Regan Brown
Vapor lock is a problem caused by liquid fuel turning into vapour in the fuel delivery system of gasoline-fuelled internal combustion engines. This disrupts the operation of the fuel pump, causing a loss of feed pressure to the carburetor or fuel injection system, resulting in a transient loss of power or a complete stall. It is more likely to occur when the vehicle is in traffic, as the temperature under the hood tends to rise. It can also occur when the engine is stopped while hot and the vehicle is parked for a short period. The higher the volatility of the fuel, the more likely it is that vapor lock will occur. This is why the type of fuel line is important to prevent vapour lock.
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What You'll Learn
Electric fuel pumps
Vapor lock is a problem caused by liquid fuel turning into a vapour while still in the fuel delivery system of gasoline-fuelled internal combustion engines. This disrupts the operation of the fuel pump, causing a loss of feed pressure to the carburetor or fuel injection system, resulting in a transient loss of power or complete stalling. Restarting the engine from this state can be difficult.
Vapor lock is more likely to occur when the volatility of the fuel is high. This is because the higher the volatility of the fuel, the more likely it is to vaporize. Modern fuel blends tend to have a lower boiling point than older fuel blends, making vapor lock more common today than in the past. The use of ethanol in modern fuels also increases the likelihood of vapor lock.
Vapor lock was more common in older gasoline-fuel systems that incorporated a low-pressure mechanical fuel pump driven by the engine. Such pumps were typically located higher than the fuel tank, were directly heated by the engine, and fed fuel directly to the float bowl inside the carburetor.
However, if an electric pump is installed in the engine compartment, it can act as a heat sink and cause a vapor lock. Electric fuel pumps are designed to push fuel and they lose efficiency when pulling fuel from the tank. Therefore, it is not recommended to bypass the mechanical fuel pump when an electric pump is installed. Instead, an inline pump can be used to back up the mechanical pump and prevent vapor lock during cold starts.
To avoid vapor lock, it is important to minimize the heat in the fuel lines. This can be done by using a black nylon braided fuel hose instead of steel lines, and routing the hose away from all heat sources. Additionally, a return system can be used to return excess fuel back to the fuel tank to cool down, rather than a returnless system that keeps fuel in the line where it can soak up excess heat.
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Thermal-barrier sleeves
Vapor lock is a problem caused by liquid fuel turning into vapour while still in the fuel delivery system of gasoline-fuelled internal combustion engines. This disrupts the operation of the fuel pump, causing a loss of pressure and, consequently, a loss of power or even complete stalling of the engine. The phenomenon is more likely to occur when the volatility of the fuel is higher, and when the vehicle is in hot environments or in traffic, where the under-hood temperature rises.
For vehicles where the fuel lines run close to the frame rails or floor pans, installing thermal-barrier sleeves may be challenging. In such cases, an alternative solution is to use sticky shields around the fuel tank to protect it from heat. This approach helps keep the fuel cooler and less susceptible to temperature changes that could affect fuel-pump operation.
It is important to note that while thermal-barrier sleeves can help prevent vapor lock, other solutions may also be required depending on the specific vehicle and operating conditions. These solutions include installing an electric booster pump near the fuel tank, upgrading to a larger-diameter fuel line, and ensuring proper ventilation and airflow around the engine to manage exhaust heat.
Additionally, the type of fuel used can also impact the likelihood of vapor lock. For example, ethanol blends have a lower boiling point, making them more prone to causing vapor lock issues. Therefore, selecting the appropriate fuel type and ensuring proper fuel system maintenance are crucial in preventing vapor lock.
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Ethanol-free fuel blends
Vapor lock is a problem caused by liquid fuel turning into vapour while still in the fuel delivery system of gasoline-fuelled internal combustion engines. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporize due to being heated by the engine, by the local climate or due to a lower boiling point at high altitudes.
Switching to ethanol-free fuel blends can eliminate vapor lock issues. Some users have reported success with this method, with no vapor lock or fuel issues even in high-temperature environments. Additionally, ethanol-free fuel blends can improve drivability and have a better smell compared to ethanol-laced fuel.
To prevent vapor lock, it is also important to consider the design of the fuel pump and fuel lines. Mechanical pumps should be avoided in favour of electric fuel pumps, as they are less prone to vapor lock issues. If a mechanical pump is used, stay away from steel lines, which offer no insulation from heat. Instead, use black nylon braided fuel hoses and route them away from all heat sources.
Overall, using ethanol-free fuel blends and making appropriate modifications to the fuel pump and fuel lines can effectively prevent vapor lock in gasoline-fuelled engines.
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Larger-diameter fuel lines
Vapor lock is a problem caused by liquid fuel turning into vapour while still in the fuel delivery system of gasoline-fuelled internal combustion engines. This disrupts the operation of the fuel pump, causing a loss of feed pressure to the carburetor or fuel injection system, resulting in a transient loss of power or complete stalling. Restarting the engine from this state may be difficult.
Vapor lock typically starts when an engine is shut down. As the engine is shut down, the heat rises up toward the fuel lines. Without air moving through the cowling, the fuel in the lines can start to vaporize. This is more likely to occur when the vehicle is in traffic because the under-hood temperature tends to rise.
To prevent vapor lock, it is recommended to use larger-diameter fuel lines. This is because larger-diameter fuel lines have a greater surface area, which allows for more effective heat dissipation. This helps to keep the fuel cooler and reduces the likelihood of vaporization. Additionally, larger-diameter fuel lines can accommodate a greater volume of fuel, which can help to absorb and dissipate heat more effectively.
Another way to prevent vapor lock is to use a return-style fuel system, where excess fuel is returned to the fuel tank to cool down, rather than a returnless system, which keeps the fuel in the line where it can soak up excess heat. It is also recommended to stay away from steel lines, as they offer no insulation from heat. Instead, use black nylon braided fuel hoses, which provide better insulation and should be routed away from all heat sources.
By implementing these measures, the likelihood of vapor lock occurring can be significantly reduced, improving the overall performance and reliability of the engine.
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Lower-volatility fuel
Vapor lock is a problem caused by liquid fuel turning into vapour while still in the fuel delivery system of gasoline-fuelled internal combustion engines. This disrupts the operation of the fuel pump, causing a loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. The higher the volatility of the fuel, the more likely it is that vapor lock will occur.
Aviation fuel is also manufactured with far lower vapor pressure than automotive gasoline to prevent vapor lock in aircraft, which are more susceptible due to their ability to change altitude and associated ambient pressure rapidly. Liquids boil at lower temperatures when in lower-pressure environments, increasing the likelihood of vapor lock.
In addition to using lower-volatility fuel, there are other ways to prevent vapor lock. One method is to use a return system, where excess fuel is returned to the fuel tank to cool down, rather than a returnless system, which keeps fuel in the line and allows it to soak up excess heat. Another method is to install an electric fuel pump, which can help prevent vapor lock by keeping the fuel-delivery system under positive pressure and running cooler.
Overall, using lower-volatility fuel can be an effective strategy for preventing vapor lock, especially when combined with other measures such as using a return system or installing an electric fuel pump.
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Frequently asked questions
Vapor lock is when the fuel in your fuel lines vaporizes, turning from a liquid to a gas. This disrupts the operation of the fuel pump, causing a loss of feed pressure to the carburetor or fuel injection system, resulting in a transient loss of power or complete stalling.
Vapor lock is caused by heat, which boils the fuel, preventing it from being pumped into the carburetor or fuel injectors. The higher the volatility of the fuel, the more likely it is that vapor lock will occur.
Vapor lock typically occurs during the summer months when high ambient temperatures, combined with the heat of a vehicle's engine and exhaust, are transferred to the fuel lines. It is also more likely to occur at higher altitudes or when stuck in traffic.
To prevent vapor lock, you can protect your fuel lines from getting hot by using a thermal-barrier sleeve on the lines, such as a Thermaflect Sleeve from Heatshield Products. You can also install an electric booster pump located inside or near the fuel tank, upgrade to a larger-diameter fuel line, or improve thermal management of exhaust heat.
Symptoms of vapor lock include rough-running, stumbling, and stalling with the application of throttle. Vapor lock is also rare during cold starts or in cold weather.
