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Why Does My Car Overheat in Traffic but Not on the Highway?

4 min readBy the mechanics at Aaron's Auto Repair

The short answer

If your car overheats in traffic but cools down on the highway, the radiator cooling fan is almost always the culprit — a failed fan motor, relay, fuse, or temperature sensor. At highway speed, air rushes through the radiator naturally, so the fan isn't needed.

In this guide

Why speed makes a difference

Moving air does the radiator's job at speed. Stopped in traffic on LBJ in August, only the electric fan moves air across the radiator.

Likely causes

  • Failed radiator fan motor
  • Bad fan relay or blown fuse
  • Faulty coolant temperature sensor
  • Low coolant
  • Clogged radiator fins

Quick check

With the engine warm and AC on, the fan should spin. If it doesn't, the fan circuit is the problem.

Frequently Asked Questions

Turn off the AC and turn on the heater to buy time, but get it fixed soon.

Typically $300–$700 installed.

Yes, 100°F heat pushes cooling systems to their limits.

Need overheating & cooling system repair near you?

Aaron's Auto Repair brings overheating repair to you anywhere within 50 miles of Irving, 24/7 — including Irving, Grand Prairie, Grapevine, Coppell.

Call 469-262-5048

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