Car Won’t Start After Overheating: Here’s What You Might be Missing!

So, you just noticed that the temperature gauge on your car dashboard is creeping up, or the telltale steam coming out from under the hood. When your engine overheats, it can cause a slew of issues, including a stalling car or one that won’t start at all.

In this article, we’ll discuss why your car won’t start after overheating and offer practical solutions to get back on the road.

So, why car won’t start after overheating? A common reason a car won’t start after overheating is a blown head gasket. Overheating can damage the engine’s internal components like pistons and bearings, preventing it from starting. Overheating can also damage electrical systems like the battery, starter or alternator, or melt wires and blow fuses, preventing the car from starting. Regular coolant and radiator hose inspection helps avoid overheating. After overheating, check coolant levels, electrical systems, and engine components to determine and repair the cause.

Also Read: My car sometimes starts and sometimes it doesn’t

First Hand Approach When Car Won’t Start

Here are some of the things you should do when your car won’t start:

1. Check OBD2 Codes

When your car won’t start, it can be a frustrating and overwhelming experience. However, taking a first-hand approach and diagnosing the issue yourself can save you time and money in the long run.

One of the first things you should do when your car won’t start is to check what error codes are stored in the ECU memory. The ECU (Engine Control Unit) is the computer that controls many of the car’s key systems, and it stores error codes that can help diagnose the issue.

To check for these error codes, you will need an OBD2 scan tool. A recommended scan tool is BlueDriver. This device can be plugged into the OBD2 port of your car, which is often located under the dashboard of the driver’s side. Once plugged in, turn on the ignition of your car.

You don’t have to start the car to check for trouble codes. If the ignition system is functioning correctly, this method will work.

By scanning for trouble codes, you can get a better understanding of what is causing your car not to start. The scan tool will provide you with a list of codes that can help diagnose the problem.

Sometimes, your car needs multiple ignition cycles to show trouble code as I mentioned in my guide on check engine light with no codes.

2. Check Coolant or Engine Oil Color

coolant and oil mix when head gasket blows

One common reason for an overheated engine is a problem with the coolant system. When this happens, it’s important to let the engine cool down completely before attempting any inspection.

Once the engine is cool, you can visually inspect the coolant color by opening the radiator cap. The coolant color should be a bright and clear color, depending on the type of coolant being used by your car.

If the coolant color appears milky brownish, then it indicates a clear sign of a serious issue. The milky color means that coolant and oil have mixed together, which could be due to a blown head gasket.

The head gasket sits between the engine block and the cylinder head, and its function is to prevent oil and coolant from mixing. However, if the head gasket is damaged or not working properly, it can allow the two fluids to mix. This mixing can cause a milky brownish color in your coolant.

Also, if your engine is producing white smoke from exhaust, it indicates that coolant is burning in the engine due to leakage through the head gasket.

Similarly, if you open the oil filler cap, and observe milky color of oil, it means coolant is mixing with the oil. 

3. Condition Of Engine Starting

When your car overheats and won’t start, it’s noteworthy to examine the type of problem you’re facing regarding the engine starting. There are two primary conditions of engine starting that you may encounter.

3.1. Starter motor turning the crankshaft, but the engine isn’t starting:

The first condition is when the starter motor is turning the crankshaft but the engine is not starting. This is usually accompanied by a cranking sound when you turn the ignition key. However, despite the starter motor’s turning capacity, the engine does not start. This condition could arise from several issues such as a blown head gasket, failing fuel system, ignition system, or faulty mechanical components of the engine. You should first do a compression test in that case.

3.2. Starter motor not turning the crankshaft:

The second condition of engine starting is when the starter motor is not turning the crankshaft at all. This would mean that there is no cranking sound accompanying the turn of the ignition key. Typically, this condition can be the result of either a dead battery or a faulty starter motor.

A damaged battery may prevent the starter motor from receiving enough power required to turn the engine over. On the other hand, if the battery is in good working condition, but the starter motor fails to turn, then the starter motor is probably the issue.

Common Causes Of Car Overheating

Here are some of the most common causes of engine overheating:

1. Battery Is Damaged

If the car is not even cranking after overheating, the chances are that something is wrong with the electrical system of your car, including its battery.

In the event that a vehicle’s engine overruns its preferred temperature, the consequent and unfavorable repercussions are not limited to the engine only. It is said that the battery may also encounter negative outcomes.

You may be troubled by the thought of how this could possibly occur. In that case, let us discuss this matter in greater detail.

In essence, when the heat produced by the engine rises beyond a certain level, it may cause the temperature of the battery to elevate as well.

Consequently, the fluid contained within the inner-workings of the battery may transform into a gaseous state due to such high temperatures.

This adversely affects the condition of the battery since the said fluids are responsible for ensuring that the battery efficiently stores and distributes energy.

The transformation of the fluids to a gaseous form may not only harm the battery directly, but it can also result in the formation of unwanted residual material that may accumulate within the battery and cause internal damage that distorts the overall structure of the battery.

The gradual accumulation of such damage may lead to the battery’s complete failure, resulting in the inability to retain and produce electricity.

To better illustrate this, let’s assume that you’re driving your vehicle during the summer months when temperatures are known to soar.

If for instance, you happen to notice that the car’s temperature gauge has exceeded its optimal value and continues to increase even more, it is possible that your vehicle’s battery may be affected as well.

Initially, you may find that the battery has become feeble or drained, and the vehicle is no longer able to start up smoothly.

Even if it does start up, the battery may no longer have the capability to power the electrical components of the car sufficiently. As an illustration, you may observe certain issues such as less radiant headlights or a weaker air conditioning system.

As time goes on, your car battery could catastrophically fail, such as becoming irreparably damaged. At this juncture, replacing the battery entirely becomes mandatory, which tends to be both an expensive and time-consuming task.

How to spot?

Firstly, it is important to analyze the wires that are connected to the battery terminals. If they appear melted or burned, it is likely that they have been damaged by the heat generated during the engine’s overheating.

This would mean that the battery is not receiving the required charge which will make it difficult or impossible to start the car.

The voltage of the battery needs to be checked across its terminals next. To do so, a voltmeter is required.

Attach the voltmeter’s probes to the battery posts and have someone turn on the ignition key and try to crank the car. If the recorded battery voltage when cranking is below 9.6V, it indicates that the battery is weak and requires replacement.

testing car battery

However, if the voltage of the battery is greater than 9.6V, try using a jump starter. Most cars can be jump-started even if the battery has died.

Connect the red terminals of the jumper cables to the red terminals of the battery and the black to the black terminal of the battery.

If the vehicle remains non-functional even after the jump start and the battery voltage shows close to 12V, then there must be an issue unrelated to the battery that needs further inspection.

2. Starter Motor Is Damaged

components of a starter

In the event of a car engine overheating, there is a slew of potential issues that could arise, which may include the car failing to start.

While engine overheating may not directly impact the starter motor, it has the potential to cause damage to the wiring connections that are precisely related to it.

The starter motor is responsible for the critical function of initiating a car engine. It forcefully spins the engine’s crankshaft, allowing the engine to start. The power required to execute this function is derived from the battery via the solenoid.

This impressive mechanism is set in motion when the ignition key is switched on, thus closing the circuit and prompting the motor to turn, starting the engine.

It is worth noting that the starter motor’s solenoid is composed of two distinct terminals.

One is connected to the ignition switch, while the other is connected to the battery. There also exists a wire that links the starter motor to the solenoid, which is a significant component of the starter motor mechanism.

Unfortunately, engine overheating has a damaging effect on these connections, which may cause the wiring to melt or burn. This will ultimately have an adverse effect on the starter motor’s functionality, and it may not be able to start the engine effectively.

For this reason, proper visual inspection of the wiring connections of the starter motor and solenoid is mandatory. An inspection will allow you to determine any visible signs of burning or melting, which enables you to pinpoint the location and extent of the damage.

Also Read: Where to hit starter to make it work

How to spot?

You should check the voltage between the positive terminal of the battery and the terminal on the starter solenoid which is connected to the battery. If the voltage is greater than 0.2V, it means the wire is burnt.

3. Engine Wiring Harness Is Melted/Burned

melted and burned engine wiring harness

When a car’s engine overheats, it can cause significant damage to the engine wiring harness. If you continue to drive the car after observing the temperature gauge on the dashboard pointing toward high temperature, the engine wiring harness can burn.

This happens because the wires in the harness overheat and the insulation around them can crack, causing the wires to become bare and exposed.

When the wiring is exposed, it is more vulnerable to becoming damaged or developing shorts. Additionally, exposure to high heat can cause the wiring to become brittle, making it easier to break.

How to spot?

When checking the ground wiring in an engine that has melted due to overheating, it is important to refer to the vehicle’s owner’s manual to locate the ground connections in the engine.

The negative terminal of the battery is usually connected to these ground connections, which include the engine chassis, engine block, and other mechanical components.

To ensure that the ground connections are working properly, you can use a voltmeter to measure the voltage between the negative terminal of the battery and the ground connection. If everything is fine, the voltage should be less than 0.2V.

However, if the voltage is greater than 0.2V, it indicates that there may be an issue with the ground connections.

In such cases, it is recommended to check all possible ground connections in the car and ensure that there is no breakage in the insulation of the cables.

Moreover, the contact points of the ground cables should be clean and smooth. Applying a thin film of petroleum jelly to the ground contact points can prevent corrosion and ensure a good connection.

4. Fuses and Relays Are Blown

When an engine overheats, there is a possibility that the electrical system may get damaged or short-circuited. This can cause the fuses and relays in the car to blow, which may ultimately lead to the car not starting.

To investigate this issue, you can locate the fuse box in your car. Depending on the make of your car, there may be multiple fuse boxes in various parts of the vehicle. Therefore, you should consult the owner’s manual to identify which fuse box controls which circuit.

What to do?

Once you have located the fuse box, turn the key to position two on the ignition, also known as Key On, Engine Off.

You can then use either a test light or a multimeter to check each fuse. Start by attaching the clip for the test light to any bare metal or the battery’s negative terminal, then use the probe of the test light to touch each end of a fuse.

If the test light or multimeter does not light up or show continuity, it indicates that the fuse has blown and needs replacing.

To test relays, you can watch the following video:

5. Blown Head Gasket

blown head gasket

If car cranks but won’t start after overheating, the chances are that the head gasket is blown out.

A head gasket is a thin metal gasket that sits between the engine block and the cylinder head in your car’s engine. Its primary purpose is to seal the combustion chamber and prevent oil and coolant from leaking into each other.

When a head gasket blows, it means that there is a breach in this seal, allowing oil and coolant to mix together.

how cylinder head is placed over engine block

You might be thinking about what a blown head gasket has to do with the mixing of oil and coolant. For this, you need to understand how oil and coolant flow around the engine.

Crankshaft rotates in the crankcase, where it collects the oil and sprays below the piston to lubricate it. Also, oil flows through oil galleries to lubricate camshaft and valves.

On the other hand, coolant flows through the ducts made in the cylinder head and engine block. The water pump pushes the coolant through the engine block, where it flows around the engine, and then comes out through the cylinder head.

If you closely look at the top of the cylinder block in the above picture I attached, there are holes through which coolant flows from the engine block to the cylinder head. Since a gasket sits between the engine block and cylinder head, it meters the flow of coolant properly through the cylinder head. 

When your car’s engine overheats, the metal in the engine block and cylinder head expands, putting extra pressure on the head gasket. Over time, this pressure can cause the gasket to crack or blow out completely, leading to the mixing of oil and coolant. 

If the head gasket fails, the coolant will enter the engine cylinders where it will contaminate the spark plugs, and also mix with the oil.

When oil and coolant mix together, they create a thick, sludgy substance that can clog up your engine’s components.

It can also cause decreased lubrication within the engine, leading to increased wear on engine components. This can prevent your engine from turning over, leaving you with a car that won’t start.

How to spot?

If you’re wondering whether your car’s troubles are caused by a blown head gasket, there are several symptoms to look out for. These include:

  • White smoke coming from your car’s exhaust
  • Engine misfires or a rough idle
  • Coolant leaks
  • A sweet smell coming from your car’s exhaust
  • Overheating
  • A loss of power or acceleration

Another way to detect a blown head gasket is to conduct a compression test.

Follow these steps to perform a compression test to detect loss of compression in engine:

  1. First, disconnect the electric connectors of the fuel pump, fuel injectors and ignition coils/distributor.
  2. Remove all spark plugs. Use a suitable spark plug socket to remove spark plugs.
  3. For the first cylinder, screw the compression gauge in the hole where the spark plug goes.
  4. Turn on the ignition and depress the accelerator pedal fully to keep the throttle plate open.
  5. Crank the engine up to 5 times or do it until the needle on the compression gauge is peaked and doesn’t climb anymore. If you have a push start/stop button, press brake pedal and push the button multiple times.
  6. Note down the pressure reading for each cylinder on a piece of paper. If you don’t know how cylinders are numbered in the engine, you can read this guide.
  7. If one of the pressure readings is significantly lower, it can indicate a problem with that single cylinder. 
  8. If you only have a low reading on one engine cylinder or the cylinders aren’t adjacent to each other, the issue is with the valve seal or piston ring. 
  9. If adjacent cylinders have low-pressure readings, the issue might be with the head gasket.
  10. When all your pressure ratings inside the engine cylinders are below 100 PSI for gasoline engines or below 275 for diesel, you may have a valve timing issue, or piston rings are worn-out.
  11. To determine worn-out piston rings, a wet compression test is performed. The wet compression test involves adding a small amount of oil through a spark plug hole to see if the compression reading improves, which can help determine whether the low compression is due to piston rings or valves.
  12. If the compression reading improves, it suggests that the low compression reading was due to worn-out piston rings. When oil is added to the cylinder, it acts as a lubricant and seals off the gaps between the piston rings and cylinder walls, leading to improved compression readings.

What Is The Cost Of Head Gasket Replacement?

The cost of head gasket replacement varies depending on the factors, such as the make and model of the vehicle, the extent of the damage, and the cost of labor in the area.

On average, the cost of head gasket replacement ranges from $1,000 to $2,000. However, the cost can be as low as $500 or as high as $4,000, depending on the type of vehicle and the extent of the damage. I would suggest you to also ask a mechanic for an expert advice.

6. Fouled Spark Plugs

fouled spark plugs

When a car engine overheats, it can lead to the blowing out of the head gasket. A blown head gasket can lead to the mixing of the engine’s coolant and oil, which can then enter the engine cylinder.

If this happens, it can cause the spark plugs to get fouled. Fouled spark plugs cannot generate the spark needed for combustion, which can cause the car not to start.

If your car experiences this issue, it is important to replace the fouled spark plugs as soon as possible.

However, it is essential to avoid choosing cheap aftermarket parts as they can easily become defective and cause starting issues. The best option is to purchase spark plugs that are recommended by the original equipment manufacturer (OEM).

How to spot?

Remove the spark plugs using spark plug socket, crank the engine. and see if water or oil squirts out of the spark plug hole.

7. Failure Of Transmission

When a car overheats, it can cause significant damage to many of its components, including the automatic transmission. The reason behind this is that automatic transmissions run on transmission fluid. This fluid is responsible for lubricating and cooling the transmission system. 

If the car overheats, it raises the temperature of the transmission fluid. If the transmission fluid becomes too hot, it can start to break down, causing various problems.

The radiator typically has an extended part, called transmission cooler, which helps transfer heat from the transmission fluid into the coolant, and maintain the proper temperature. However, if the car overheats, the transmission cooler may not be able to do its job adequately.

The hot transmission fluid can cause the formation of varnish at around 240 degrees, which can impede the flow of fluid and cause the transmission system to overheat even further. This can cause seals to harden, plates to slip, and eventually cause the seals and clutches to burn out.

The heat also creates carbon deposits which can clog up the transmission’s internal mechanisms and cause them to fail.

8. Warped/Melted Timing Belt

In an engine, the timing belt or chain is responsible for synchronizing the movement of different engine components such as the crankshaft and camshaft. The belt or chain ensures that the valves open and close at the right time, preventing any damage between the pistons and valves.

A timing belt is made of rubber and is responsible for transmitting the rotational movement of the crankshaft to the camshaft(s). 

In terms of the overheating of an engine, it can cause damage to the timing belt material, warping or even melting it entirely. If this happens, the belt may jump a tooth on the camshaft and cause poor valve timing, making your engine stalling, rough idling or not starting.

When it comes to removing the timing cover, it is indeed an expensive job. Although, in certain situations, it may be necessary to remove the timing cover to check for any timing belt/chain issues. However, this should always be a last resort, if other simpler and cheaper procedures.

9. Warped Cylinder Head

When the engine overheats, the metal components of the engine, such as the cylinder head, can expand beyond their normal thermal expansion limits.

If this overheating is severe enough, it can cause the cylinder head to warp, which means that it is no longer perfectly flat. This warping can lead to a loss of compression even if the head gasket is fine.

The head gasket sits between the engine block and the cylinder head, and its job is to seal the combustion chamber, which is where the air and fuel are ignited to power the engine.

If the cylinder head is warped, the head gasket may no longer be able to provide a good seal for the combustion chamber.

This can lead to a loss of compression, which means that less air and fuel are getting into the cylinder, resulting in a weaker combustion process that will cause the car not to start.

How to spot?

Inspecting a cylinder head is an essential step in engine rebuilding or repair process as a warped cylinder head can cause significant engine problems. Here is how to inspect a warped cylinder head:

First, ensure that the cylinder head is clean and free from any debris. Then place the straight edge across the cylinder head, using a feeler gauge to check for any gaps between the surface of the cylinder head and the straight edge. If there is a gap, it indicates that the cylinder head or block is warped, and repairs are needed to correct this issue.

Causes of Car Overheating

Here are the following causes due to which your car may overheat:

1. Low Coolant Level

The engine of your car produces a lot of heat when it is running. Coolant circulates through the engine to absorb this heat and carry it to the radiator, where it is dissipated into the air.

When the coolant level in your car’s engine is low, it cannot absorb and carry away the heat generated by the engine effectively. This results in the engine overheating and potentially causing serious damage to its components

There are several reasons why coolant level can be low, including:

  1. Leaks: Coolant can leak from hoses, gaskets, and other engine parts. You can check for leaks by looking for puddles of coolant under your car or by smelling a sweet odor coming from the engine.
  2. Evaporation: Over time, coolant can evaporate from the engine, especially if it is not properly sealed or coolant reservoir cap is missing.
  3. Flushing: If your car’s cooling system has not been flushed in a long time, sediment and rust can accumulate and displace the coolant, causing a low level.

2. Stuck Thermostat

schematic of engine thermostat

A thermostat is a small device that regulates the temperature of your car’s engine. It is located between the engine and the radiator and controls the flow of coolant, which helps to keep the engine at a safe and optimal temperature.

When the engine is cold, the thermostat remains closed, preventing the coolant from flowing into the radiator. As the engine heats up, the thermostat opens, allowing the coolant to circulate and cool down the engine. 

When a thermostat gets stuck in the closed position, it prevents coolant from circulating through the radiator. As a result, the engine starts to heat up rapidly, and the temperature gauge on your dashboard begins to rise. 

To locate the thermostat, you just need to follow the upper hose of the radiator as its one end is connected to the thermostat. A thermostat is located closer to the water pump.

3. Clogged Radiator

clogged radiator causes overheating

Your car’s radiator works by circulating coolant through a series of small tubes. As the coolant flows through these tubes, it absorbs the heat generated by your engine.

The heated coolant is then circulated back to the radiator, where it passes through a series of fins.

These fins increase the surface area of the radiator, which allows the heat to dissipate more efficiently. As the coolant passes through the fins, it releases the heat it has absorbed, which allows it to cool down. 

Over time, a radiator can become clogged due to the accumulation of dirt, debris, and other contaminants.

This buildup can obstruct the flow of coolant through the radiator, causing it to overheat. When a radiator is clogged, it cannot effectively cool the coolant, which in turn causes the engine to overheat. 

One way to check if a radiator is clogged is to use an infrared thermometer and check the temperature at multiple locations. If the temperature is not consistent, it could indicate a clog.

Preventing a clogged radiator is relatively simple. Regular maintenance and cleaning of the radiator can help ensure that it remains free of dirt and debris.

You can clean your radiator by using a hose to flush out any buildup of dirt and debris. Additionally, you should ensure that your car’s coolant is changed regularly, as old coolant can become acidic and cause buildup in the radiator.

To flush the cooling system, perform these steps:

  1. Drain the radiator by removing the valve in the bottom of the radiator.
  2. Plug the radiator valve and fill the radiator with distilled water.
  3. Start the engine and drive for around 20 minutes. Make sure that you run the heater on high mode.
  4. Flush the water from the cooling system.
  5. Add the recommended coolant/antifreeze into the engine with a 50/50 ratio.

4. Malfunctioning Radiator Fan

If the radiator fan malfunctions, it can cause a number of problems for your car. The most obvious issue is that the engine will start to overheat. This is because without the fan drawing air through the radiator, the engine is not receiving the necessary cooling it needs to stay at a safe temperature.

Radiator fan is electrical and is controlled by the ECU. If the radiator fan is not working, you should also check its harness connector.

Car Won’t Start After Overheating: FAQs

What causes a car to overheat?

Common causes of a car overheating include a malfunctioning thermostat, low coolant levels, a leak in the cooling system, or a failing water pump.

How do I know if my car has overheated?

Signs of an overheating car include a rising temperature gauge, steam coming from the hood, or a burning smell.

What should I do if my car overheats?

If your car starts to overheat, pull over to a safe location, turn off the engine, and let it cool down. Check the coolant level and look for any leaks in the system before attempting to start the car again.

Why won’t my car start after it overheated?

Overheating can cause damage to the engine and its components, such as the head gasket or cylinder head, which can lead to a loss of compression and prevent the car from starting. 

How can I prevent my car from overheating?

Regular maintenance, such as checking coolant levels and replacing worn belt or water pump or radiator hoses, can help prevent overheating. Additionally, avoiding driving in extreme heat or stop-and-go traffic can reduce the risk of overheating.

Can overheating cause permanent damage to my car’s engine?

Yes, overheating can cause irreversible damage to the engine, such as warped cylinder heads, damaged pistons, and cracked engine blocks. 

Is it safe to add coolant to an overheating engine?

It is important to let the engine cool down before opening the radiator cap to add more coolant. Otherwise, the hot coolant can cause burns. 

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