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Will insurance cover def in diesel tank?

Putting Diesel Exhaust Fluid (DEF) into a diesel fuel tank can cause significant damage to the engine and fuel system. Whether insurance covers this type of mistake depends on several factors, including your insurance policy details and the circumstances under which the incident occurred. This guide provides detailed insights into the potential for insurance coverage, steps to take if this happens, and preventive measures.

Understanding Diesel Exhaust Fluid (DEF)

What is DEF?

  • Composition and Use: DEF is a solution of urea and deionized water used in Selective Catalytic Reduction (SCR) systems to reduce emissions from diesel engines. It is not a fuel additive and should never be added to the fuel tank.

Common Consequences

  • Engine Damage: Introducing DEF into the diesel tank can lead to contamination of the fuel system, causing significant damage to the fuel injectors, fuel pump, and other engine components. This contamination can result in costly repairs.

Insurance Coverage Considerations

1. Type of Insurance Coverage

Comprehensive Insurance

  • Accidental Damage: Comprehensive coverage typically includes accidental damage to your vehicle. If adding DEF to the diesel tank is considered accidental, it might be covered under this provision.

Collision Insurance

  • Not Typically Relevant: Collision insurance covers damage from accidents involving collisions, not misfuelling incidents.

2. Policy Details and Exclusions

Review Your Policy

  • Specific Exclusions: Check your policy for exclusions related to misfuelling or contamination of the fuel system. Some policies explicitly exclude coverage for misfuelling incidents.
  • Accidental Damage Clause: Look for clauses related to accidental damage or comprehensive coverage that may cover the costs of repairs.

3. Circumstances of the Incident

Intent and Negligence

  • Accidental vs. Negligent: Insurance companies may differentiate between accidental mistakes and negligence. Coverage is more likely if the incident is deemed accidental rather than due to gross negligence.

Steps to Take If DEF is Added to Your Diesel Tank

1. Do Not Start the Engine

Prevent Further Damage

  • Immediate Action: Do not start the engine if you realize DEF has been added to the diesel tank. Starting the engine can circulate the DEF through the fuel system, causing more extensive damage.

2. Contact Your Insurance Company

Report the Incident

  • Prompt Notification: Inform your insurance company about the incident as soon as possible. Provide them with all necessary details and documentation.
  • Claim Process: Follow their instructions for filing a claim, including submitting estimates for repairs and any other required paperwork.

3. Tow the Vehicle

Professional Assistance

  • Towing: Arrange for the vehicle to be towed to a qualified repair shop. Do not attempt to drive the vehicle to avoid further damage.

4. Repair Process

Qualified Mechanics

  • Professional Repairs: Ensure the repairs are conducted by a mechanic experienced in dealing with fuel system contamination. This typically involves draining and cleaning the fuel system, replacing filters, and potentially repairing or replacing damaged components.

Preventive Measures

1. Clear Labeling

Avoiding Misfuelling

  • Labeling: Clearly label the DEF and diesel fuel caps on your vehicle to prevent confusion.

2. Education and Training

Inform Drivers

  • Training: Educate all drivers of the vehicle about the importance of proper fuelling and the consequences of misfuelling.

3. Use DEF Carefully

Proper Handling

  • Separation: Keep DEF containers separate from diesel fuel containers to avoid accidental mix-ups.


Insurance coverage for adding DEF to a diesel tank depends on your specific policy and the circumstances of the incident. Comprehensive insurance may cover accidental damage, but it is essential to review your policy details and understand any exclusions. If this mistake occurs, avoid starting the engine, contact your insurance company promptly, and seek professional repairs. Preventive measures, such as clear labeling and driver education, can help avoid such incidents in the future. Always consult with your insurance provider for personalized advice and coverage details.

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