Vapor lock

Vapor Lock: What is it, why does it happen, and how do you fix it

Modern fuel-injected engines have eliminated the issue of vapor lock, which was common in cars with carburetors. It is important to understand what vapor lock is and why it used to be a concern for drivers. If you still drive a carbureted vehicle, you should prevent vapor lock. It can create a variety of issues, including difficulties starting and driving the car.Vapor lock

Well, in this article, we’ll be understanding the vapor lock better, as the answers to the following questions will be discussed:

  • What is a vapor lock?
  • Why does it happen?
  • What are the symptoms of vapor lock?
  • How to fix the vapor lock?
  • How to prevent vapor lock?

Ok, let’s get started!


What is a vapor lock?

Vapor lock is an issue produced by liquid fuel converting to gas while still in the fuel delivery system of gasoline-powered internal combustion engines. This interrupts the operation of the fuel pump, resulting in a loss of feed pressure to the carburetor or fuel injection system, resulting in momentary loss of power or full stalling. Starting the engine in this situation may be difficult.

The fuel may evaporate due to engine heat, the local environment, or a lower boiling point at high altitude. In areas where lower viscosity (and lower boiling threshold) fuels are utilized during the winter to ease engine starts, prolonged usage of specialty fuels during the summer might cause vapor lock to occur more easily.

Why does it happen?

Vapor lock occurs when the fuel in your car becomes too hot and vaporizes. If the outside temperature is high enough, or if the engine is running at higher temperatures, and the fuel lines are too close to the exhaust, vapor lock can occur. It can also happen if you drive at higher elevations or use a winter fuel blend in your vehicle once the weather warms up.

What are the symptoms of vapor lock?

The following are the most common symptom of vapor lock:

  • Misfires
  • The Engine Is Difficult to Start
  • Performance Issues


After the engine has started, it still needs the proper air-to-fuel ratio to function properly. Vapor lock disrupts this supply, causing the engine to run lean. Because of the partial combustion that occurs when an engine runs lean, it is prone to misfiring. The engine will not only run rough, but it may stall if the vapor lock is especially bad.

The Engine Is Difficult to Start

The engine requires numerous things to function properly, one of which is fuel. To function properly, the engine requires a precisely regulated air-to-fuel ratio. This combination works with compression and ignition to start the engine. A vapor lock in the car will disrupt fuel delivery. The engine may be difficult to start if there is insufficient fuel. When you try to start the vehicle after it has warmed up, you may have extra problems.

Performance Issues

When the engine does not receive enough gasoline, it is said to be starved. Just as we cannot function without food (fuel), the car cannot function without its power source. Even if you press hard on the gas pedal, the vapor lock causes poor acceleration and hesitation. You may also notice a decrease in fuel efficiency as a result of the malfunctioning operation.

How to fix the vapor lock?

Vapor lock is a problem that can occur in internal combustion engines, particularly in older vehicles with carburetors or low-pressure fuel systems. It happens when the fuel in the lines and carburetor turns into vapor due to excessive heat, causing the engine to stall or run poorly. If you suspect vapor lock is the issue, here are some steps to help you fix it:

Identify the problem:

Check to see if the symptoms you’re experiencing are truly due to vapor lock. When the engine gets hot, it may stall or lose power, but it will resume normal operation once it cools down.

Allow the engine to cool:

If you have a vapor lock while driving, pull over and let the engine cool. This can aid in the re-conversion of vaporized gasoline to liquid and the restoration of appropriate fuel flow.

Check the fuel system:

Examine the fuel lines, particularly those near heated engine components. Examine the fuel system for any damaged or kinked lines that may be leading to excessive heat.

Ensure proper fuel pressure:

Low fuel pressure might contribute to vapor lock. Use a fuel pressure gauge to check the fuel pressure, and if it’s low, reference your vehicle’s manual for the proper pressure parameters. If the pressure is incorrect, you may need to replace the gasoline pump or pressure regulator.

Insulate the fuel lines:

If the fuel lines are too close to heated engine components, protect them with heat-resistant insulating materials such as heat sleeves or wraps.

Improve engine cooling:

Check that your engine’s cooling system is functioning properly. Check the coolant, radiator, and cooling fan levels. A properly operating cooling system will assist control engine temperatures, lowering the likelihood of vapor lock.

Use high-quality fuel:

Low-quality or low-octane fuel might boil faster, increasing the possibility of vapor lock. Always use the correct fuel type for your vehicle, and try using higher-octane fuel if the vapor lock persists.

Upgrade the fuel system:

Consider updating to a modern fuel injection system if you have an older car or one that is prone to vapor lock. Because they work at higher pressures and atomize the fuel more effectively, fuel injection systems are less prone to vapor lock.

Park in the shade:

When parking your car, try to find a shady place or use a sunshade to keep the interior and fuel lines cool.

If you’ve tried these steps and continue to experience vapor lock issues, it might be best to consult with a qualified mechanic or automotive specialist who can diagnose the problem and recommend a specific solution for your vehicle.

How to prevent vapor lock?

To prevent vapor lock, do the following:

  • Set up an Electric Fan.
  • Make use of a Heat Shield.
  • Install a New Fuel Line.
  • Make use of a longer carburetor fuel line.
  • Include an Electric Fuel Pump.

Set up an Electric Fan

You can assist lessen the chance of vapor lock by installing an aftermarket electric fan. With cooling fans that run automatically, you can effectively reduce engine heat. Because we know that heat causes vapor lock, any strategy to lessen it is beneficial. Furthermore, if you can keep the gasoline lines cool, the engine should continue to run normally.

Make use of a Heat Shield

Heat shields are inexpensive and straightforward to install. This aftermarket component keeps heat away from fuel lines and other fuel-related components. In general, it is the preferred strategy for preventing vapor lock. You can even reuse the surplus material on other elements of the car. To safeguard the gasoline lines, use heat shields whenever possible.

Install a New Fuel Line

Because of the high temperature, the fuel line becomes clogged, preventing fuel from entering the chamber. You might be able to prevent the problem if you install a new gasoline line. When installing a new gasoline line, you should use as much insulation as feasible. After all, replacing it with the same gasoline line will not address the problem.

Make use of a longer carburetor fuel line

A longer line from the fuel system to the carburetor can also be beneficial. A longer line takes longer to heat up, so the longer the line, the better. Remember to insulate it as well. If the line does not heat up, the fuel will not evaporate and become clogged. This action can help the engine perform more smoothly and effectively.

Include an Electric Fuel Pump

Installing a low-pressure electric fuel pump in the system can assist prevent vapor lock. When the original mechanical fuel pump overheats, it’s time to make some system changes. This is a difficult process that may necessitate the assistance of an experienced specialist. It should, however, minimize the heat in the system, preventing vapor lock.

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Watch the video below to learn more


What is the vapor lock?

It’s a distinctly modern issue. Vapor lock occurs when fuel boils in your carburetor or fuel line. Vaporized fuel causes back pressure in your fuel system, preventing gas from reaching your engine. It usually happens after a car has been idling or turned off and then back on.

What causes vapor locking?

When the temperature of the fuel rises sufficiently to convert it from liquid to vapor, a vapor lock occurs. Fuel pumps are meant to move liquid rather than air, and the increased pressure inside the fuel lines prevents the fuel pump from keeping the gasoline moving.

What are the symptoms of vapor lock?

Fuel pumps are unable to move vapors, and vapor lock symptoms include stalling, limited power, and hard restarting with long crank times.

How do you get rid of the vapor lock?

Once the fuel system has cooled, you can help expel any remaining vapor by gently pressing the accelerator pedal (but not to the floor) while running the engine. When the engine starts, depress the accelerator pedal until the car runs smoothly, indicating that the vapor lock has been removed.

Where is vapor lock likely to occur?

As fuel is supplied to the injector nozzles to be sprayed into the intake manifold, vapor lock is most likely to occur in the fuel injector lines following the flow divider.

How do you prevent vapor lock on a plane?

Some common techniques to prevent vapor locking include rerouting fuel lines away from heat sources, fuel coolers, fuel pumps integrally mounted to fuel cells, and heat shields surrounding insulated fuel lines.

What is the difference between an airlock and a vapor lock?

A liquid flow restriction or total halt caused by vapor trapped in a high point of a liquid-filled pipe system is referred to as an airlock. Because the gas is less thick than the liquid, it rises to high places. This is known as a vapor lock or airlock.

What are two causes of vapor lock aviation?

This is common on aircraft with engine-driven fuel pumps that suck fuel from the tank(s) on hot days. Excessively hot fuel, low pressure, or extreme turbulence of the fuel moving through the fuel system can all produce a vapor lock.

And that’s it for this article, in which we talked about vapor lock. Also, the answers to the following questions were discussed:

  • What is a vapor lock?
  • Why does it happen?
  • What are the symptoms of vapor lock?
  • How to fix the vapor lock?
  • How to prevent vapor lock?

Hope it was helpful. If so, kindly share it with others. Thanks for reading; see you around!


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