Is It Safe to Drive With Contaminated Fuel in Your Car
Driving on contaminated fuel is never safe for any appreciable distance, but the level of risk depends on the type of contamination, how much was added, whether the engine was started, and which fuel system is involved. In all cases the common answer is to get off the road as soon as it is safe and call for professional help. Find out the first steps to take if you’ve put the wrong fuel in your vehicle.
Wrong Fuel Help Australia is there to assist you at every stage of a contaminated fuel incident. Some callers are drivers still at the pump who saw what happened immediately. Others come from drivers who have been on the road for some time before realising what’s happened. The difference in outcome between those two scenarios is significant and is directly dependent on whether and how long the vehicle was run on the contaminated fuel.
Why Stop the Engine Is Not Just Cautionary Advice
There is no cautionary language designed to be overcautious in the instruction to turn the engine off and not to restart it. That is the most important thing to do in any contaminated fuel situation because of what the engine does to the fuel system the second it runs.
This is why it’s usually much easier to recover a vehicle that has not yet been started than one that has already been driven, even if both have the same amount of contaminated fuel.
When the engine is running, the fuel pump pulls fuel from the tank, pushes it through the fuel filter, into the fuel rail and out through the injectors. This is a low pressure system on a petrol engine compared to a diesel. Fuel is delivered to a modern common rail diesel at pressures that can be in excess of 2,000 bar and diesel itself lubricates the pump and injectors as it passes through.
As soon as the engine starts running on contaminated fuel, that contaminated fuel gets into every part of the fuel delivery system. There is no longer a single point of containment. Now the contamination is in the filter, the fuel lines, the rail, and possibly the injectors. The difference between a tank drain and a total system flush is the stopping of the engine while the contaminated fuel is still in the tank only.
How the Risk Level Changes Based on What Was Put In
Petrol in a diesel engine
This is the worst case contamination scenario for driving. The lubricating properties of diesel are degraded by petrol and it’s these lubricating properties that protect the high pressure fuel pump and injectors in a common rail diesel system. When the engine runs on petrol-diesel mix every second the pump and injectors are being rubbed by friction the fuel was not designed to deal with at those pressures. Damage begins immediately on start up and worsens with each minute of running. Driving any distance on a significant petrol contamination in a diesel is a real outcome rather than a theoretical risk because it causes permanent damage to the pump and injectors. Discover the symptoms that show when petrol passes through a diesel fuel system.
Diesel in a petrol engine
Diesel in petrol engine has a different risk profile. Petrol engines use spark ignition, and diesel doesn’t burn well in that environment. The engine will normally run badly, misfire and smoke but the fuel delivery parts are not in the same immediate danger as a diesel system running on petrol. The main problems are fouling the spark plugs, possible damage to the catalytic converter from unburned diesel in the exhaust, and increasingly poor combustion performance the longer the vehicle is driven . The engine more likely to die and protect itself than silently accrue damage. Read our guide to what happens if you put diesel in a petrol car.
AdBlue in a diesel fuel tank
The chemistry of AdBlue is such that a wrong fuel scenario is treated differently to AdBlue in the diesel fuel tank. AdBlue is heavier than diesel , so it sits at the bottom of the tank where the fuel pump draws from . When mixed with diesel, the urea starts to crystallise, and those crystals are abrasive. Driving with AdBlue contamination in the diesel tank is dangerous even before the engine is started. Once the fuel pump begins drawing from the tank it is pulling an abrasive mixture through components with micron level tolerances. AdBlue contamination needs to be treated immediately, whether or not the engine was started.
The Short Distance Question: When Moving the Vehicle Is Reasonable
This is the question most advice on contaminated fuel avoids answering directly, so here is the honest answer.
If the contaminated fuel has been introduced and the engine has not been started and the vehicle does need to be moved a very short distance, e.g. from in front of a fuel pump to a safe area in the forecourt car park, then pushing the vehicle manually or moving it in neutral is the correct approach where physically possible. Most modern vehicles have an electric fuel pump and on some models it will turn on when the key is turned to the accessory position even if the engine is not started. Before doing anything, check the key with the technician.
If the engine was started briefly and the engine stalled and the vehicle is in an unsafe location, such as in a traffic lane, moving the vehicle a short distance to safety is a reasonable decision. Then the damage caused by a few seconds of movement is smaller than the danger of staying in the road . It’s a pragmatic judgement call, not a recommendation to drive on.
What isn’t reasonable is driving to the nearest mechanic under the assumption that a short distance is fine. The closest garage could be kilometres away. On a diesel vehicle, several kilometres on petrol contamination, the conversation about damages changes significantly.
Our step-by-step guide covers the proper sequence from pump to call to recovery for the immediate steps to take from when you realise the mistake.
What Happens to the Fuel System Every Minute You Drive on Contaminated Fuel
The cumulative damage from running contaminated fuel plays out in a predictable fashion.
Contaminated fuel is fed to the fuel pump during the first few seconds of engine operation. The absence of the lubricating properties of diesel starts immediately in a diesel system. In the first minute of driving contaminated fuel has gone through the fuel filter, through the fuel rail, and through the injectors. The filter is dirty now, it needs to be replaced. In the first few km the high pressure pump in a diesel system has been running loaded with insufficient lubrication. Metal particles start to build up in the filter and on injector seats.
After a few kilometres, particularly when loaded or on a highway with higher fuel consumption and injection rate, the damage profile changes from potentially recoverable to more and more likely permanent damage to at least some fuel system components. This is where a fuel drain is not enough and a full mechanical assessment is required along with the drain.
For the symptoms that tell you contamination has already reached the fuel system we have a guide to diesel misfuelling symptoms that covers each warning sign and what it means about how far the contamination has spread.
The Hidden Danger: When Driving With Contaminated Fuel Feels Normal
One of the more deceptive things about contaminated fuel situations is that sometimes, especially if the proportion of contamination is quite low or the tank is large, the vehicle will run normally for some distance before any symptom occurs. This is not a signal that the situation is safe. It’s a sign that damage is accumulating in silence.
A vehicle with a large diesel tank & a relatively small amount of petrol may be driven tens of kilometres before any symptom occurs. The petrol diesel mixture is passing through the pump and injectors all that distance in a diluted form. The lubrication reduction may be partial, not total, but it is still reduction. The wear is increasing more rapidly than if you were running on clean diesel and the damage is cumulative over every kilometre.
That’s why the recommendation to stop and call for help remains even when there are no symptoms. Lack of symptoms does not prove that no damage is occurring. It’s confirmation that the damage has not yet reached the point where the engine management system sees it.
After the Engine Has Already Been Started: What Changes
If you are reading this and the engine has already been started and run some distance, things have gone beyond a simple drain. The contaminated fuel is now spread throughout the fuel system. At the very least the filter will need replacing. On a diesel vehicle, the pump and injectors need to be assessed.
This is not a cause for panic, but it is a cause for realism in terms of what the recovery entails. If the engine has been run after misfuelling, a professional assessment will include a fuel system pressure check to determine if the pump is delivering the correct pressure, a diagnostic scan for fault codes relating to injection and a physical inspection of the filter for metal particulate. The scope of repairs outside the drain depends on the results.
Our guide on permanent misfuelling damage explains the thresholds and what makes damage irreversible because when driving on contaminated fuel crosses into permanent engine damage.
If you have contaminated fuel in your vehicle and you are not sure what’s going on, contact Wrong Fuel Help Australia immediately. If the engine has been turned off, do not turn it back on. Open for business 24/7 in Newcastle, Central Coast, Lake Macquarie, Maitland and the wider Hunter region. Ring Jay direct on 0432 553 905 or contact us through wrongfuelhelp.com.au.
Frequently Asked Questions
Can I drive just a short distance to get to a mechanic?
No, if it can be avoided. Even a short drive can spread contaminated fuel through the fuel system, especially in a diesel engine. If the vehicle is already in a safe location, switch the engine off and arrange professional fuel recovery instead of driving to a workshop.
What if I only added a small amount of wrong fuel?
A small amount of wrong fuel reduces the immediate risk but does not remove it. Petrol in a diesel system can still reduce lubrication, while diesel in a petrol engine can affect combustion. A professional assessment is the safest option before driving further.
What if the engine is running fine after wrong fuel?
Not necessarily. Some vehicles continue running normally even though contaminated fuel is circulating through the system. Damage may still be developing, particularly in modern diesel engines. Do not assume it is safe to continue driving simply because no warning lights have appeared.
Is diesel in a petrol car less dangerous to drive on?
Yes, diesel in a petrol engine is generally less damaging than petrol in a diesel engine. However, it can still cause poor combustion, misfires and catalytic converter damage. The vehicle should still be professionally drained before further driving.
Does calling a mobile drain service mean I have to wait?
Most mobile fuel recovery services respond as quickly as possible and perform the drain onsite. Waiting for a specialist is usually faster and safer than arranging a tow and workshop repair.
