The engine doesn’t start when hot. What are the causes?

The car engine may experience hard starting or does not start at all when outside temperatures are high. There are a few parts or situations that can lead to this problem which we can cover below.

Why engines don’t start when the weather is hot?

First of all, you need to know that the engine sensors are directly responsible for the fact that the engine does not start on hot summer days. You should consider also checking the quality of your fuel because this is a common cause of why engines have starting issues when ambient temperatures are high.

  • If the crankshaft position sensor is bad or failing, this can lead to sending wrong data to the Electronic Control Unit, data that the ECU might consider issues and will prevent the engine from starting. This is usually signaled by dashboard errors, so it’s better to scan using OBD II
  • The same can be said about the coolant temperature sensor. If this sensor fails, it will also give incorrect info to the Electronic Control Unit (ECU), that, in most cases, think that the temperature is above normal and cause the engine not to start in the ambient conditions above.
  • Especially on petrol cars, because of high temperatures outside, fractions of gasoline evaporates, forming a rich fuel mixture that causes the engine not to start.
  • A bad or failing fuel pump. Especially on petrol engines, a bad fuel pump can be responsible for the engine not to start in warm temperatures
  • A bad mass air flow sensor. A malfunctioning MAF sensor can also lead to a hard engine start in warmer ambient because the tasks assigned to a bad MAF sensor can’t be done properly anymore and you should change it.
  • A failing idle speed sensor can also cause the engine to barely start or not start at all in warmer temperatures.
  • Ignition problems are also responsible for a hard or no engine start. These problems can be due to problems with the starter motor or circuit. The starter has some brushes that wear out over time naturally and adding excess heat, can lead the engine not to start.
  • A faulty fuel pressure regulator
  • A bad or failing high-pressure pump. Because air enters the pump, it will be impossible to achieve operating pressure.

Poor quality fuel is responsible for a rich fuel mixture that forms fuel vapors. Consider changing the fuel you use for a period of time to see if there are improvements when starting the engine.

What about engine stalling when it is hot?

The reason why the engine may stall when reaches the normal operating temperature lie especially in the fuel you use. If you use a low-quality fuel, problems can occur shortly after you pour bad diesel or gasoline in your engine. You will see that the car shakes, jerks, and eventually stall. You should remove all the fuel from the tank, replace the fuel filter.

When the engine is warm it can stall because of a bad or clogged fuel filter and also a clogged air filter. The engine can “choke” with the rich mixture and stall shortly after starting.

Also as in the case with high temperatures, a warm engine can stall because of a bad or failing fuel pump.

Another reason why warm engine stalls is a failing alternator. If it’s damaged, an alternator will no longer charge the battery, and, increased engine temperatures will rush the charging problem. You may not see this quickly, but after the battery is drained and you can’t start the engine after that.

Tips for starting the engine in hot temperatures.

If the temperatures outside are high, or for some reason you left the car sitting under a hot sun for a certain amount of time and the engine does not want to start, you should first try adding a good quality fuel.

Removing the current fuel from the tank helps a lot, but if you can’t do that, you can fill up the tank, open the throttle valve by pressing the gas pedal or remove the filter cover and let the fuel vapors dry for 5-10 minutes. After that, try starting the engine, if this does not work, you will have to perform a detailed check for the parts above.

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