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Misfuelling your car – a costly mistake

25/02/2015 by Jess Wallace in Safety

Putting the wrong fuel into your car can be a massive mistake. If the vehicle is driven, the engine can seize and parts of the fuel system may be destroyed. It can easily result in a write-off due to parts costs.

At Fleetcare, on average, a maintenance controller will take around 3 calls a week regarding misfuelling.

A diesel input hole in a vehicle is bigger than a petrol input hole, so more than likely these calls have been regarding a client misfuelling a diesel car. The pump for diesel is a lot thicker and often doesn’t fit into petrol engines however our maintenance team occasionally receives calls that this has happened. Often clients have just had a bad day, are in a rush or their minds are elsewhere.

Petrol Vs. Diesel. How do they work?

Diesel and petrol both have advantages and disadvantages when it comes to choice. It often depends on what the engine is being used for that will help the driver to decide what type of fuel engine would be best for the job.


Diesel is run off an internal combustion engine which uses glow plugs to ignite with heat compression. Diesel is a much heavier mixture and also very oily. Diesel engines have a lot more torque (pushing power) at lower revs and a diesel engine comes in both two stroke and four stroke versions.


Petrol engines use spark plugs to ignite and burn fuel to make an engine run. Petrol engines rev higher than a diesel engine. In most petrol engines, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection). Petrol engines must be geared lower to get the same torque as a diesel but since petrol engines rev higher, both will have similar acceleration speed.

What is the cost of misfuelling?

For those drivers that notice the fault before starting the engine, the cost to a business is around $460. This includes the costs to flush the fuel system and change the filters, not to mention the wasted fuel.

However, if you are unlucky enough to drive away from the petrol station with the wrong fuel, the cost to a business can be significantly higher. Should major repairs need to be done from the resulting damage, pricing can range from $4,000 to $17,000 depending on the vehicle and damage. Average repair cost for this unfortunate error is $7,000.

What are the steps you should take after putting the wrong fuel in your engine?

It happens to the best of us. A minor lapse in concentration and we have misfuelled our vehicle. Before panic sets in, and to help prevent any further misfuelling damage, Fleetcare has a few steps to keep you calm and deal with the situation that’s at hand.

  1. Do not start the engine at all. If you’re at a pump don’t even start the car to move away to allow the car behind you in.
  2. Tell the service station attendant about your error and pay for the fuel dispensed.
  3. Disconnect the battery before attempting to move the car. Switching on the ignition to release the steering lock may feed contaminated fuel to the injectors. Even a small amount of the wrong fuel in your engine can require dismantling of the complete fuel system and replacement of expensive components.
  4. Call your road-service provider or a removal truck to transport the vehicle to a mechanic where they can drain the tank, clean the fuel pump and replace any filters.
  5. If you don’t notice the error until the vehicle has been driven, stop as soon as you can and call for assistance. The longer you drive, the more damage you will cause to your vehicle.

Car warranty and misfuelling insurance

Some insurers do offer misfuelling protection, however it pays to check that this is covered in your policy. Most, if not all car warranties, don’t cover misfuelling.

If the error is caught before turning the engine back over, the vehicle can usually be towed, drained, inspected and saved. However, this would be at a cost to the driver – most insurance companies would not provide misfuelling cover in this situation nor would any car warranty.

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