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What to Do When a Car Overheats and Won’t Start

Car engine overheating with hot steam coming out of the radiator

Car troubles can be very frustrating and confusing. After your car overheats, there can be hidden damages that prevent you from getting your car started again. Too much heat under the hood can cause a whole slew of problems.

If your car won’t start after overheating, you’ll need to pop the hood and look at some of the parts. Start by checking your oil, coolant, and air filter. These are parts that need to be routinely replaced and the repair is very simple. From there, look for blown gaskets, cracked heads, trouble in the fuel system, and problems with your starter motor. These repairs require more effort and they’re less likely, but they’ll definitely stop your car from starting after overheating.

In this guide, I’ll be addressing cars that overheat and then don’t start afterward. I’ll start by explaining the overheating process, go through some signs of overheating, help you through the troubleshooting stage, and give you tips for driving a car that’s overheating.

Why Cars Overheat

Before getting into troubleshooting, I want to talk about the basics. In this section, I’ll review why your car overheats and what stops it in the first place.

In the world of physics, heat is generated when two things are moving, there’s some chemical reaction, or any amount of friction exists.

When you pop your hood, you might not always be able to see the problem right away but under the surface and when the engine is running, there is fuel exploding in your engine block, pistons are shooting around, and plenty of parts are rubbing together.

Illustration diagram of an internal combustion engine showing how the fuel combustion works with spark and air

If you just let this process happen without any safeguards, you’ll be able to drive your car a few feet before it’s too hot to operate.

To reduce friction and minimize the heat generated from motion, there’s oil and grease. That’s the key reason why you change your oil routinely. Oil has very low friction and it lubricates items for a long time. Now, the friction and motion will make less heat.

What about the explosions happening in your engine block? Unless you swap to a Tesla, there’s no way to avoid this. Instead, your car adopts a second system that gets rid of the generated heat and keeps things cool.

If your car is too hot, parts will melt, components will physically change shape, and the fuel won’t be reliably consumed. Once it’s hot enough, things start to crack and fall apart, and your engine will “seize”, meaning it won’t move your car anymore.

Engine Cooling System Illustration

This is why your car has a “coolant system”. To dramatically oversimplify things, your coolant system takes heat away from the engine and pumps a cool liquid across hot parts. This process draws heat away from heat-sensitive parts and keeps everything cooler.

The system itself uses a pump to move around the coolant, plenty of hoses, a radiator, a fan, and a thermostat that turns the process on and off.

As this guide continues, you’ll learn more about each of these components (spoiler alert, you’re probably overheating because one of these parts isn’t working correctly).

How to Know if Your Car Is Overheating

The next step is to figure out if you’re actually overheating. The good news is that it’s very easy to spot a car that’s overheating.

Hot cars generate a lot of steam. Steam is a grayer, lighter color as opposed to black plumes of smoke.

Another hint is that your engine temperature gauge is in the red area with the “H”. Of course, this part of the gauge refers to an engine that’s too hot.

If your overheating is due to a leak, you’ll also notice a unique smell when you pop the hood. It might be sweet or smell like something’s burning.

Close up of a BMW car temperature gauge showing hot engine overheating

Diagnosing Why Your Overheating Car Won’t Start

With that insight, now we can learn about the diagnostic process. It’s a little trickier than other problems you might encounter around your car. For one, your car isn’t turning on so the indicators, sensors, and gauges aren’t doing anything. In addition, a lot of the coolant system is hidden behind other parts and they might be tough to visually inspect.

With that said, here are a few troubleshooting steps to try out.

Check for a Loose Battery

I would suggest starting with the battery when you open the hood. It’s an easy place to start and will save you a lot of time if it’s the culprit.

The battery terminals should be firmly attached to the battery, the case should be fully seated, and it shouldn’t be bulging or leaking.

A rogue battery can cause a ton of extra heat. Since it’s so close to your engine block and there’s nothing cooling down the battery, it will quickly transfer heat around your engine bay.

Man unscrews or screw on tightening the positive terminal post of the car battery with a wrench and gloves on

Examine the Air Filter

Coming air is a big driving force behind keeping your car cool. To keep dangerous airborne particles away from sensitive engine components, a filter is used. All incoming air will pass through a filter that has tiny holes in it. The holes are small enough for air to go through, but too small for debris, rocks, and dirt to get into your engine.

The problem is that these filters clog over time. If your air filter doesn’t have enough free space for air to flow, then the whole system will choke and not cool your engine enough.

Is Your Oil Okay?

I mentioned earlier that oil is the engine lubricant that keeps moving parts lubricated and cool. Over time, the oil will absorb particles and become less efficient at doing its job. This is why it’s ideal to change it at the recommended intervals for your vehicle and not wait too long.

If you go too long between oil changes, then you won’t have enough “good” oil to cool down your engine. Alternatively, you might have an oil leak. If there isn’t enough oil in the system, you’ll also experience overheating.

Auto mechanic draining the car engine motor oil from the oil pan under the car

A Blown Gasket

Gaskets are used all over your car to keep components sealed. Sealing them makes sure liquid is contained and there’s no cross-contamination.

When a gasket gets cracked, broken, or torn off, then the seal is broken and liquid can escape. For instance, a gasket used to keep your oil contained might blow, allowing oil to spill out and making your car overheat.

Finding a blown gasket is a matter of looking at the rubber used under your hood and ensuring there is no liquid oozing out of the seams.

A Melted, Warped, or Cracked Head

When your engine gets seriously hot, then the head can become damaged. This is perhaps the most expensive mistake to make when your car overheats.

The cylinder head is above all of the cylinders and it contains the explosions and motion within the engine. If there’s any damage at all to your cylinder head, things can get unpredictable and your car might not start up again.

Old car engine taken out of the car showing the valves and engine block needing repair

Troubleshoot the Fuel System

If too much fuel is going into your engine, then the mixture will be off. With a fuel-rich mixture, too much heat is generated without enough energy getting created. The result? An engine that runs hotter than it should.

With a steady flow of too much fuel, your engine will quickly overheat and cause some other problems on this list.

Another issue is that this mixture can create too much vapor. This restricts the airflow within the engine and expedites the overheating process.

This problem can be caused by almost any component in your fuel system: the fuel pressure regulator, fuel pressure damper, fuel lines, or even the fuel injector.

Do You Have Enough Coolant?

Another big question is how much coolant you have. Since coolant is circulated in a closed-loop system, it means that your car can only use as much coolant as it has in the reservoir.

If there’s not enough, then you don’t have enough liquid to get rid of engine heat and transfer the energy away from heat-sensitive components.

You might run out of coolant from a leak or just naturally over time. If you haven’t topped off your coolant reservoir in a while, I would suggest starting there. The reservoir is towards the back corner of your engine bay, and there’s an indicator that shows you how much fluid should be in there.

Pouring anti-freeze engine coolant into the reservoir

Car Starter Failure

If you overheated while driving, then that heat might have made its way to the starter motor. For reference, the starter motor does the initial startup which ultimately powers your engine. Turning over an engine alone takes a ton of power and it’s difficult to do.

Instead, turning your key will start a tiny starter motor that turns a crankshaft and brings your engine to life.

If the motor itself, any of the wiring, or the solenoids overheat, then they could melt or separate. This results in a starter motor assembly that doesn’t work. You can turn your key all you want, but the friend starter won’t get your engine going.

Since this is a largely electric assembly, it’s very sensitive to heat. It doesn’t take much to overheat it and kill the starter motor.

Old and dirty car engine dynamo starter motor lying on the asphalt

Is Your Engine Grounded?

If things got too hot under the hood, it’s possible that the engine’s ground wire got split or damaged. The ground is required for the engine to operate safely.

Without proper ground, your lights might flicker, the battery could die, or you could have trouble starting your car.

Your Engine Is Vapor Locked

Another issue with too much heat is called “vapor locking”. This is when the fuel in your line heats up so much that it vaporizes.

Your fuel lines are designed to only have liquid fuel in them. If vapors are trapped in the line, the flow of fuel will be interrupted and inconsistent.

As a result, the flow of fuel while you’re starting your car might not be enough. The trapped gas vapor will not allow enough liquid fuel to go to your engine. Without the right amount of fuel, your engine won’t start, meaning your car won’t start when you turn the key.

Black fuel lines visible with the car mounted on a hydraulic lift with a view of the underbody at a car service workshop

What to Do When a Car Overheats

It’s also worth discussing what you should do when you first notice your car overheating. This will happen while the car is on and you’re driving since idling rarely creates enough heat to overheat your engine.

Pull Over and Stop the Car

Before doing anything else, you need to pull over and turn off your car. If your car is overheating and you keep driving, you risk doing massive damage to your engine block and head gasket. They can crack and seize, potentially totaling your car and leading to a repair bill of thousands of dollars.

By pulling over and turning off your car, you’re preventing further damage. It’s not worth the risk to keep driving until you find the next mechanic, just pull over at the first safe area.

Pop the Hood

Now it’s time to open the hood. This will achieve a few things — first off, it will help the engine cool down. Opening the hood allows for a lot more airflow to go through the engine bay. It also allows you to start troubleshooting.

When your car is overheating, you need to be very careful when your hood is popped. Parts under the hood could be hot enough to burn your skin if you touch the part. You want to make sure you never touch any hot parts of the engine.

Driver on the road having a problem with the car overheating with smoke visible after opening up the hood

Check the Coolant

Whenever I have a car that’s overheating, I always start with the coolant. By definition, this fluid is supposed to keep your engine cool. Since the engine isn’t cool, there’s a chance that you don’t have enough coolant in the system.

You can do this on the side of the road because checking and refilling your coolant only takes a minute. The coolant reservoir is going to be in the back corner of your engine bay.

The cap of your coolant will be metal, and the reservoir will be plastic. These are two separate places where you can add coolant, but I would suggest adding it to the reservoir.

For one, the reservoir is going to be cooler and not as pressurized. Opening the inline cap can cause the cap to go flying, it can burn your hand, and it can let out hot vapors that can burn you as well.

The other reason I suggest working from the reservoir is that there will be an indicator on the tank that tells you how much coolant you should have. If your fluid is below that line, then there’s a clear sign that you need to add more coolant.

If you don’t have coolant in your trunk, then you’ll need to pick some up. Your car is out of commission, so you’ll have to call a friend or get a ride to a local auto shop or superstore like Walmart.

It’s possible to use a water bottle in the coolant reservoir to top things off and hopefully cool your car down enough to drive to a store if you’re in the middle of nowhere. In my experience, it doesn’t always work. I’ve had times that topping off with water only got me another 5 minutes on the road before I needed to pull over again.

Mechanic pouring car engine anti-freeze G12 coolant into the coolant reservoir tank

Get a Tow and Start Troubleshooting

If coolant isn’t your issue, then you’ll, unfortunately, have to get a tow somewhere so you can start troubleshooting.

For this, you have two options: you can have your car towed to your house or to a local mechanic. If you go to the mechanic, they’ll take care of the problem for you. If the mechanic is honest, they’ll do the troubleshooting and tell you what the culprit is before doing any repairs.

If you take the car home, you’ll want to go through my troubleshooting section earlier in this guide. After you successfully diagnose the problem, you’ll need to repair or replace the part to ensure your car works again.

Even after getting your car to start, you should be skeptical. Drive around the block a few times and see if the temperature gauge spikes again. It’s more common than you might think. Personally, every time I fix an overheating car, I find another reason why it’s overheating within the next few days.

Close up of an auto mechanic at work on a car with the hood open inside his garage

Conclusion

At this point, you should have a better understanding of why your car overheating, some potential culprits, and what to do from here. I hope that this guide helped you and remember that you should pull over and turn off your car as soon as it overheats to avoid further damage.

For more DIY repair guides and troubleshooting help, explore the rest of my blog. I also have a list of products that might help you in the future. Leave a comment below if this guide helped you, and feel free to share this article with friends.

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References:

Motor Hills

Bryan’s Garage

Car Overheated Now Won’t Start – Reasons And Solutions

Firestone

What To Do & Not Do When Your Car Overheats

Get Jerry

Why Won’t My Car Start After Overheating?

Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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