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Why Does My Car Overheat While Driving?

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

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Does your car overheat while driving? There are three main things that can cause this problem:

  • Obstructions in the radiator
  • Radiator with some mechanical failure
  • A cooling system component failure

In the following sections, you will find the most common faults that can lead to engine overheating while driving or after repeated hard acceleration.

With a little effort, the help of these sections, and the list of articles in the Resources section at the bottom, you may be able to fix the overheating fault at home.

For this, it's highly recommended you have your car's repair manual to locate components, diagnose faults, and consult the specifications for your particular model.

If you don't already have this manual, get a relatively inexpensive copy through Amazon.

Haynes manuals include:

  • Step-by-step procedures
  • Photographs and illustrations
  • Diagnostic guides
  • Location of parts
  • Replacement of parts
  • Diagrams for the electrical system
  • Maintenance schedule

If you use the manual in your car maintenance projects, you can prevent unnecessary failures and save a lot of money on repairs in the future.

Remember that typically, the normal temperature of an engine can range from 195 F to 220 F (91 C to 104 C). For this, it is necessary for the coolant to circulate properly through the system.

Any interference with the normal circulation of coolant will cause the engine to overheat.

In This Article

1. Obstructed Airflow Through the Radiator
2. Lower Radiator Hose Collapsed
3. Thermostat Failure
4. Faulty Radiator Cap
5. Clogged Radiator
6. Water Pump Impeller Corroded
7. VIDEO: Quick Cooling System Diagnosis
8. Resources

Remove debris from the radiator.

Remove debris from the radiator.

1. Obstructed Airflow Through the Radiator

In some car models, the condenser is located in front of the radiator; other models place them side by side.

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After hundreds of miles of driving, it is common for the front of the radiator, or condenser, or both, to collect bugs, small stones, and other debris.

This reduces airflow through the radiator block, preventing coolant heat from properly dissipating.

Use a radiator fin straightener comb cleaner tool to remove debris from the radiator. The tool is inexpensive, and allows you to remove debris in a matter of minutes.

Also, check the radiator fins for rust and looseness. This type of fault interferes with heat dissipation as well. If necessary, replace the radiator.

Check the lower radiator hose for damage

Check the lower radiator hose for damage

2. Lower Radiator Hose Collapsed

Coolant circulates between the engine and the radiator through two wide diameter hoses.

These rubber hoses can resist vibration, heat, oil, pressure, abrasion, and prevent damage to the radiator. In addition, these hoses can withstand pressure up to six times the cooling system pressure rate.

What's more, the lower radiator hose features an inner wire for better support to resist the suction force of the water pump.

After years of service, though, it is possible for the lower radiator hose to collapse and reduce coolant flow, causing the engine to overheat when the vehicle is in motion.

 A failed thermostat may cause the engine to overheat at cruising speed.

A failed thermostat may cause the engine to overheat at cruising speed.

3. Thermostat Failure

Thermostat failure causes poor cooling system performance. This in turn affects proper engine operation.

If you need to inspect the operation of the thermostat, consult your car's repair manual, and the article on testing the thermostat, listed in the Resources section at the end of this post.

If you need to replace the thermostat, buy one with the same rating as the old one. Starting in 1971, most car engines began using thermostats rated at 192 or 195 degrees.

If you install a thermostat not intended for your application, you will compromise the operation of the ignition, fuel, and emission control systems.

To test and change the thermostat, consult your repair manual. Also, check out the list of articles in the Resources section at the end of this article.

Check the radiator cap seals, valve, and the radiator neck sealing surface.

Check the radiator cap seals, valve, and the radiator neck sealing surface.

4. Faulty Radiator Cap

Inspect radiator cap gaskets and seals for cracks, hardening, or deterioration. Also, check the sealing surfaces of the radiator neck.

After years of service, the spring in the radiator cap weakens, lowering the boiling point of the coolant. This causes the cooling system to transfer fluid to the coolant surge tank before it reaches the proper temperature.

To test the proper operation of the radiator cap, use a pressure tester. You can borrow this tool from your local auto parts store. Consult your repair manual for the radiator cap specifications.

5. Radiator Clogged

Over time, the bottom of radiator tanks fill with rust, slime, dirt, scale, and metal shavings.

It is common for buildup, like mold and scale, to grow inside the cooling system, especially the radiator.

Unfortunately, flushing the radiator can only remove so much buildup. If there are internal blockages, it is better to rebuild or replace the radiator.

To prevent buildup in the cooling system, follow the repair manual recommendations when replacing the coolant and be sure to bleed the air out of the system.

A worn water pump won't circulate coolant at the proper rate.

A worn water pump won't circulate coolant at the proper rate.

6. Water Pump Impeller Corroded

The water pump pulls coolant from the radiator and pushes it into the engine.

As with the rest of the cooling system, buildup can affect the water pump, reducing shaft, impeller, and bearing performance.

In general, it is not common for the water pump to suddenly stop working. Usually, wear can be discovered through noise or coolant leaks.

You can use a mechanic's stethoscope, or a piece of hose, to listen to the water pump when the engine is running. Consult your repair manual. Also, check out the article on water pump diagnostics listed in the Resources section at the end of this post.

7. VIDEO: Quick Cooling System Diagnosis

The following video shows you a simple test drive for a quick diagnose that might work for you if your engine seems to be overheating while driving

8. Resources

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

© 2022 Dan Ferrell

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