Car Won’t Start Until It Cools Down

Most no-start situations we experience occur during cold mornings, especially when the battery is weak. After running the engine for a couple of minutes, it becomes easy to start. But when the car won’t start until it cools down, you have something wrong that needs to be addressed quickly.

But what could be the problem if a car struggles to start when hot or won’t start? This article will provide in-depth information about all the possible reasons that my colleague, Tochi Emmanuel, and I have experienced over the years as experienced mechanics. By the end, you will know the possible causes and best solutions to this problem.

car won t start unless i wait

What causes a car not to start when it is hot?

The most common reason a car won’t start until it cools down is a faulty crankshaft or camshaft position sensor and a bad fuel pump. If a bad camshaft is the cause, the engine will run fine until you off it. But if the engine stalls and shuts by itself when hot and won’t start until it cools down, you have a bad fuel pump.

However, there are other possible causes, such as clogged air filters, vapor locks, defective starter motors, lousy ground connections, and bad battery connections. Let’s look in-depth and see how this could be why your car won’t start after driving a long distance.

Faulty crankshaft and camshaft position sensor

The camshaft and crankshaft position sensor are responsible for monitoring the rotation of the camshaft and crankshaft. These sensors forward this information to the powertrain control module, which uses the data to adjust the firing of the spark plugs for optimal engine performance.

If any of these sensors become faulty, there will be an incorrect or no signal to the powertrain control module, especially when the engine is hot. This will cause intermittent operation that could shut off the engine and prevent it from starting until it cools down.

Lousy fuel pump

The fuel pump sends petrol from the fuel tank to the engine. And without it, you can’t start the vehicle. The fuel pump keeps running once you start up the engine, whether you are driving or at a standing point. Due to this continuous stress, it’ll eventually become weak and fail.

One of the common signs of a failing fuel pump is that it will become hot after covering a long distance and won’t supply the appropriate amount of fuel to the engine. This will lead to power surges, loss of power, engine misfire, sputtering, and dead engines. As the engine gets hot, whether you turn it off or it shuts off by itself, it won’t start until it cools down. You have a lousy fuel pump if your car won’t start right after turning off.

Clogged air filter

The air filter is a maintenance item that gets replaced or cleaned at every routine vehicle maintenance. It is responsible for filtering the air that goes into the engine. As a result, it gets clogged over time and needs cleaning or replacement.

However, some people forget to clean it during oil changes, letting it clog with dirt, debris, and other particles. When blocked, it won’t allow enough air into the engine. This will throw off the predefined air-fuel ratio for optimal performance. While this will rarely cause the engine to shut off, it may cause a car hard to start after sitting for 30 minutes or so.

Loose battery connection

As you drive into road bumps rocky roads, or as the car vibrates, the battery terminal will wiggle and eventually become loose. Also, the terminals can corrode over time and cause power issues. Loose battery connection problems can happen when the engine is cold, but it is more prevalent when it is hot. If battery connections are the root cause, you will notice electrical and electronic components issues.

Defective starter

Every car starter features a motor inside. That’s why it is often called a starter motor. The motor can wear out over time and struggles to start the vehicle. This happens both when the engine is cold and warm. But in some cases, especially at the early stage, the issue will be evident when the engine is warm. If your car won’t crank when engine is hot, you have a defective starter motor.

If you hear a grinding, whining, or clicking noise when starting the vehicle, that’s a notable indicator that the starter is the culprit.

Bad ground connection

Engine ground is needed for efficient engine and electrical system operations. If the engine ground connection becomes rusted or loose, it will increase circuit resistance. The starting and other system components will be affected. When this happens, it may prevent the car from starting and cause the transmission and electronic components to start acting funny.

Defective engine coolant temp sensor

The coolant temperature sensor measures the engine temperature through the coolant and relates this information to the powertrain control module. If the sensor goes bad, it can send incorrect information to the car computer, telling it that the vehicle temperature is too high.

The car computer works with the information received from the coolant sensor to fine-tune the engine operation. If the temperature sensor is faulty, it can augment the engine temperature reading, and the PCM will prevent the car from starting thinking the car is extremely overheating.

Fuel vapor lock

Fuel vapor lock issues are common with vintage and classic cars because they feature mechanical fuel pumps instead of the electric pumps in newer modern cars. Why this happens mostly on cars with mechanical pumps is because these pumps heat up more than the electric pumps.

Typically, mechanical fuel pumps heat up along with the engine. And as the pump heats up, the fuel evaporates and stops the flow. If the car shuts off or you turn it off, it won’t start until you allow the engine to cool down for some time. If your car has trouble starting after being driven for long, you likely have a fuel vapor lock.

However, if this happens constantly, you are likely not dealing with a fuel vapor lock. It could be a lousy crankshaft or camshaft sensor or faulty fuel pump.

Why does my car cut off when hot and start when it cools down?

The most prevalent reasons for a car to stall, misfire, and eventually shut off when hot and only start when it cools down are faulty crankshaft or camshaft position sensor, bad fuel pump, fuel vapor lock, and lousy engine coolant temperature sensor. Other possible reasons include a lack of spark and PCM issues on EFI cars.

How do you fix the problems?

The best way to resolve this problem is to identify the root cause first and fix or replace the faulty component. My rule of thumb is to always start with the most common cause and the easiest to fix.

Check the battery connections.

I get it. Bad battery connection is not the most common cause. But it is the easiest to fix. Wiggle the battery cables and see if they are properly tightened. If they are not, tighten them. That could be all you need to address the underlying issue. Check the battery terminal for corrosion. If the terminals or cables are corroded, clean them with a wire brush and baking soda.

Unclog the air filter

Disconnect the air filter housing and inspect the filter. Unclog it if it is mildly blocked by blowing compressed air through it. But if it is completely clogged, the best solution is to replace it.

Replace the lousy fuel pump.

In most cases, a lousy fuel pump is the reason a car won’t start then starts later. Drop the gas tank and remove the fuel pump. Test the pump to see if the pressure is okay. If the pressure is weak, you have a lousy fuel pump that needs replacement. Replace the pump and mount the gas tank.

Replace lousy camshaft or crankshaft position sensor

Check if the crankshaft or camshaft position sensor is faulty by performing a resistance test or bench test. But before performing any of these tests, diagnose the vehicle with a scan tool.

If the scan tool does not pull out a bad crankshaft or camshaft position sensor code, the sensor is not the problem, and there’s no need for the test. But if it does, perform the above tests for reconfirmation. If the test says you have a bad CMP sensor, replace the sensor.

Contact your mechanic

If you can’t resolve the problem yourself, the next option is to contact your local mechanic. The mechanic will perform a thorough diagnosis and proffer a solution to the underlying problem.

Final Words

If your car overheats before shutting off and won’t start until it gets cooled again, the problem and possible solutions are far-fetched from what I listed above. This article does not cover any information related to car overheating.

In summary, the most common reasons your car won’t start until it cools down are a faulty camshaft or crankshaft position sensor, a bad fuel pump, a fuel vapor lock, bad ground, loose battery terminals, and a blocked fuel pump.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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