Katerina Swanson
Many people wonder if cars have a reserve fuel tank. While there is no separate tank, most cars have a reserve fuel capacity of 10-15% of the total tank capacity, which is enough to drive for 50-80km. This feature is designed to allow the driver to reach a gas station. However, driving on reserve is not recommended as it can cause serious damage to the engine.
Characteristics and Values of Reserve Fuel in a Car
| Characteristics | Values |
|---|---|
| Purpose | To allow the driver to reach a gas station |
| Quantity | Small volume, typically 10-15% of the total tank capacity |
| Distance | 50-80 kilometres after the reserve light shows up |
| Risks | Engine damage due to air entering the fuel system, corrosion, and excessive fuel deposits |
| Fuel Gauge Accuracy | Not precise due to simple technology and various factors affecting fuel economy |
| Recommendations | Refill the tank before reaching the reserve level to avoid issues |
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What You'll Learn
How much reserve fuel does a car have?
The amount of reserve fuel in a car varies depending on the model and age of the vehicle, as well as the size of the fuel tank, the engine, fuel efficiency, and purpose. In general, the reserve fuel level in most cars is about 10 to 15 percent of the total tank capacity. This equates to around 4-5 litres of fuel for a car with a fuel tank capacity of 40-50 litres.
It's important to note that the term "reserve tank" is not typically used in cars, but rather in commuter bikes. Bikes with a carburettor fuel system would instruct the rider to switch to the reserve tank when a certain amount of fuel was left in the main tank. This served as a warning that the rider needed to refuel soon.
In cars, there is typically not a separate reserve tank. Instead, there is a single fuel tank with two outlets. The main outlet is located slightly above the reserve outlet. When the fuel level drops below the main outlet, the car will start drawing fuel from the reserve outlet. This allows the car to utilise all or most of the fuel in the tank.
While it is possible to continue driving after the reserve light comes on, it is not recommended. Doing so can cause excessive fuel deposits to build up in the lower part of the fuel tank, potentially leading to engine damage. Additionally, driving with low fuel can be risky as fuel gauges may not always be accurate. It is generally advised to refuel once the tank reaches 1/4 of its capacity.
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What happens when you drive on reserve?
Driving on reserve can be risky. While the reserve setting simply allows access to all the fuel in the tank, rather than a dedicated secondary tank, it is still advisable to refill the tank before or soon after the level reaches the reserve outlet. This is because fuel gauges are not precise measuring instruments, and drivers can be left stranded if they assume they still have dozens of kilometres to go.
In addition, the fuel gauge does not always represent a fixed parameter and depends on various factors, such as driving style and the model of the car. For instance, a car can cover 50-80 kilometres after the reserve light comes on if driven at a perfect pace, but this distance can shed quickly with slow, aggressive, or rush-hour driving.
Furthermore, driving with low fuel can cause excessive fuel deposits to build up in the lower part of the fuel tank, potentially leading to damage in the engine. In diesel engines, an empty tank can cause serious harm to seals, pumps, and injectors as they are forced to draw on air instead of fuel. In some cases, the air fills up the pump, preventing new fuel from moving to the engine, which can be resolved only by a professional car service intervention. In petrol engines, the engine tends to "swallow" the air in the absence of fuel, which is why it is crucial for the accumulator to have sufficient capacity to electrostart.
Additionally, gas lubricates the engine's rotating parts, and without it, the engine can overheat and its windings can melt. When the tank is mostly empty, condensation can also cause corrosion of the fuel injection system, leading to further issues with the engine.
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Why you shouldn't drive on reserve
Driving on reserve fuel is not advisable due to several reasons. Firstly, it can lead to fuel pump issues. Fuel pumps require a constant flow of fuel to function optimally, and when the tank is in reserve, increased air enters the pump, reducing lubrication and causing overheating. This can result in pump failure, which is costly to repair or replace. Additionally, the fuel filter in the pump can become clogged with dirt, as dirt usually settles at the bottom of the tank and can be drawn into the system when the fuel level is low.
Secondly, driving on reserve fuel can increase the risk of being stranded due to running out of fuel. Fuel gauges may not always be accurate, and driving conditions can affect fuel consumption, making it challenging to predict how far one can drive before refuelling. This can cause inconvenience and leave drivers stranded in remote locations without easy access to petrol stations.
Moreover, running a car on low fuel can lead to the build-up of fuel deposits in the tank. Over time, these deposits can find their way into the engine, causing damage to injectors and other components. It is recommended to keep the tank at least a quarter full to prevent such issues and maintain the health of the vehicle.
In addition to these mechanical concerns, driving on reserve fuel can also impact safety. Running out of fuel in the middle of a journey can leave drivers stranded in potentially unsafe situations, especially if they are travelling in remote areas, at night, or in adverse weather conditions. It is always advisable to refuel before embarking on a long drive to avoid such scenarios.
Lastly, driving on reserve fuel can affect fuel price flexibility. By keeping the tank at least half full, drivers can take advantage of price fluctuations and refuel at lower prices. Running the tank low may lead to rushed refuelling decisions and less opportunity to benefit from cost savings.
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How to avoid running on reserve
Modern cars typically have a reserve fuel capacity of 10-15% of the total tank capacity, which is intended to be used in emergencies. This amounts to around 4-5 litres of fuel, which can take you several dozen kilometres—enough to reach the nearest refuelling station. However, driving on reserve frequently is not advisable, as it can cause damage to your engine and other parts.
- Refuel early: Try not to wait until the last minute to refuel, especially in autumn and winter. A good rule of thumb is to refill your tank once it reaches 1/4 full. This will help to prevent excessive fuel deposits from building up in the lower part of the fuel tank, which can lead to engine damage.
- Maintain a steady pace: When driving, try to maintain a steady pace as much as possible. Driving too slowly or aggressively, or in heavy traffic, can quickly deplete your fuel.
- Refuel regularly: While it may be tempting to push your car to its limits, infrequent refuelling can lead to breakdowns and reduce the longevity of your vehicle.
- Be mindful of safety concerns: When riding on reserve, the vacuum-operated valve that prevents fuel from flowing into the carburettor when the engine is not running is bypassed. This means that there is no protective barrier between the rider and a flooded carburettor.
- Consider purchasing a reserve fuel canister: If you are concerned about running out of fuel and being stranded in an unsafe location, consider purchasing a reserve fuel canister. This can provide you with enough fuel to get to a gas station.
By following these tips and staying mindful of your fuel levels, you can avoid running on reserve and help keep your car in good condition.
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What to do if your car runs out of fuel
Most modern cars don't have a separate reserve fuel tank. Instead, the fuel pump and sender unit are located inside the main fuel tank. As a result, the fuel gauge will usually display the amount of fuel remaining accurately. However, it's important to note that some vehicles may have a slight reserve, typically around 1 to 2 gallons, even when the gauge reads empty. This reserve fuel allows you to drive for a short distance until you can reach a gas station. If your car runs out of fuel, here's what you should do:
Firstly, it's important to stay calm and assess your situation. Pull over to the side of the road safely and turn on your hazard lights to alert other drivers. If you're on a busy highway or in a dangerous area, your safety is the top priority. Get your vehicle to a safer location if possible, such as an exit or a roadside stop.
Once you're in a safe location, you have a few options to consider. If you're close to a gas station, the best course of action is to walk or call for a ride to the nearest station and fill up a jerrycan or spare fuel container. This way, you can bring the fuel back to your car and refuel enough to get to a proper gas station and top up your tank. It is always a good idea to keep a jerrycan in your car, especially when going on long-distance trips or driving in rural areas.
If you're far from a gas station or in an area where getting a ride or walking is not feasible, you'll need to call for roadside assistance. This could be through your car insurance provider, an automobile club, or a dedicated roadside assistance service. They will be able to bring you a small amount of fuel to get you to the nearest gas station. It is always a good idea to have a roadside assistance membership, especially when embarking on long-distance drives or when driving an older car that may be more prone to breakdowns.
While waiting for assistance, it's important to stay with your vehicle. Lock the doors and roll up the windows if it's cold outside. If it's hot, you may need to turn on your air conditioning or roll down the windows slightly to keep the temperature bearable. Make sure to keep yourself visible to other drivers, especially if it's dark or during low-visibility conditions. You can use reflective triangles or flares if you have them, placing them a few feet behind your car to warn oncoming traffic.
Finally, once you've refueled your vehicle, it's a good idea to reset your fuel gauge by filling up your tank completely at the nearest gas station. This will help you keep track of your fuel levels more accurately and prevent similar incidents from occurring in the future. Remember to always plan your trips, keep an eye on your fuel gauge, and refuel before your tank reaches empty to avoid running out of fuel unexpectedly.
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Frequently asked questions
Reserve fuel is the small volume of fuel that is available once the fuel light comes on, allowing the driver to reach a gas station. This is usually around 10-15% of the total tank capacity, or 4-5 litres.
The reserve setting simply allows access to all the fuel in the tank. This is because fuel gauges are not always accurate and can give a false assumption of how much fuel is left.
Driving on reserve fuel can cause serious damage to the engine, as the lack of fuel can cause the engine to overheat and the windings to melt. It can also lead to corrosion of the fuel injection system.
In ideal conditions, a car can cover 50-80km after the reserve light comes on. However, this depends on various factors such as driving style, traffic conditions, and the model of the car.
