4 Common Myths About Fuel Level Sensor

Hello! My name is Šarūnas, and I’m working in Ruptela technical support department for more than 6 years. During these years, I’ve done quite many online and onsite trainings, and would like to share my knowledge in an upcoming blog post series Tech. Tips.

Getting accurate fuel data is one of the most frequent requests that we get. Fuel is one of the main expenses for fleets and companies want to use it as effectively as possible. The first thing in doing this is starting to monitor your fleets fuel data, and fuel level sensors (FLS) are the best way to do it.

However, fuel level sensors tend to be surrounded by myths and false assumptions. Most of it comes from simply not knowing facts or are based on previous bad experiences with fuel level sensors.

Here are the 4 most common myths about fuel level sensors:

  • EXPLOSION – Fuel tank will explode or cause a fire while drilling a hole in it.
  • ENGINE DAMAGE – Metal shavings, left after drilling, will damage vehicle engine.
  • LOW ACCURACY – Sensors have huge measurement variations and give inaccurate data.
  • NOT RELIABLE – Few days after the installation sensors stop sending data.

Let’s look deeper at each of these myths and check if they are correct or false.


Will fuel tank explode while drilling it? Everybody knows that when you combine fuel with fire, it gives a dangerous situation. But that does not directly apply to all kind of fuels.

Petrol is very explosive in all conditions, and that is a fact. But what about diesel? Even being quite similar to petrol in looks, diesel has very different properties, and it takes quite an effort to make diesel burn. Diesel fires in diesel engines only when it’s spread to very tiny particles by an injector and then these particles are affected by very high pressure.

When drilling a fuel tank for fuel level sensor installation, we neither have diesel particles, neither pressure. To show what it takes to make diesel burn with open fire, have a look at the video below.

So will fuel tank explode while drilling it? The answer is no (as long as it is diesel fuel).


Will metal shavings, that get into the fuel tank while drilling, damage the engine?

While being in a remote construction site, I noticed that the fuel tank does not even have a proper cap, and is covered with a piece of fabric. The view that I found inside that tank wasn’t surprising – the whole bottom was covered with dirt. Of course, that’s not a good example of how it should be maintained, but that machinery was working whole day long and seven days a week without any problems:

Fuel Tank 1
Dirt in Fuel Tank 1

The reason why the engine was not affected by all that mess is relatively simple – fuel filter. Fuel filters are used in all vehicles and machines because even if all refills are done in good fuel stations, in a while, some dust and dirt get into the tank. It is unavoidable, and that’s where a fuel filter steps in, not allowing to get any of that dirt into the engine.

Coming back to metal shavings, that gets into the tank while drilling it, the answer is simple – they are caught by fuel filter on the fuel line, and none of them reaches the engine. Our recommendation is to change the fuel filter about a month after fuel level sensor installation, and you will take all shavings out without any effect on the engine, or its performance.


Fuel level sensors are highly accurate if used correctly. After analyzing many installations done not by professionals, we saw 4 main reasons that cause poor accuracy. All of them can be easily managed just by paying a little more attention to details.

STRING TENSION. Tensioning copper string that’s inside FLS tube is an essential part when assembling FLS. If the string is not tensioned correctly, it gives spikes in fuel data. Just a highlight from FLS quick start guide that blue cap needs to be pressed, to give its internal spring energy, then wrap the copper string around while gently pulling it. After that is done correctly, a spring, that’s inside the blue cap gives a constant tension to the copper string, and it will do its job properly. To make sure that string tension is right you can hit FLS tube with finger and feel mild vibration on the tube, that’s similar to the feeling when a tensioned guitar string is touched:

FLS string tensioning 1

DRY CALIBRATION NOT DONE. After cutting FLS to fit fuel tank, so-called “DRY CALIBRATION” must be done. It is needed so that the FLS could measure its own new length and come back to its maximum resolution. Follow chapter 2 on page 9 in the Quick Start Guide for detailed instruction.

TANKS USED FOR SENSOR CALIBRATION. It’s quite common to use some leftover plastic tanks for FLS calibration. The problem is, that even if those plastic tanks/buckets have marks, that supposed to be showing fuel level in the tank, they are often not accurate at all.

In the picture below, you see a workaround, that was done in remote installation. The plastic tank was filled with exactly 20 litres in a fuel station, and a red mark was painted on it. If you compare it to original 20 litres mark, that is pressed on the tank, you see, that there is quite a significant difference between these two lines, and If you would proceed with the original mark for sensor calibration, you would never get good accuracy when filling in fuel stations. We recommend using dedicated fuel pumps with counters or special high accuracy tanks.


TRACKING DEVICE OR FLS SENSOR CONFIGURATION INCORRECT. It’s not uncommon to forget to set the final tracking device and FLS sensor configuration after finishing the hardest part before, but the configuration is as important as the rest of the parts. Before leaving installation place, data averaging in FLS configurator must be set to 64:

Configurator 1


It is no secret that some drivers do not like having tracking devices and fuel level sensors in their work vehicles. It simply prevents them from using company resources for their personal purposes or in other words, stealing.

Even if it sounds too simple, one of the most common reasons for FLS sensors to stop sending data, especially a day or two after installation, is disconnected sensor. Of course, the first thought is installers mistake or low-quality product, but with Ruptela FLS that’s not the case.

Just see a picture below, showing what we found when went to check “defective” FLS. Security seal was broken and the whole FLS disconnected. Always set new security seal, if original was broken:

Disconnected FLS

Thank you for reading.