Wrong Fuel or AdBlue?

If you act quickly, it’s unlikely that you’ll face serious damage. In most cases, once we drain the wrong fuel, your car will be up and running again in no time.

It’s ideal if you haven’t started the car, as this means there’s almost no chance of damage. Even if you’ve started it and driven for a short while before noticing the issue, the risk of long-term damage is minimal. If you managed to get home but the car won’t restart, don’t worry—it’s still fixable, but be sure to call us to have the wrong fuel removed as soon as possible.

The longer the wrong fuel stays in your tank, fuel lines, and engine, the more harm it can cause. Over time, it can corrode rubber and plastic seals, damage tubes, and dissolve lubricating fluids.

It’s best not to attempt starting the car repeatedly or leave the wrong fuel in the system. Remember, petrol cars need petrol, and diesel cars need diesel—putting the wrong fuel in only creates problems.

The small amount of unmixed diesel left in your fuel lines, combined with the slightly mixed fuel in your tank, may allow you to drive a short distance. However, once the petrol moves through the low-pressure sender pump, the fuel lines, the filter (which holds about a pint of fuel), hoses to the high-pressure pump, through the pump, into the common rail reservoir, and then through the high-pressure lines to the combustion chamber, that's typically when the engine will stop. This is the point where the damage becomes evident—petrol in a diesel engine is problematic because it strips away engine lubricants and can corrode seals. To prevent further damage and allow you to continue your journey, the wrong fuel needs to be fully removed. In the past, people could siphon petrol out of their fuel tanks using a hosepipe, but modern fuel tank designs make that method impractical. Now, specialized equipment and expertise are required to do the job correctly.

Once the petrol travels through the low-pressure sender pump, the fuel lines, the filter (which holds about a pint of fuel), hoses to the high-pressure pump, through the pump, into the common rail reservoir, and into the high-pressure lines to the combustion chamber, this is typically when the engine will stop. Petrol in a diesel engine is problematic because it strips away engine lubricants and can corrode seals.

Unfortunately, some main dealers and garages see misfueling as an opportunity to profit. We’ve heard of cases where cars, with as little as twenty euros of the wrong fuel added and not even started, were collected from petrol station forecourts by main dealers. These cars were then subjected to unnecessary and costly repairs, including the replacement of expensive parts. While insurance might cover the costs, this can lead to the loss of no-claims bonuses or complications when selling the car, especially if you have to explain why it needed so much major work.

It’s not cost-effective for many garages to keep the specialist equipment we use to properly drain fuel from a car. For most, it’s easier and quicker to call us to handle the job.

It’s not recommended, but yes, you can try it. If it’s only a small amount of wrong fuel in a mostly full tank of the right fuel, you might get by. However, the engine will likely run poorly, and dashboard warning lights may appear, which will need to be reset at a garage. You might also find the engine won't start when cold. The risks include corrosion of rubber hoses, plastic seals, and potential damage to fuel pumps and engine components—repairs for which can be costly. Trying to dilute the wrong fuel is a gamble. It may work occasionally, but filling up the tank and risking damage makes it an expensive bet. It’s hit and miss whether you can get the car going or restart it the next day. As the saying goes: if you’re in a hole, stop digging. Calling us to fix the problem and get you back on the road is still likely your best and most cost-effective option.

Yes, it’s easy to mix up the fillers since they are often located next to each other. Many people mistakenly believe that AdBlue is a fuel additive, but it’s not. AdBlue is made up of one-third urea (which is acidic) and two-thirds deionized water. When this acidic solution mixes with your fuel and passes through your engine, the results can be damaging. Starting the engine only makes the problem worse. AdBlue is used to reduce nitrous oxide (a harmful gas) in the exhaust by converting it into nitrogen and water. A particulate filter further reduces solid particles from the exhaust. However, AdBlue is prone to crystallization, which can clog injectors and fuel filters. Filters exposed to AdBlue decompose quickly, much like cardboard soaked in water. The acidic urea and dissolved particles can damage seals, fuel lines, and injectors. It’s crucial to remove it quickly, ideally before the engine is started.

Yes, this was a common practice until the 1970s. Petrol could serve as an impromptu winter fuel additive for diesel in cold, remote areas like the Arctic.

Back then, diesel engines were simple and rugged, lacking the high-pressure pumps that make modern engines smooth and efficient. Today’s engines, however, are much more sensitive.

These days, Winter Fuel Additive is automatically added to diesel supplies by refiners as early as September, so there’s no need to rely on old tricks.