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Help, I've Put Petrol In A Diesel Engine - FAQ

Last Edited: 22/01/2015
In this guide:

    Noticed Your Error At The Petrol Station?

    Do not start the engine, don't put your keys in the ignition, and do not unlock the car! If you turn the key then you could prime the fuel pump and therefore contaminate engine components. This can occur even if you don't turn the key all the way.

    Some modern cars also prime the fuel pump when you simply unlock the doors. So before doing any of these things, call a breakdown assistance service and wait for them to come and pump all of the fuel out of your tank. You can then fill up properly and be on your way.

    Have You Noticed Your Error After You've Left The Forecourt?

    We'll assume your reading this having noticed your mistake and pulled over on the road. Ensure you have left your vehicle in a safe location, since it's not as bad to wreck your engine than it is to put your life, or the lives or others at risk. Remember that if you are on a motorway, ideally you should park next to one of the emergency phones which are located at 1 mile intervals.

    You should put your hazard lights on, and if it's dark leave your sidelights on too. It's wise to stand on the verge so that you are well out of the way of fast moving traffic. From here you can call a breakdown service, but remember to always face the traffic when you're using the phone. If your car is under warranty, you could invalidate the warranty unless you let the manufacturer fix the problem. Bear this in mind before calling in a local breakdown company and letting them do any work on the car, it could cost you more in the long run.

    Have You Called The Breakdown Company And Gasped At The Price Of Rescue?

    It's still probably best you pay them and avoid wrecking your engine. However, theoretically if you were near empty and you only squirted in a small amount of wrong fuel, you could then completely fill the tank with the correct fuel and be on your way.

    Some engines are known to handle up to 10 per cent contamination, so if you only added 1 litre of the wrong fuel and still have space for 50 litres of the correct fuel you could risk it.

    This, however, only realistically applies to petrol-run cars. On the other hand, even a little contamination is enough to wreck modern common-rail diesel (CRD) engines for example. Check your vehicle handbook if you're unsure, or call the manufacturer and get their advice.

    Disclaimer: We take no responsibility for your actions. We are not trained mechanics. These tips are provided as a guide, bringing together advice from around internet and various forums. You should always seek the advice of a trained vehicle mechanic or breakdown service when dealing with car maintenance issues such as this.

    Are You Unsure If You Have Misfuelled?

    Aside from the obvious, i.e. checking your receipt, here are some other symptoms you can look out for:

    The vehicle is difficult to start, especially when the engine is warm

    The engine gets very noisy under load

    Your exhaust is smoky when driving

    The engine won't stop once started

    Sudden loss of power

    Complete loss of power

    Do You Need Cheering Up?

    If it makes you feel any better, past research has indicate that incidents involving a diesel car being accidently filled up with petrol actually occur fairly often as many as 400 times a day. Subsequent repair charges range from a few hundred to several thousand pounds.

    A report in 2014 showed that the british police force spend around £300,000 a year as a result of officers not paying attention at the pumps, which is an average of 4 police cars damaged per day!

     

    Preventing Misfuelling

    There are a range of simple yet vital questions you can ask yourself before making a trip to a fuel station.

    For instance, have you checked if the car you're driving is a petrol or diesel model? This is particularly relevant if you're using a hire car or company car.

    Is everyone who drives your car aware of what type of fuel it uses?

    Have you (if necessary) labelled your fuel tank with a 'Diesel Only' sticker?

    Do you double-check fuel pumps at petrol stations? Green often but does not always mean unleaded, while black may not mean diesel, especially when driving abroad! Remarkably, they're the opposite way around in some countries.

    Think you might have filled up with unleaded? Your receipt should tell you.

    If you are attempting to dilute unleaded petrol with diesel ensure your car is not a modern common-rail diesel. If it is then do not even consider diluting.

    It should only be possible to dilute 10 per cent of unleaded or under. Make sure you know the capacity of your fuel tank and make a judgement about whether it's worth the risk.

    You may be able to drain a fuel tank yourself but if in doubt seek expert help. There are specialist companies that will come to your house and drain your fuel tank.

    How Does The Wrong Fuel Type Affect Engines?

    Breakdown organisations put the estimate figure of petrol misfuelling incidents at around 150,000 cars a year, with repair bills totalling hundreds of millions of pounds. Petrol strips a diesel engine of the lubricant it needs to keep it ticking over, as well as damaging seals. It will almost always lead to the engine seizing, by which point the whole engine block and many vital components will likely be destroyed beyond repair.

    To make matters worse, pre-ignition systems start fuel pumps in new diesel models when car doors are unlocked. This reduces the time it takes for new diesel engines to warm up, but means that diesel engines can be ruined simply by unlocking the doors. Modern technology doesn't always help when it comes to human error.

     

    How Much Will This Mistake Cost?

    Brace yourself. If you've avoided turning on the engine or stopped quickly after turning on the engine, a fuel-tank drain may be sufficient. This can cost anywhere from £130+. It really depends on the area you've misfuelled in, and therefore which breakdown companies are within range. Don't be surprised if you're charged more if you're somewhere remote, as you're paying for their hourly rate inclusive of the time taken to reach you, as well as for safe disposal of your tank full of contaminated fuel afterwards.

    If you've driven the car after misfuelling, it is going to be costly. Vital components will be damaged, and unless you're driving a go-kart the bill for repair will easily stretch well into the thousands.

    Am I Covered On My Breakdown Cover?

    Misfuelling will not be covered by your manufacturer, though they may help tow your car to a dealership for you.

    Am I Covered On My Insurance?

    Misfuelling is generally excluded from all car insurance policies, including those which offer comprehensive protection.

    What If I Lease My Car?

    You will have to meet the cost of any repairs yourself if your car's on PCP or contract hire - or any other form of leasing contract. Misfuelling and then firing up your engine really is about the worst thing you can do to your car, so expect bills of at least several thousand pounds for a replacement engine and fuel system.

    Will My Warranty Be Invalidated?

    That probably depends on the amount of damage. Your manufacturer may threaten to invalidate your warranty on your fuel system and related parts unless you let them do the repair work, but there may be room for negotiation.

    Can I Dilute The Petrol With Diesel?

    Diluting contaminated fuel may be possible on older cars that lack the fine, high-pressure diesel injection systems of modern diesels. However, this is a high-risk move which could result in the destruction of your engine.

    It may be possible to dilute a proportion of petrol to diesel under 10% in older cars, though there's no guarantee this will work. Your car may run roughly for a while and you may risk long-term damage that is not immediately apparent.

    We don't recommend you try this but if you do risk it you need to be completely sure about your car's fuel tank and engine system - try this on a common-rail diesel and you'll simply wreck your engine.

    How Does This Mistake Happen?

    Modern diesel engines can be hard to differentiate for drivers with an untrained eye, or ear. Where traditionally diesel engines were clattery, dirty and slow to warm up, modern diesels drive and sound very similar to petrol engines. People simply forget they are driving a diesel as the associated audio and visual clues are simply not there.

    In light of the dash for diesel manufacturers are turning their attention towards the problem of misfuelling.

    Ford has been the first manufacturer to develop technology designed to prevent a misfuelling mishap, with its Easyfuel system, which prevents drivers filling up their diesel models with petrol.

    An unleaded petrol pump nozzle cannot enter a diesel tank on Mondeo and Focus models equipped with the system. Typically diesel nozzles are too wide to fit into any petrol tank, so the problem rarely crops up.

    To make matters more confusing the increasing uniformity of petrol pump colours does not provide motorists with a visual cue as to the fuel type.

    Whereas diesel pumps were traditionally black, unleaded petrol green and four-star leaded petrol red, modern-day diesel pumps are often green to enhance fuel suppliers' eco credentials, with BP being the most notable culprit.

    With the massive rise in popularity of diesels misfuelling is an inevitable and growing problem which is only just starting to be addressed by manufacturers.

    Diesel In A Petrol Engine

    Theoretically it should be hard to fill a petrol tank with diesel, as diesel nozzles are too wide to fit into the tank. However using diesel in a petrol engine may destroy the engine's catalytic converter, necessitating a costly replacement.

    How Much Biodiesel/Ethanol Can I Safely Put In My Car?

    If you've accidentally filled your tank with biodiesel or ethanol the likelihood is you'll need to drain your tank, unless your car is correctly modified to receive these fuels.

    What Else Can I Do To Prevent This?

    Aside from buying a Ford model with the Easyfuel protection system, the best thing you can do is to clearly label your vehicle with a sticker above the petrol tank, as car-hire companies generally do. This is particularly important if your car is used by a number of drivers. You can also buy little gadgets which you stick inside your fuel flap that are light activated, and shout out "Diesel, Diesel...." when you open the fuel cap.

    Until manufacturers work with fuel suppliers to address the issue, it's simply a case of having your wits about you and bearing the astronomical repair costs in mind.

    Efforts to introduce such a system by BMW across its model range suggest that manufacturers are intent on tackling the problem. Otherwise, you could always buy an electric car and never have to worry about this problem again.

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