Contaminated diesel fuel can cause a variety of problems in engines. Some of the most common issues include:

1. Clogged fuel filters: Contaminants in diesel fuel can clog fuel filters, which can restrict fuel flow and cause the engine to run poorly or stall.
2. Reduced fuel efficiency: Contaminants in diesel fuel can disrupt the combustion process and reduce fuel efficiency, resulting in increased fuel consumption and emissions.
3. Corrosion: Certain contaminants, such as water, can cause corrosion in the fuel system, which can lead to leaks, fuel injector failure, and other problems.
4. Engine damage: Over time, contaminants can cause damage to the engine’s internal components, such as the pistons, cylinders, and fuel injectors. This can result in poor engine performance, reduced power, and increased emissions.
5. Emissions issues: Contaminants in diesel fuel can also cause increased emissions, which can lead to increased pollution and potential legal issues.

To avoid these issues, it is important to use clean, high-quality diesel fuel that meets industry standards and to regularly maintain the fuel system. This includes regularly checking the fuel filters, draining any water that may have accumulated in the fuel tank, and checking for any signs of corrosion. It’s also recommended to avoid using fuels that are not compliant with the standard regulations like using reconditioned diesel, or using different types of fuels that are not suitable for diesel engines like gasoline.

If an engine is found to have been run on contaminated diesel fuel, it may be necessary to perform a complete fuel system cleaning and replace any damaged components. It’s always best to consult a professional mechanic or the manufacturer’s guideline to determine the best course of action.