Should You Add Fuel or Fuel Additive First?

[MacChristian]

Fuel additive should be added before refueling for the correct sequence. Fuel additive, commonly known as fuel system cleaner, is also referred to as gasoline additive or fuel treatment. Here are the functions of fuel additives: 1. Carbon deposits: Cleans carbon deposits. 2. Atomization: Improves fuel atomization. 3. Engine: Protects the engine. 4. Engine wear: Reduces engine wear. 5. Emissions: Eliminates black smoke and reduces emissions. Below is additional information on precautions when using fuel additives: 1. Purchase: Pay attention to purchasing branded fuel additives and avoid using those recommended by repair shops without consideration. 2. New cars: Do not rush to use fuel additives in new cars. 3. Driving habits: Do not rely solely on fuel additives to clean engine carbon deposits; pay attention to driving habits.

[Susanna]

I've encountered this issue many times before and didn't know better than to add it randomly. After using fuel additives for so many years, I've found that the sequence really matters. It's best to pour the fuel additive into the tank when it's almost empty, then immediately refuel. The force from the fuel nozzle helps mix the additive evenly. If you do it the other way around—adding fuel first and then the additive—it tends to settle at the bottom and doesn't mix well. Especially for cars with direct injection engines, uneven mixing can potentially clog the fuel injectors. My neighbor once took the easy way out and added it in reverse order, and later had to spend over 800 yuan at the repair shop to clean the fuel system. Remember, always follow the dosage specified in the manual for each maintenance cycle, and don't arbitrarily increase the amount—it can damage the catalytic converter.

[DelEmilia]

As someone who has tried seven or eight fuel additives, let me tell you—always add it before refueling! The principle is simple: pouring the additive into an empty tank allows gasoline to mix it thoroughly like a blender. Adding it to a half-full tank means it floats on the surface, dissolving poorly—reducing cleaning effectiveness and potentially triggering the engine warning light. Once, before a long trip, I lazily poured it into a half-full tank and ended up with sluggish throttle response on the highway and noticeable engine shudder at rest stops. Now I’ve learned: always bring a small bottle to the gas station and add it before fueling—quick, easy, and effective.

[VanNathan]

Twenty years of car maintenance experience: Fuel additives should be added before refueling. The design of car fuel tanks makes it difficult for liquids added later to mix properly. The most scientific method is to add the additive first and then use gasoline to flush it through. Doing it the other way around can cause the concentrated solution to deposit and corrode the fuel pump filter. This is especially important for large-capacity fuel tanks, and the operation should be done when the fuel level is at the warning line. Also, a reminder to everyone: don’t blindly believe in high-concentration formulas—excessive amounts can actually harm your car. I once repaired a Mercedes whose owner added double the recommended amount each time, resulting in completely clogged oxygen sensors and repair costs starting at 5,000 RMB. The key is to add the correct amount at the right intervals.

[StSara]

At the 4S dealership, we've encountered countless owners who added fuel additives in the wrong sequence. Fuel system cleaners are concentrated solutions with higher density than gasoline. If added afterwards, 90% of it will sink to the bottom of the tank, causing the fuel pump to draw undiluted additive. This may lead to perceived power loss in the short term and could corrode sealing rings over time. The correct method is to open the fuel filler cap and add the cleaner first, then immediately refuel before the liquid settles. A pro tip: perform this when your tank is at one-quarter capacity for optimal mixing. Remember never to wait until the fuel light comes on - sudden contact with cold liquid when the fuel pump is overheated may cause malfunctions.

[EleanorLee]

When I first bought a car, I also struggled with this issue and personally tested different sequences. Once, I added fuel additive to a half-full tank, and after driving on the highway, the spark plugs were covered in black residue, proving it was completely ineffective. Later, I switched to adding it before refueling and specifically observed the exhaust pipe dripping water, indicating significantly more complete combustion. From a physics perspective: When refueling, 40 liters of gasoline rush into the tank within 5 seconds, creating enough turbulence to thoroughly mix the additive. In a static state, mixing would take over half an hour, by which time the engine would have already started running. I recommend buying fuel additives with measuring caps to avoid incorrect dosage.