MISFUELLING A CAR: What should you do if you accidentally put the wrong fuel in your car? 


Information kindly supplied by https://www.fuelfixer.co.uk/

About a third of a million UK drivers every year put the wrong fuel in their cars. Petrol in diesel cars, diesel in petrol cars (despite the diesel nozzle being too wide to fit a petrol filler) and, more recently, AdBlue in the diesel tank.

Older engines could cope with a small amount of this abuse, but one price of efficient modern engines is less tolerance for what goes in the tank. We’ve heard of main dealers charging up to £9,000 for removing the wrong fuel and replacement of components (hardly ever really necessary), but independent specialists will usually get you back on the road for less than £200, and no harm done. Some have 24-hour emergency response units, equipped to do the work rapidly at the roadside.

Besides the obvious problem of the engine not working with the wrong fuel, there can be consequences if it’s not dealt with quickly:

Petrol Cars: Diesel will not burn in a petrol engine. In fact it generally covers the fuel system, including the spark plugs, in a thin oily coat which inhibits sparking and combustion. With a mixture of petrol and diesel the car will smoke, and it can burn out the spark-plugs. The diesel can make its way into the oil sump and raise the oil level while thinning it out. This can lead to a lack of lubrication for the engine – much like actually running out of oil.

Diesel Cars: Petrol is corrosive in a diesel fuel system, attacking the rubber hoses and seals and the plastic fuel tank itself. It strips the lubricating effect of diesel fuel, and this can cause damage to the low pressure fuel pump, the high pressure fuel pump and the injectors.

But no matter the type of contamination, in most cases the car will simply cut out and refuse to re-start long before any of these “worst-case” scenarios.

Is it possible to misfuel a vehicle fitted with an anti-misfuelling device?

Unfortunately, yes. Most factory-fitted devices only work if the vehicle is filled up in a certain way. For example, Land Rover’s documentation says: “The passive misfuelling protection device may not activate if an incorrect petrol fuel pump's nozzle is only partially inserted. The driver is responsible for filling the vehicle with the correct fuel. The passive misfuelling protection device only reduces the risk of filling the vehicle with an incorrect fuel.”

Land Rover

In fact, independent specialist Fuel Fixer say they have seen more misfuelled Range Rovers since the introduction of passive misfuelling prevention devices. This could be because having the device often lulls the driver into a false sense of security, causing them to pay less attention when filling up and they often don’t seem to fully insert the nozzle.

If you have only put in a small amount of the wrong fuel can you just top it up?

Any amount of contaminated fuel will generally have some sort of detrimental effect on the vehicle. Higher contamination ratios will directly affect the running of the engine and are very noticeable in that the vehicle will splutter, lose revs, and generally run rough. A smaller amount of contamination may be less noticeable, but a small amount of petrol in a diesel car will lower lubrication and cause extra wear and tear on the fuel pumps, injectors, and exhaust sensors. If it doesn’t damage them outright, it can shorten their life-expectancy.

What should you do if you put the wrong fuel in your car?

Many insurers now include misfuelling cover as standard, or as a paid extra. Some of them will fix the car free of charge as a part of your cover, while others will just charge you your excess or a call-out fee – but check if it will count as a claim against you and affect your no-claims bonus. It might be cheaper to pay for a specialist fuel drain call-out – and the leading companies offer average attendance times of less than an hour.

Mobile services like this should include full decontamination of the fuel system, as well as a small amount of clean fuel to get you back to the petrol station.

Warranties and Guarantees

Many vehicle manufacturers don’t guarantee mechanical parts that have come into contact with the wrong fuel. This invites dealerships to replace them, whether they have actually been damaged or not. Because of this Fuelfixer has seen prices as high as £9,000 to fix a misfuelled vehicle.

Their advice is to have a specialist fuel drain company come to assess the vehicle – either through your breakdown cover or called directly. They will be able to tell you if any parts need to be repaired or replaced, and potentially avoid expensive and unnecessary repairs.

AdBlue Contamination

With more diesel vehicles now fitted for AdBlue, it is quickly becoming the second most common fuel contamination issue. Private motorists are often confused about what Adblue is, but even experienced truck drivers sometimes put it in the diesel tank by mistake.

There is a common misconception that AdBlue is a fuel additive. It very definitely is not. It is injected internally into the exhaust, and NOT into the fuel. Putting it into the fuel tank can, as it is mostly composed of water, have catastrophic effects on the fuel system.

What is AdBlue and what is it for?

AdBlue is a trade-name for the most popular Diesel Exhaust Fluid (DEF), now used in many modern diesel vehicles to reduce the amount of nitrogen oxides created by diesel combustion. It is composed of deionised water and urea and works by mixing with exhaust fumes to change them from nitrous oxide (NO2) to harmless nitrogen, water and carbon dioxide. More on What is Adblue?

How to use AdBlue?

AdBlue has its own tank on all vehicles which use it. In most cases the filler neck is directly adjacent to the diesel filler neck, so it is not uncommon to find drivers inadvertently pouring AdBlue into the wrong tank.

Although AdBlue is non-toxic to humans, it is very corrosive to metal and paint, so spillages should be avoided.

What to do if you put AdBlue into the diesel tank?

Don’t start the car – not even to move it off the filling pump. AdBlue in a diesel tank will sink directly to the bottom of the tank and will be the first thing pumped into the engine when the car is started.

If this happens then correcting the problem will most likely require that the entire fuel system is cleaned out, including replacing any fuel filters that have come into contact with the AdBlue.

While it is possible to do roadside decontamination on the majority of vehicles contaminated with AdBlue, there are a few cases that require more extensive work and need to be recovered to a garage for servicing.


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