Misfuelling is an innocent mistake that could happen to you. Be it putting in gas in a diesel engine or vice versa, the potential damages of misfueling may reach in the tens of thousands of pesos. It's a nightmare situation one wants to avoid at all costs.

However, what happens when it's too late? Don't panic as there are ways to reverse the possible damages that could be done to your engine. Here is a guide on what to do when your car is misfueled.

Misfueling: What to do when it happens

Diesel fuel in a gas engine

If you were able to notice that diesel is being pumped into your gas engined car, call the attention of the attendant and stop it immediately. Whatever you do, do not start the car.

Next is to have the fuel drained in your tank and, more importantly, have it cleaned. Any traces of diesel in your tank will clog up the fuel filter and eventually damage the fuel pump. Make sure that it is clean before getting it installed in the car.

The worst case scenario is having started your car with diesel in your gas-powered car. Normally, the car will splutter to a halt as diesel fuel is thicker than unleaded but by that time, the damage has been done.

Misfueling: What to do when it happens

There is now diesel present in your fuel injectors and have clogged up your fuel filter. For this, you will have to drain your tank and have it cleaned. On top of that, you will need a new fuel filter, an oil change and a new set of spark plugs. Just to be sure, have your fuel injectors cleaned but, for peace of mind, better to have them replaced. The same goes for your ignition coils. Again, it is vital that the fuel tank has been cleaned to avoid fuel contamination. Symptoms of a gas engined car with traces of diesel include backfiring, significantly blunted performance, worse fuel economy and the lack of response.

Misfueling: What to do when it happens

Unleaded fuel in a diesel engine

Like in a gas engined vehicle, it's best to stop the refueling process and immediately get the tank drained an cleaned. It's also worth emphasizing that you should not start the vehicle when the wrong type of fuel is loaded. If you do start the car, that's where it becomes more complicated as modern diesel engines run on more sensitive and vital parts. It also does far more damage to the vehicle's fuel system.

See that CRDI badge on your car? That means it runs on a common rail system, which is standard fare for a modern turbodiesel engine. Unleaded fuel is less viscous (slippery) than diesel fuel and if it reaches the engine, it removes the lubrication from your engine, leading to more damage. Think of it as an engine running without oil and you get the picture. At first, there will be a lot of smoke, followed by a significant decrease in performance and, eventually, the engine will grind to a halt.

Misfueling: What to do when it happens

More importantly, the lines in the common rail systems have extremely fine tolerances and unleaded fuel eats away the rubber seals, as well as the fuel injectors. At this point, the system is a good as broken and, needless to say, the results are catastrophic.

To repair this, replace the injectors, fuel filter, fuel pump and the fuel rail. Do note that this is a very expensive repair, almost up to Php 100,000, depending on the vehicle. It is also worth mentioning that misfueling is generally excluded from car insurance policies, making this a very costly mistake.

Misfueling: What to do when it happens


In case the wrong type of fuel was pumped into your car, the station should be accountable under normal circumstances; as there is a presumption of competence, opines our legal adviser. That means if you asked the station attendant to fill your car with unleaded fuel, and they accidentally pump in diesel; they could be liable for damages. But if you're the one who asked for the wrong fuel, then it is your fault.


In some gas stations, the nozzles for unleaded and diesel are different while some manufacturers are taking steps to prevent these incidents from happening. Some cars have different fuel nozzle openings only to accommodate the correct type of nozzle. However, not all have adapted to this system so you have to be careful.

The best way to avoid this innocent but expensive error is to always be aware. Clearly state the type of fuel you want loaded in your car. Standard operating procedure for station attendants is to tell you the type of fuel being filled, giving you time to correct the attendant. Just to be sure, take time to look at the nozzle being inserted into the fuel filler. These few extra steps will save you the hassle, as well as repair costs.