What Happens If You Drive with Low Coolant?

Gasoline engines, diesel engines, hybrid vehicles, and even electric cars naturally create heat. When you use your car’s heater, some of this heat is channeled into the cabin for your comfort. A majority of the heat, however, must be managed another way.

To ensure the engine stays at an optimal operating temperature, your car relies on a fluid called antifreeze, or engine coolant.

Coolant/antifreeze is the most important fluid under the bonnet, maintaining the temperature of the engine to prevent overheating. But what happens to a car when there’s no coolant in the system?

In this guide, we’ll look at:

  • What happens to an engine with no coolant?
  • Effects Of Low Coolant in Car
  • How modern engines deal with low coolant and overheating
  • Causes Of Coolant Loss

What Happens to An Engine with No Coolant?

Coolant/antifreeze circulates through the engine, maintaining the correct working temperature of different components. If your car runs out of coolant on the road, you’ll likely experience the following:

What Happens If You Drive with Low Coolant

1. Dashboard warning light or abnormal temperature gauge – The first sign of low coolant should be a dashboard warning light or a rising temperature gauge.

2. Automatic engine cut-off – If you drive a modern car, it will be fitted with an automatic engine cut-off feature. This is designed to prevent damage when the engine starts to heat up due to a lack of coolant. You won’t be able to drive the car further until it’s cooled down.

3. Damage to engine parts – If your car doesn’t have a cut-off feature and you continue driving, you’ll risk damaging parts of the engine that are running too hot. This may not only lead to pricey repair bills but could result in permanent and irreparable damage.

The parts of your car that can be affected by overheating failure include:

  • Water pump
  • Head gasket
  • Cylinder and piston timing
  • Cylinder head
  • Warped or bent connector rods
  • Crank failure

4. Other symptoms of low or no coolant – Aside from the mechanical engine issues caused by low to no coolant, you could notice other problems such as billowing steam, a dangerously hot bonnet, and no control over the interior heating system. if you notice any of these, pull over to try and prevent even more damage.

Effects Of Low Coolant in Car

Before your car’s engine starts taking heat damage or cuts out, there are several warning signs that can alert you to a cooling system fault. It’s important to be able to recognize these signs as, depending on the age and condition of your car, the engine may sustain damage before the dashboard warning light comes on.

Common warning signs to look out for include:

Your Engine Could Overheat.

Coolant helps pull heat away from the engine. So, without enough coolant, the engine could overheat or seize up. Continued use of an overheated engine could lead to permanent damage, such as pistons welding to the cylinders.

You Could Blow a Head Gasket.

If you’ve ever said, “I am about to blow a gasket,” to describe your mood you know that this happening to your engine is bad news! Low coolant can sometimes cause a head gasket on your engine block to blow.

If this happens, you may notice smoke emitting from the engine or tailpipe, a loss of power, engine knocking sounds, or decreased efficiency.

Your Car Could Shut Off.

Some cars have a safety system in place to automatically shut the engine off before it suffers significant damage which can happen due to low coolant.

While this may help save you from extensive repairs stemming from an overheated engine, it can be very dangerous depending on where you are driving when the engine shuts off.

Low Coolant Symptoms

Low coolant symptoms can vary depending on how low your vehicle is on antifreeze. Typically, low coolant will trigger your antifreeze light. Some vehicles might display a “Check Coolant” message on the dashboard. If your coolant light is on, you may notice some of these oddities.

The High-Temperature Gauge Is Near or In the Red.

One tell-tale sign of low coolant is the high-temperature gauge on the dashboard. This gauge is designed to tell you when the engine is getting too hot.

Most often, the gauge should stay near the center of the H and C symbols. If the gauge is reading close to the H, shut your engine down and have it towed to repairs.

The Ac System Is Malfunctioning.

When you use your vehicle’s heat, the coolant helps regulate the flow of hot air into the cabin. If the coolant is low and your air conditioning is running, you may notice hot air coming from your car AC vents.  (In winter, try these tips to stay warm when your heat isn’t working!)

There’s A Sweet-Smelling Odor.

When there’s a coolant leak in your vehicle, you may notice a sweet smell in your air conditioning or under the hood. This is because antifreeze contains glycol, a sweet, viscous liquid used to help regulate the freezing and boiling point of water.

While strange odors may be a sign of car issues, they are not always a clear indicator. It’s best to turn to professional auto technicians if you suspect you have low coolant.

Your Coolant Level Sensor Is Faulty.

Sometimes, an illuminated coolant light may be due to a faulty coolant level sensor. If this sensor malfunctions, it could be causing the coolant light to turn on even if you don’t have low antifreeze levels.

How Modern Engines Deal with Low Coolant and Overheating?

Running out of coolant/antifreeze won’t necessarily cause instant damage though, depending on your car. In modern, high-end cars, the engine control unit (ECU) often features a safe/limp-home mode, which reduces the risk of damage by firing cylinders in a different sequence.

This means that cool air from the inlet is fed into one bank of cylinders at a time, allowing the other rack to cool slightly between firing. This gives the option of driving further even when the engine is overheating, which could be enough to get home or to a garage.

As well as this, many new cars feature automatic cut-off, which is designed to protect the engine from heat damage. This uses the cooling system’s thermostat to kill power to the engine when the temperature reaches a certain point and means that the car can’t be restarted until it has cooled down sufficiently.

Causes Of Coolant Loss

Unlike engine oil, which can be changed as frequently as 3,000-5,000 miles, you normally don’t have to check and replace coolant as often.

In fact, since coolant works within a closed system, it shouldn’t become low unless there’s a leak, in which case you should visit your local car care experts for radiator services and repairs. There are a few common ways in which coolant fluid can leak:

  • External leaks from radiator hoses, connections between hoses, or from the radiator itself
  • Radiator cap leaks due to a faulty seal on the cap where the pressurized coolant can leak out
  • Internal leaks where coolant may leak out of places such as the engine’s head gasket