【Car Tips】What problems will occur if you use the wrong oil

As the editor, I'll be breaking down the "problems of using the wrong fuel" from a Hong Kong driver's perspective in incredible detail, covering the consequences of misusing gasoline vs. diesel, the impact of using the wrong engine oil, why Hong Kong's environment requires special attention, and what to do if something goes wrong. Once you read this, you'll know why you shouldn't be careless when it comes to fueling your car.

1️⃣ What are the different situations of using the wrong oil?

What most Hong Kong car owners call "using the wrong oil" actually falls into two categories:

  1. Using the wrong fuel
    • Gasoline car filled with diesel
    • Diesel car filled with gasoline
    • Wrong gasoline brand (92/95/98)
  2. Using the wrong engine oil
    • Incorrect viscosity (viscosity grade)
    • Specifications (API/ACEA/factory certification) do not meet
    • Using an oil type that is not suitable for the engine (e.g. using gasoline oil in a diesel engine)

2️⃣ Consequences of using the wrong fuel (actual situation in Hong Kong)

2.1 Accidentally adding diesel to a gasoline vehicle

Most private cars and sedans in Hong Kong are gasoline engines. Once diesel is added, the following will occur:

  • Immediately affects combustion : Diesel ignition temperature is high, and the spark plug ignition of the gasoline engine cannot effectively burn diesel, resulting in engine shaking, smoke emission, and power loss.
  • Fuel system pollution : Diesel has high viscosity and will clog gasoline injectors and three-way catalytic converters.
  • White smoke/black smoke coming out of the exhaust : incomplete combustion and abnormal exhaust.
  • Once started, the spark plugs, catalyst and oxygen sensor may be damaged in a short period of time.

Editor's Tip : Fuel pumps at Hong Kong gas stations are not uniformly colored (different brands have different colors), making it easy to get confused at night or when you're in a hurry. It's best to check the pump label before use, rather than just looking at the color.

2.2 Diesel vehicles mistakenly filled with gasoline

In Hong Kong, diesel is mainly used in trucks, vans, and some SUVs:

  • Gasoline is highly volatile, which can reduce the lubricity of the diesel system and easily cause wear on the high-pressure fuel pump and fuel nozzle .
  • Imbalance in combustion temperature and compression ratio leads to insufficient power, abnormal noise and flameout.
  • In severe cases, the engine may overheat or cause the piston to explode.

2.3 Wrong gasoline brand (92/95/98)

Most private cars in Hong Kong are recommended to use license plate number 95 :

  • Use oil of lower specification (such as 95 to 92)
    → Engines with high compression ratios will experience knocking, which can damage the piston crowns and valves in the long term.
  • Use a higher specification (e.g. 95 to 98)
    → There is no immediate harm, but it has no obvious benefit to non-high-performance engines and may increase fuel costs.

3️⃣ Consequences of using the wrong engine oil (Common questions for Hong Kong drivers)

3.1 Viscosity Error

  • The car manufacturer specifies 5W-30, but you use 20W-50:
    → In Hong Kong in the summer, engine oil is too thick, resulting in high resistance during cold starts and high fuel consumption.
  • The car manufacturer specifies 10W-40, but you use 0W-20:
    → Under high temperature, the engine oil is too thin, the oil film is thin, and the metal wears quickly.

3.2 Specifications not met

  • Different factory certifications (such as VW 504.00, MB 229.5) may contain inappropriate additive formulas, causing carbon deposits, wear or catalytic converter blockage.

3.3 Using the wrong type of oil

  • Diesel engine oil used in gasoline vehicles: Some diesel engine oils contain high phosphorus, which will poison the three-way catalytic converter of general gasoline engines and make them ineffective.
  • Long-term use of incorrect engine oil will accelerate piston ring wear and valve carbon deposits .

4️⃣ Environmental factors that Hong Kong drivers should pay special attention to

  • High temperature + humidity → Cold start and high temperature lubrication requirements coexist, and the impact of using the wrong oil viscosity is greater than in cold regions.
  • Long-term short-distance driving → The engine oil is not heated thoroughly to evaporate the water, and the viscosity and formula requirements are high.
  • Frequent traffic jams → The engine idles at high temperature for a long time. The fuel quality must be stable, otherwise carbon deposits will form faster.
  • Driving frequently near the sea → Salt spray accelerates metal corrosion, making fuel and engine oil quality and stability even more important.

5️⃣ Hong Kong-style emergency treatment in case of using the wrong oil

Fueled incorrectly but not started

  • Please don’t drive!
  • Immediately call a tow truck to take the car to a garage/gas station, drain all the fuel in the tank, and then replace the filter.

Misfueling activated

  • Turn off the engine as soon as possible to reduce the scope of contamination of the oil system.
  • Empty the fuel tank → flush the fuel lines → replace the filter → check the fuel injectors/spark plugs/catalysts.
  • In severe cases, the oil pump and fuel injector need to be disassembled and cleaned, which costs thousands to tens of thousands of yuan.

Wrong oil added

  • If the viscosity or specification is incorrect, replace the correct engine oil and filter as soon as possible.
  • If it has been used incorrectly for a long time, you need to check the piston rings, valve oil seals and carbon deposits.

6️⃣ Editor’s Tips on Mistake Prevention in Hong Kong

  1. Develop a habit of checking : Before filling the tank, check the recommended model on the hood sticker or in the owner's manual.
  2. Don’t just look at the color of the petrol pump : the colors of petrol pumps at different petrol station brands in Hong Kong are not uniform, making it easier to make a mistake at night.
  3. Memorize the fuel brand and engine oil specifications required for your car .
  4. Digital maintenance record card : Use your mobile phone to record the engine oil used to avoid wrong oil when changing.
  5. Check the fuel specifications before long-distance travel or entering the mainland , as the mainland's fuel grade standards are different from Hong Kong (different grades correspond to different octane numbers).

7️⃣ Editor’s Summary

Using the wrong oil is not just a matter of whether your car can run or not. Sometimes, a single misuse of oil can cost you tens of thousands of dollars in repairs.
Fuel prices in Hong Kong are high, and if you add the wrong fuel, you have to pump it out and replace the filter, wasting both time and money.
What the car owner needs to do is to be clear about the fuel requirements of his car , slow down for a second when refueling, confirm the label and fuel port, and don't be too hasty.

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