Car Overheated Now Won’t Start (Why & What Should You Do)

It can be extremely stressful dealing with a car that has recently overheated and is no longer starting. Overheating is one of the most serious issues that car owners face, and knowing how to handle it and avoid it can help mitigate the stress of dealing with the problem.

A car that has overheated and won’t start is typically caused by a damaged thermostat, low coolant, or a damaged battery. Other causes include a blown head gasket, a warped cylinder head, or faulty electrical components like sensors or engine grounds. In some extreme circumstances, an overheating vehicle can be caused by a seized engine, which is a serious problem that could lead to expensive repairs.

This guide will provide you with all of the information that you need to determine the cause of your overheating issue and how to resolve them. There will also be preventative measures detailed to avoid overheating in the first place.

10 Reasons Your Car Won’t Start After Overheating

Damaged Thermostat

A damaged thermostat is a common cause of vehicle overheating and not starting again. The dashboard of your vehicle has an internal dial that keeps up with the temperature of the entire system. If this thermostat is not working properly, the system’s temperature will not be relayed properly to the ECU.

Incorrect thermostat readings will affect other internal components of your vehicle and eventually cause overheating. You will need to have your vehicle serviced and the thermostat replaced if you notice the engine running hotter than usual.

If you do not address damaged thermostat issues in a timely manner, you run the risk of severely damaging the engine of your vehicle. This could lead to costly repairs so it is best to get it taken care of as soon as possible.

Low Coolant

Low coolant is a common cause of vehicles overheating and not starting again properly. Coolant, in either gas or liquid form, is used to manage the internal temperature of the motor system. When the coolant levels are too low, then you will not be able to start your car properly.

Keeping an eye on the coolant levels can help you avoid overheating. If you notice that your vehicle is low on coolant, it is not advised that you drive it until you are able to fill the coolant levels up to the appropriate levels. Driving with low coolant can cause serious issues for your engine.

Warped Cylinder Head

A warped cylinder head can also cause your car to overheat and not start up properly. A warped cylinder head and a blown head gasket typically occur at the same time, so both issues will need to be addressed before your vehicle will drive again.

If your car turns over but doesn’t start after overheating, it is likely that the cylinder head has warped due to a blown head gasket. The cylinder head inside of your vehicle should always be straight and uniform.

A car that has overheated can cause the cylinder head to expand past what is normal, causing damage to other components of your engine block. Luckily, a warped cylinder head can generally be repaired and flattened, and shaped back to normal size.

Depending on the severity of the warping, you may find that you need to have your cylinder head replaced completely. In most cases, it is more sensible to replace a warped cylinder head if you are able rather than have it formed back to its normal size.

Blown Head Gasket

A blown head gasket is a common cause of vehicles overheating and not starting up again properly. A blown head gasket is the result of intense heat causing the cylinder head and engine block to expand beyond their normal size.

This expansion will cause coolant to leak into the combustion room and blow the head gasket. In most cases, when the head gasket is blown out, the cylinder head will warp along with it. This means that both these components of your vehicle will need to be replaced before it can be restored to safe driving condition.

A blown head gasket will cause your engine to lose power and eventually not start at all until the issue is resolved. There is also the possibility of significant coolant loss that will be undetectable by a pressure test. This could result in further engine damage due to a lack of proper coolant levels.

You can typically identify a blown gasket if you are seeing visible white smoke coming out of the exhaust or bubble formations in the radiator. You will need to take your vehicle to a mechanic and have your head gasket replaced if it has blown.

As previously mentioned, it is likely that the cylinder head will also need to be replaced if the head gasket has blown. Both of these components are extremely complex to repair or replace so a mechanic will likely be necessary.

Damaged Battery

A damaged battery can also cause your vehicle to overheat and not start. Once your vehicle begins to overheat, the likelihood of your battery becoming corroded or damaged increases significantly. Your car’s battery is responsible for powering the ECU and other vital electrical components of your vehicle.

If the battery is damaged and no longer holds a charge properly, it will begin to affect your car’s signal transmission and functionality and the battery could die while driving. You will need to inspect the battery and recharge it or replace it. It is not advised that you drive while your battery is damaged to avoid your car shutting down while you are currently driving. This will cause unsafe driving conditions for you and other drivers.

Faulty Sensors

Faulty sensors are another common cause of overheating. The sensors in your vehicle are responsible for controlling the system’s components that delegate power return to your car. If the sensors are not relaying accurate information, it will begin to affect the functionality of these components.

A quick inspection of the ECU and fuses will allow you to determine if the sensors are damaged. Any damaged sensors that you find should be replaced as soon as possible. An OBD code scanner tool can also be used to find any sensor faults in your car’s system.

Engine Ground Connection Problem

A bad engine ground connection can also cause your vehicle to overheat and not start properly. Circuit resistance from the faulty engine ground will eventually begin to affect the whole electrical system of your vehicle.

This could cause the whole electrical system of your vehicle to shut down while driving and put you and other drivers in a very dangerous situation. Checking the engine ground for connection problems will help you resolve these issues and avoid further damage to the engine.

Most engine ground connection problems occur after recently changing the battery of your vehicle. Because of this, checking the battery connection as well as the engine ground may be necessary to get your vehicle to start again.

Starter Motor Damaged

A damaged starter motor is another common cause of overheating. The starter motor is responsible for transferring the electricity to the starter control unit from the battery. This process will power the starter solenoid that allows your key to start your engine.

If the starter motor is damaged, it will not be able to mitigate the power properly, causing the temperature to grow hotter, leading to overheating. When this happens, your vehicle will not start properly due to being overheated.

You will need to replace the starter motor before you will be able to start your vehicle properly. It is advised to take your vehicle to a mechanic and have them replace the starter motor.

Seized Engine (Worst Case Scenario)

A seized engine is one of the most serious issues that your vehicle can have. Once your vehicle has overheated and won’t start properly, it could mean that your engine has seized. To know for sure, you will need to use a ratchet to turn the crankshaft clockwise.

If the crankshaft will not turn properly, you are most likely dealing with a seized engine. Unfortunately, a seized engine cannot be repaired and will need to be completely rebuilt or replaced before your vehicle will work again.

This could potentially cost you thousands of dollars and is one of the worst-case scenarios for your vehicle. In most cases, depending on how new your vehicle is, it is more practical to replace your vehicle rather than the engine.

If you wish to keep your vehicle, you can consider replacing the engine with a used one to save money. It is best to avoid overheating to lower the likelihood of a seized engine. Ways to prevent your vehicle from overheating have been detailed in the section below.

Ways To Prevent Your Car From Overheating In The First Place

Some of the ways that you can prevent your vehicle from overheating include maintaining proper coolant levels, avoiding the AC in your vehicle, and keeping a close watch on the temperature gauge. Maintaining the proper coolant levels will ensure that your vehicle can cool itself properly and avoid overheating in the future.

Avoiding the AC can relieve your vehicle from extra internal heating which is the byproduct of using the AC in hot temperatures. You should always keep an eye on the temperature gauge to ensure that your vehicle is operating within the optimal temperature range.

Keeping your vehicle parked in the shade can also help avoid excess heat from direct exposure to the sun. Leaving the windows open on extremely hot days can also help to mitigate the internal temperature of your vehicle.

All of these preventative measures should be used in tandem with regular maintenance. This will lower the likelihood of encountering any of the serious issues caused by an overheating vehicle. If your vehicle has recently overheated, you will need to open the hood and let it cool down for at least 30 minutes.

This will give the engine enough time to cool of and allow you to inspect it or attempt to drive it to be serviced.


An overheating car that won’t start anymore can be caused by several issues including blown head gaskets and warped cylinder heads, faulty electrical components, or a damaged battery. The most severe cause of overheating includes a seized engine.

All of these issues can cause permanent damage to your vehicle if you do not address them as soon as possible. It is not advised that your drive your vehicle if it has recently overheated until you determine the cause and address the problem.

If your vehicle has recently overheated, it can be up to thirty minutes before it cools down enough to inspect or drive again. Opening the hood and allowing the engine to cool down will help this process go faster.