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Steam rising from under the hood of an overheating car pulled over on the side of the road

Cooling System

Why is my car overheating? Seven causes and what they cost to fix

6 min read

Engine overheating is the kind of problem where the wrong reaction makes a $400 repair into a $4,000 repair. Pull over the second the gauge climbs. Here are the seven most common causes, what to do in the moment, and what each one costs.

First, do this immediately

  1. 01Pull over safely. Get off the highway, find a parking lot.
  2. 02Turn the engine OFF. Do not idle it 'just to keep the AC on.'
  3. 03Pop the hood from inside the car. Do not approach the engine yet.
  4. 04Wait at least 20 minutes before opening anything. The radiator is under high pressure when hot, and a hot radiator cap removed early can cause severe burns.
  5. 05Call us at (972) 231-2886 or call for a tow. Driving an overheating engine costs head gaskets in minutes.

The seven most common causes, by frequency

These are the causes we see in our Richardson bays, ordered roughly by how often they show up.

1. Low coolant

Coolant has leaked out, evaporated, or was never properly refilled after the last service. The system runs out of fluid to carry heat away. Cost to refill: $20 to $60 if there is no underlying leak. Cost to find and fix the leak: $100 to $400 depending on the source.

2. Failed thermostat

The thermostat regulates coolant flow based on temperature. When it fails closed, coolant cannot circulate and the engine overheats fast. Replacement: $220 to $500 depending on access.

3. Water pump failure

The pump drives coolant through the engine. When the impeller breaks or the bearing seizes, coolant stops flowing. Replacement: $450 to $1,200 depending on whether it is timing-belt driven.

4. Cooling fan or fan relay

At low speeds, the electric fan pulls air through the radiator. If the fan motor or its relay has failed, the engine overheats in stop-and-go traffic but cools down on the highway. Cost: $250 to $700.

5. Clogged or failing radiator

Internal corrosion or external damage. Replacement runs $500 to $1,200 including labor and a fresh coolant fill.

6. Burst or split hose

Rubber cooling hoses get brittle in Texas heat over years. A burst hose dumps coolant in seconds. Hose replacement: $150 to $400.

7. Head gasket failure

The serious one, usually the result of overheating that was driven through. Combustion gases enter the cooling system, coolant enters the cylinders. Repair: $1,800 to $3,500. This is why we say pull over.

Why summer is the season this happens

100°F+ ambient temperatures, AC running constantly, and stop-and-go traffic on 75 are the perfect storm for cooling systems. Marginal hoses fail, marginal thermostats stick, marginal water pumps quit. If your system is over 60,000 miles since the last flush, get it checked in spring before August has the final word.

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