Car Won’t Start When Parked In The Sun: 9 Reasons With Easy Cures

On a sweltering hot day, your car bakes in the sun while you work or run errands, and as you return anticipating a cool escape, you’re greeted with an unexpectedly stubborn engine that refuses to start.

Exasperating and perplexing, this inconvenient scenario leaves countless motorists scratching their heads.

Understanding why your car won’t start when parked in the sun is crucial, as the consequences range from simple delays to potential expensive damage.

As temperatures soar, certain components in your car become vulnerable, and these heat-related issues can prevent the engine from firing up.

Car won't start when parked in the sun

This article will delve into the root causes of this problem, examining the vital parts susceptible to high temperatures and outlining preventative measures.


Why Car won’t start when parked in the sun?

Taking these preventative measures and understanding the reasons behind a car won’t start when parked in the sun can minimize the chances of being stranded on hot summer days.

Car won't start when parked in the sun

Heat-Induced Fuel Problems

One of the main reasons cars might not start when parked in the sun is heat-induced fuel issues. High temperatures can cause fuel to vaporize within the fuel lines and pump.

This process, known as vapor lock, restricts fuel flow to the engine and prevents it from starting. The good news is that vapor lock is often temporary and can be resolved once temperatures drop.


  • Allow time for the car to cool down in a shaded area or wait until outdoor temperatures drop before trying to start again.
  • Insulate your fuel lines to protect them from extreme heat.
  • Consider using fuel additives to lower the fuel’s vaporization point.

Failed Starter Motor due to High Temperatures

The starter motor is sensitive to heat; particularly high temperatures can overwhelm or damage this component. A heat-damaged starter motor might struggle to turn over the engine, resulting in a car that won’t start when parked in the sun.


  • Give your vehicle time to cool down. Once the temperature of the engine compartment has decreased, attempt to start your car again.
  • Conduct regular maintenance and inspection of your starter motor, replacing it if necessary.
  • Maintain proper ventilation and airflow within the engine bay.
  • Heat shields protect your starter motor from excessive heat.

Malfunctioning Coolant Temperature Sensor

A faulty coolant temperature sensor (CTS) might be the culprit behind your car’s starting troubles when parked in the sun. The CTS provides important information to the engine control unit about the coolant’s temperature, influencing fuel mixture and ignition timing.

If the sensor malfunctions, it could send inaccurate readings, leading to ignition and fuel delivery issues.


  • Regularly inspect your coolant temperature sensor and check for signs of wear or damage.
  • Test the sensor’s functionality and replace it if necessary.
  • Monitor your dashboard temperature gauge for sudden or erratic changes, which could indicate a faulty CTS.

Maintaining Proper Coolant Levels

Another reason your car may have issues starting while parked in the sun is due to low or deteriorated coolant levels. Over time, coolant can become contaminated over time or lose effectiveness, leading to insufficient cooling.


  • Periodically check your car’s coolant levels, ensuring they remain within the appropriate range.
  • Conduct regular coolant flushes to replace the old or contaminated coolant, following your vehicle’s service schedule.
  • Inspect your radiator and hoses for signs of leaks or damage, repairing or replacing as necessary.

Overheating Starter Relay

Extreme temperatures can also affect your car’s starter relay, which is a crucial component for powering your starter motor. High temperatures may cause the starter relay to overheat, preventing it from operating correctly and leaving you with a car that won’t start.

Overheating Starter Relay


  • Allow your engine to cool before starting your car again.
  • Locate and inspect the starter relay for signs of damage and replace it if necessary.
  • Ensure your vehicle’s electrical system is clean and corrosion-free, as this could contribute to a bad starter relay.

Overdue Oil Change Impacting Engine Performance

Skipping regular oil changes can lead to many car problems and, in some cases, may even contribute to your car’s reluctance to start when parked in the sun. Over time, oil can become contaminated and lose viscosity, compromising the engine’s performance and impacting its ability to start.


  • Stick to your vehicle’s recommended oil change schedule in the owner’s manual.
  • Choose the right grade of oil for your car, as using improper oil can affect its performance, especially in extreme temperatures.
  • Regularly monitor your engine’s oil levels, looking for any unusual oil consumption or leaks.

Heat-Affected Battery Problems

High temperatures can adversely impact your car’s battery, causing many issues, including starting problems. Heat can cause the battery fluid to evaporate, which may lead to internal damage and a shortened battery life.


  • Keep the battery clean and corrosion-free, which can help reduce heat build-up.
  • Regularly inspect the battery terminals, ensuring they are clean and tight.
  • Properly shield the battery from excessive engine heat using heat barriers or insulation.
  • Have your battery tested periodically, particularly during hot weather, and replace it when necessary.

Heat-Affected Ignition System

Ignition systems components, such as spark plugs, ignition coils, or distributor caps, can be sensitive to high temperatures. Excessive heat may cause these components to expand or warp, temporarily disrupting their functionality and resulting in starting issues.


  • Keep up with your vehicle’s recommended maintenance schedule, replacing worn or damaged ignition system components as needed.
  • Install heat shields for sensitive ignition components if recommended for your vehicle.
  • Ensure proper airflow in the engine bay to help dissipate heat and protect engine components.

Expanding Car ECU causing starting problems

Extreme heat can cause the car’s engine control unit (ECU) to expand, potentially disrupting its internal connections. This expansion can compromise the ECU’s proper functioning, creating various issues, including failure to start.


  • Ensure the ECU is securely fastened and protected from excessive heat.
  • Install a reflective heat shield or insulation around the ECU to help protect it from high temperatures.
  • If the ECU continues to malfunction despite these precautions, it may need to be repaired or replaced by a professional mechanic.

What to do if your car won’t start in the heat?

If your car won’t start in the heat, here are some troubleshooting steps and solutions you can try:

What to do if your car won't start in the heat
  1. Check for a clogged air filter: A dirty air filter can restrict airflow to the engine, causing starting issues.
  2. Inspect battery terminals and cables: Corroded or loose battery terminals can cause starting problems. Ensure they are clean and secure.
  3. Check the engine ground connection: A corroded or loose engine ground connection can lead to starting difficulties.
  4. Address vapor lock: Vapor lock occurs when fuel vaporizes within the fuel system due to high temperatures. Allow your car to cool down or add a fuel additive to reduce vapor lock.
  5. Examine your fuel system: Leaks in the fuel pressure regulator or injectors can cause hard starting. Inspect these components and repair or replace them if needed.
  6. Test the starter motor and circuit: A malfunctioning starter motor or circuit can make your car hard to start in extreme heat.
  7. Cool the engine: If your car doesn’t start after being parked in the sun for an extended period, wait for the engine to cool down before restarting. You can also add coolant to your car, but only when the engine has cooled down.

Suppose your car still doesn’t start after trying these steps. In that case, it’s advisable to take your vehicle to a mechanic, as there could be an underlying issue exacerbated by the heat, such as a problem with the starter or other engine components.


In conclusion, the issue of a car not starting when parked in the sun can be attributed to various reasons. Understanding these causes and taking preventative measures is the key to ensuring your vehicle remains reliable during hot summer days. Some common reasons include:

  • Extreme heat causing battery issues
  • Vapor lock in the fuel system
  • Ultraviolet radiation affecting electronic devices

To combat these issues, car owners can take several practical steps:

  1. Park in a shaded area or utilize sunshades to protect the interior and dashboard
  2. Regularly check and maintain both the battery and fuel systems
  3. Consider using a solar-powered ventilator to keep temperatures down inside the vehicle

By keeping these points in mind and taking preventative measures, car owners can reduce the likelihood of being stranded with a vehicle that refuses to start after being parked in the sun.

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