pump, or a blocked radiator or cooling fan. If the gauge climbs into the red, turn off the AC, turn on the heater to pull heat from the engine, and pull over safely to let it cool, then shut off the engine; do not open a hot radiator cap. Continuing to drive a badly overheating engine is one of the fastest ways to cause permanent damage, so have it diagnosed promptly.
What to Do When Your Car Overheats: Step by Step
Step 1: Turn off the AC and turn on the heat
Switch off the air conditioning to take load off the engine, then set the heater and fan to maximum. It will be uncomfortable, but the heater core pulls heat away from the engine.
Step 2: Pull over safely and shut off the engine
Signal, move out of traffic to a safe spot, put the vehicle in Park, and turn the engine off. Turn on your hazard lights.
Step 3: Let the engine cool before opening anything
Do not open the radiator cap or coolant reservoir while the engine is hot. The system is under pressure and hot coolant can cause serious burns. Wait until the hood and engine are cool to the touch.
Step 4: Check the coolant level
Once the engine is cool, check the coolant reservoir. If it is low, top it up with the coolant type specified in your owner’s manual, and look under the vehicle for drips or puddles.
Step 5: Get it diagnosed before driving far
Even if the gauge returns to normal, overheating has a cause that needs to be found. If the gauge climbs again, you see steam, or coolant is leaking, do not keep driving; arrange a tow to a service center.
Common Causes of Car Overheating
Most overheating comes down to the cooling system not moving enough coolant, or not shedding enough heat. The symptoms usually point to the cause:
| What you notice | Likely cause | What to do |
|---|---|---|
| Low coolant reservoir, puddles under the car, or a sweet smell | Coolant leak or low coolant | Top up when cool, then have the leak found and repaired |
| Temperature climbs quickly after starting, and the heater may blow cool air | Thermostat stuck closed | Have the thermostat tested and replaced if needed |
| Whining or grinding from the front of the engine, or coolant dripping near the pump | Failing water pump | Stop driving and have the pump inspected promptly |
| Overheats in traffic or at idle, but cools down at highway speed | Cooling fan not working | Have the fan, its relay, and wiring checked |
| Overheats at highway speed or while towing | Clogged or damaged radiator | Have the radiator inspected and the cooling system serviced |
| Coolant pushing into the overflow tank, or hissing around the cap | Faulty radiator cap | Have the cap pressure-tested and replaced if needed |
How to Prevent Overheating in Gulf Coast Heat
- Check coolant regularly. Look at the reservoir level when the engine is cold, especially before a long summer road trip.
- Keep up with scheduled maintenance. Coolant, hoses, and belts are checked during routine service.
- Watch the gauge in traffic. Long idles with the AC running are when a weak fan or low coolant shows up first.
- Do not ignore small leaks. A slow leak today is an overheated engine on the next hot afternoon.
Frequently Asked Questions: Car Overheating
What causes a car to overheat?
The most common causes are low or leaking coolant, a thermostat stuck closed, a failing water pump, a cooling fan that is not working, and a clogged radiator or faulty radiator cap. Each one keeps the cooling system from moving or shedding heat the way it should.
What should I do if my car overheats?
Turn off the AC, turn the heater to maximum, pull over somewhere safe, and shut off the engine. Let it cool completely before opening the hood or checking coolant, and never open a hot radiator cap. Then have the cooling system diagnosed before driving far.
Can I keep driving an overheating car?
It is not a good idea. Driving with the gauge in the red can warp engine parts and blow the head gasket, turning a small cooling-system repair into a major one. If the temperature will not stay down, have the vehicle towed.
Why does my car overheat when the AC is on?
The AC adds load to the engine and sends extra heat through the condenser in front of the radiator. If the cooling fan is weak, coolant is low, or the radiator is partly clogged, the extra load can be enough to push the temperature up, especially in stop-and-go traffic.
Can low coolant cause overheating?
Yes. Low coolant is one of the most common causes. Without enough coolant, the system cannot carry heat away from the engine. Coolant does not get used up in normal driving, so if the level keeps dropping, there is a leak that needs to be found.
Related Maintenance Tips
- Radiator problems and leaking coolant
- Why car AC compressors fail, and how to prevent it
- All Mercedes-Benz service and maintenance tips
When to See a Mercedes-Benz Technician Near Fort Walton Beach
If your temperature gauge climbs, a coolant warning appears, or you keep topping up coolant, have it checked before the next hot drive. The factory-trained technicians at Mercedes-Benz of Fort Walton Beach can pressure-test the cooling system, find the cause, and tell you exactly what your vehicle needs. We serve drivers across Fort Walton Beach, Destin, Niceville, and the Emerald Coast.
Schedule service online or check our current service specials.
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