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What Happens When You Keep Driving on Reserve?

What Happens When You Keep Driving on Reserve


Are you one of the drivers who like to gamble with your car’s fuel gauge by betting on “yellow”? If yes, you can rest assured you’re not alone in it. According to multiple research, both local and global, more than half of drivers decide to fill up their car’s tank only after the yellow fuel light on the dashboard starts blinking, while some of them continue driving, even with the fuel light constantly on.

Whether it be laziness or illogical thinking on how to save money, testing your car engine’s limits like this is bound to have an unhappy ending. Most times it ends with your car running out of gas, usually, in accordance with the good old Murphy, on a location where there’s no gas station in sight (which actually happens to be a less painful consequence), or in a breakdown whose repair requires hundreds or thousands euros worth of expense. The moral of the story is that driving on reserve is definitely a bad idea, thus, in an attempt to point out the potential consequences, we’ve prepared a list of them for you.

Running Out of Fuel

As we’ve already stated, the first danger of driving on reserve is a tank without a drop of gas. A large portion of drivers relies on the wrong assumption that, once the fuel light starts blinking, they’ve still got a few dozens of kilometers to go. So, where lies the problem?

First of all, fuel gauges, even in the most modern cars, are not precise measuring instruments due to the fact that their functioning is based on a relatively simple technology, the level of fluid, which is relayed to the gauge either electronically or via metallic strips and coils. It explains why the level of gas in your tank can fall or rise when the car is on a gradient.

Secondly, a fuel gauge does not always represent a fixed parameter and depends on a multitude of factors, such as the way you drive, which can be less economical or more economical, or the model of your car. For example, A Mercedes C-class can cruise along for an average of 74 kilometers after the fuel light goes on, whereas a Vauxhall Astra is likely to give up at 42 kilometers.

If you happen to think that being left on the road, with no sign of a gas station, is the biggest challenge you’ll have to face, in case of an empty tank, you’re sorely mistaken. That’s where the “fun” actually begins. An empty tank can cause serious damage to the seals, pumps and injectors in diesel engines due to the fact that, in the event of fuel shortage, they are forced to draw on air rather than a rich, oily mix of diesel and lubricant. When it comes to certain types of diesel engine, depending on the pump they use, in the event of an empty tank, the air fills it up, thus preventing the newly arrived gas from moving from the tank to the engine, which can lead to your car not starting. In that case, a professional car service intervention is required. When it comes to petrol engines, the situation is a little less harmful because they tend to “swallow” the air in the absence of fuel, which is why it’s important for the accumulator to have enough capacity to electrostart, in order to draw the newly arrived fuel.

What if your car breaks down somewhere on the road?


The Overheating of the Electric Pump Engines

When the car runs out of fuel, the engine starts to overheat and the windings begin to melt. 

Gas makes its way from the tank of a car to its engine via electric fuel pump. When you fill up your tank, gas enters the fuel pump through a part called the strainer and moves through another round pump before finally entering the electric pump engine to cool its copper windings. When your car is out of fuel, air cools the windings, instead of gas, which makes the engine overheat and the windings melt. This is why you’ll often hear experts talking about how a pump running on an empty “stomach” is not a good thing.

Along with the fact that it cools the engine, gas also lubricates its rotating parts, thus preventing the engine from wearing out.

The Corrosion of the Fuel Injection System

When your tank is empty for the most part, condensation kicks in due to the difference in temperatures, which causes the corrosion of the fuel injection system, which further leads to problems with your engine running properly. Transition weather periods are the ones to look out for, when the daytime temperatures rise above 10 degrees Celsius and the nighttime temperatures drop below 0 degrees Celsius. This particularly affects cars with tank volumes of up to 100 liters, which, as a consequence, turn into empty barrows full of condensate.

This problem becomes even more evident with older cars whose tanks are made of tin, unlike the tanks of modern cars, which are made of plastic. Tin, affected by the aforementioned condition, corrodes and mixes with the gas, which very often leads to a pump breakdown due to which, at high speeds which stimulate an increased fuel flow through the injection system, the car can simply cancel on you in traffic.

Clogging Up Filters

The less fuel there is, the bigger the concentration of residue inside the fuel tank.

Imagine you have a bottle of decent red wine…The residue found at the bottom of the bottle is something you certainly don’t want to drink, right? The same applies to cars.

Residue is a constant which increases by filling up your car with gas. In the event of a full tank, the concentration of residue is inconsiderable. For example, when it comes to a 50 or 60 liter volume, the concentration of residue of about 50 ml won’t cause any problems. However, when we drop to 5 liters of gas, the concentration of residue goes up by 10, which increases the possibility of the engine drawing residue. So, although residue is an unavoidable element of every tank, its concentration is smaller when there’s more gas in the tank, which prevents the filters and electric pump from getting clogged up.

When you’re running low on gas, the engine draws residue from the bottom of the tank, which clogs up the filters and electric pump. When this happens, driving your car becomes increasingly difficult because the engine isn’t receiving enough gas.

What if You End up Driving on Reserve?

In a nutshell, postponing your filling up duties, especially when you’re running low on gas, whatever the reason may be, can turn into a very unpleasant experience, which can end up with you having to pay a lot more (towing service, part repair and replacement) than you would’ve had to, had you filled up your tank when it was time to do so.

If you still happen to find yourself driving on reserve, seeing it as we’re all human and as such, we’re prone to occasional oversights, stick to the following instructions:

  • Drive economically while maintaining a speed of 64 to 80 kilometers per hour, where it’s allowed, of course, and avoid sudden braking and acceleration;
  • Try to maintain a speed which keeps your engine running between 2.000 and 3.000 revolutions per minute;
  • Turn off your engine during stops for the purpose of saving gas, but only if your stops are more than a minute long, seeing it as starting a car uses the equivalent of about a minute’s worth of fuel with the engine at 2.500 revolutions per minute.

We recommend that, when your fuel light goes on, which means that you’re dipping into your car’s reserve, you take it seriously. Its role is to draw our attention and it is precisely because of that that it first blinks rather than being on constantly.


We hope that you’ve found this article useful. For any questions, unknowns and suggestions you may have, please, feel free to contact us.