Wrong Fuel in Your Car: How Much Will the Repair Cost?

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Putting the wrong fuel in your car is more common than many drivers realize. It can happen easily when you are in a hurry, tired, or using multiple vehicles. Whether you accidentally put gasoline into a diesel engine or diesel into a gasoline engine, the consequences can vary greatly, and so can the repair costs. Some cases may cost only a few thousand baht, while more serious situations can escalate to tens of thousands.

What Happens When You Put the Wrong Fuel In

When gasoline is mistakenly filled into a diesel car, the impact is generally more severe. Diesel systems rely on the lubricating properties of diesel fuel, but gasoline removes that lubrication, causing metal components to wear rapidly. This can damage the high-pressure fuel pump, injectors, and other key parts. Symptoms such as rough idling, stalling, and failure to start are common. In the opposite situation—diesel in a gasoline vehicle—the damage is usually less dramatic, but still concerning. The engine may misfire, run unevenly, burn fuel improperly, or foul the spark plugs.

What Needs to Be Fixed

The level of repair depends heavily on whether the engine has been started. If not, the solution is straightforward: the tank simply needs to be drained and cleaned, which is inexpensive. However, once the engine runs, the wrong fuel circulates throughout the system. This requires a more comprehensive cleaning process. Diesel vehicles contaminated with gasoline often need the entire fuel system flushed, including lines, filters, and injectors. In more severe cases, the high-pressure pump may need replacement—a costly component. Gasoline cars contaminated with diesel typically require cleaning of the tank, injectors, and potentially replacing damaged spark plugs.

Estimated Repair Costs

Costs vary by vehicle model and workshop pricing:

Wrong fuel but engine not started

• Draining + tank cleaning → 1,000 – 3,000 THB

Engine started, minor contamination

• Fuel system flush + new filter → 3,000 – 8,000 THB

Severe damage (mainly diesel cars with gasoline contamination)

• Full system flush → 5,000 – 10,000 THB
• Injector replacement → 4,000 – 10,000 THB per injector
• High-pressure pump replacement → 20,000 – 60,000+ THB

In short: Repair costs may range from a few thousand to tens of thousands, depending on damage severity.

What to Do Immediately After Misfueling

The most important step is not to start the engine. Doing so keeps the wrong fuel from spreading through the system and prevents severe damage. After stopping immediately, inform the station staff and arrange for a tow to a workshop. Technicians can then safely drain and clean the system, minimizing the overall repair cost.

How to Prevent It

Developing the habit of checking the fuel type on your fuel cap before every refill is one of the simplest preventive measures. Avoid distractions such as checking your phone while refueling. For rental cars or shared vehicles, adding an extra label near the fuel cap can help prevent confusion.

Conclusion

Putting the wrong fuel in your car can lead to anything from minor inconvenience to major mechanical failure. Costs rise dramatically when the engine is started after the mistake, so quick action is crucial. With careful attention during refueling and awareness of the correct fuel type, drivers can easily avoid this costly e

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