Wrong fuel in your car, what next?

You borrow a friend’s car to take your children to school but a few miles into the journey, the fuel gauge starts warning. At a fuel station, you realise the pump attendant has put the wrong fuel when the car refuses to start. Although this is a common mistake, as a driver, before you embark on any journey, it is important to know the type of fuel the car you are using consumes.

Isaac Igambi, a fuel attendant at Emma Oils Fuel Station in Kagoma, Wakiso District, says different cars have symbols or hints one can use to identify the type of fuel to use.

 “You can look for a sticker on either the car key, dashboard, near the fuel gauge, or behind the fuel cover/door of the fuel cup/tank. It is also good to read the manufacturer’s guide to know more about the car components, including the fuel it consumes,” Igambi says.

Types of fuel 

Most motor vehicles worldwide use petrol (gasoline) and diesel fuel types. The two types of fuel have different characteristics and properties. Diesel fuel is a type of liquid fuel that is commonly used in cars with diesel engines. The vast majority of cars that use diesel are modern heavy road vehicles that include trucks, buses and some passenger vehicles.

Diesel is generally thicker, with a higher energy density which makes the engine more fuel-efficient. It consists of hydrocarbons whose composition and properties are different from those of petrol fuel.

Petrol on the other hand is commonly used in internal combustion engines typically found in most cars. Whereas it is more volatile than diesel fuel, it has a high energy density which contributes to the vehicle’s performance and efficiency of the engine.

Petrol in a diesel car

Putting petrol in a diesel car will damage the car and its components.

Amos Matovu, a mechanic in Kawanda Town in Wakiso District, says the first sign of this mishap is the engine failing to start. Whereas petrol is less dense than diesel, petrol causes serious or potentially permanent damage to the engine. This will cause friction within the different parts of the engine which in turn damages the fuel pump and injector due to mixture of fluids. In most cases, once you start the engine, it dies on spot and sometimes, causes the battery to flatten.

In situations where the car even runs at all, the engine will make knocking noises and due to increased friction, the car will experience reduced power and performance until it cannot go any further.

Diesel in a petrol car

While diesel fuel does not combust the same way petrol does, in a petrol engine this can lead to incomplete combustion that also causes knocking and potentially damaging the engine’s pistons, cylinders, and valves. If the car manages to start, there will be a lot of exhaust smoke, a sign that there is a problem.

Because diesel is thick and has a greasy component, adding it to a petrol car leads to clogging of the fuel filter which leads to reduced acceleration and stalling os the engine.

What to do

The extent of damage varies depending on the mechanical condition of the car, how quickly the issue is addressed, the amount of incorrect fuel used, and the make and model of your vehicle.

In both cases, the key is to prevent further damage and ensure the vehicle can run safely with the correct fuel. Matovu says the first step is not starting the car at all.

“Once you realise that you have put the wrong fuel in your car, do not start. Instead, seek immediate help from a mechanic,” he adds.

Although removing the wrong fuel is a bit tricky and needs careful consideration, Matovu says it is important to follow particular steps to ensure other car components are not damaged.

Drain fuel tank

The first step is to remove the contaminated fuel from the fuel tank.

“Before draining the fuel tank, disconnect the negative terminal of the car battery to avoid any sparks. You should also disconnect the fuel lines from the fuel pump,” Matovu advises.

While the fuel pump can be accessed from beneath the rear back seat, disconnect the fuel lines that lead to it, the filler line from the fuel tank, and unbolt the straps that hold the tank. Carefully remove the tank and place it on the ground.

Spin lose the metal ring that holds the pump by twisting it clockwise using a hammer and a socket and then remove both the fuel pump and the fuel line. Drain the wrong fuel into a waste bin and use a towel to soak out the remaining fuel until the tank is dry. Then, wash the tank with soap and water and let it out to dry.

Clean fuel system

After draining the tank, several components including the fuel tank itself, fuel lines, pump, rail and the injectors. When cleaning the fuel tube from the tank cover, connect an air compressor and use clean water to flush out the wrong fuel through the filler hose that you disconnected from the fuel tank. Use a solvent such as Isoprophy alcohol (which is mostly used,) to flush out the water since this helps to evaporate the water remains out of the tube. Then, leave it to dry.

“When cleaning this line, do not add water. Rather, flush out the incorrect fuel into a waste can, and then fill up a filter connected to the line from the engine bay with a solvent and flush out using compressed air until the solvent is no more,” Matovu advises.

Finally, clean the fuel rail and injectors. Cleaning the rail is as simple as draining out the wrong fuel, flushing it with some air and letting it dry. However, to clean the injectors, use a plastic brush to remove dirt from the bottom and top of the injector. Connect a hose and a nine-volt battery to the bottom of the injector. Add alcohol to the hose and use compressed air to pressurise the hose while switching the injector on and off to force the alcohol out through it.

Before reconnecting the fuel system, depending on the extent of contamination, the mechanic may need to replace fuel and oil filters as well as the fuel pump assembly.

Refill and test

Once the fuel system is clean and any necessary repairs or replacements have been made, refill the tank with the correct type of fuel.

“Check for any leaks under the car or around the engine bay, connect the battery and finally do a road test for a few minutes to see if the car is running properly,” Matovu says, adding that one should also check for warning lights or error codes in the vehicle’s computer system.

How can motorists avoid misfuelling?

When a driver puts the wrong fuel in their vehicle, it is usually because they just are not paying attention.

Remember that the colour of the hose and nozzle is not always consistent.

If you at a fuelling station that you are not familiar with, do not just pick up the hose that is the colour you are used to using.

Be sure to read the signage properly; the pump should specify whether it is petrol, diesel, or something else.