Accidentally Fueling a Diesel with Gasoline

Can gasoline harm a diesel engine?

Pumping diesel gas
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Yes, most diesel fueling pumps are distinguished by green markings and green fueling nozzle handles, although some may use yellow as they do in Canada. And yes, the inside of diesel vehicle fuel doors has a “Diesel Fuel Only” label.

But what happens if you inadvertently fill your diesel car or pickup with gasoline?

Whether you’re new to diesel ownership, or might have both diesel and gasoline powered vehicles in your own personal fleet, it can be oh-so-easy to accidentally mis-fuel your diesel tank with gasoline.

Filling a fuel tank is such an ordinary and mundane task, that just a moment’s inattention (did you really need to read that text message?) can cause you to grab the wrong nozzle and pump away.

Bad enough if you realize the mistake right away and can get the car towed to a car dealership or independent repair shop to have the tank drained — a $500-$1,000 expensive nuisance.

But what if you don’t even realize the mistake and end up driving away with a tank full of gasoline? Chances are you won’t get very far, perhaps just a mile or so. That’s when the diesel in the fuel line gives way to the fresh batch of gasoline on the way from the tank, and the engine starts to run “funny.”

Of course, it all depends on how much diesel remained in the tank before the gasoline was added, and how new and sophisticated the diesel engine is.

In a 2007 or newer “clean diesel” engine, any amount of gasoline will probably damage the sensitive emissions control components (DPF, OxyCat and SCR) and system.

In older engines with much less sophisticated emissions systems, a lightly diluted (say 90 percent diesel/10 percent gasoline) mix would likely pass through with little or no detriment. It might simply cause reduced engine power, perhaps a bit more noise, and possibly a sharp warning from the emissions sensors that detect something other than pure diesel exhaust.

It’s a high concentration of gasoline that spells real trouble. Whether a modern clean common rail diesel (CRD) or an old indirect injection unit, burning straight gasoline or highly diluted diesel fuel will almost certainly result in catastrophic damage to the mighty diesel engine.

 Dos and Don’ts

If you are fortunate enough to discover you were pumping gasoline rather than diesel before driving away, here are the dos and don’ts.

  • DO NOT start the engine, even just to move the car from the pumps.
  • DO NOT turn the ignition on, even just to unlock the steering wheel. This could activate an electric fuel pump and feed tainted fuel into the engine injectors. DO tell the station attendant you cannot move the car and pay for the fuel dispensed.
  • DO call your roadside service provider and request a tow to either the vehicle’s brand dealership or an independent repair shop.
  • DO have the fuel tank drained and receive confirmation that the contaminated fuel was limited to the fuel tank.

If you don’t notice the mis-fueling error until the car has been driven, stop as soon as it is safe and call your roadside service provider to request a tow. Unfortunately, the price to repair the damage will be very expensive and this is a situation that will not be covered by your automaker’s warranty.

So What Does Gasoline do to a Diesel Engine?

The problem is multifaceted. It is a function of the completely different burn characteristics of the fuels (volatile and explosive gasoline versus high flash point diesel fuel), and the peculiarities of engine design in regards to how fuel is ignited (spark ignition versus compression ignition).

Gasoline is formulated to resist auto-ignition in a spark engine (see octane), so this fuel introduced into a diesel engine either won’t ignite or will more likely ignite at the wrong time causing severe detonation.

Though diesel engine reciprocating components — pistons, wrist pins and connecting rods — are built to withstand enormous explosive force, the shock wave effects of uncontrolled detonation can easily destroy them.

If by chance major engine damage is avoided, there are other serious consequences.

Diesel fuel itself acts as a lubricant for the fuel pump and delivery system as well as the valve train.

Running thin, low viscosity gasoline through a diesel fuel system would starve it for lubrication and cause those sensitive components to rub together, eventually destroying them.

Additionally, the entire fuel system will have been affected. That means the fuel pump, fuel filter and fuel injectors will likely need replacement. In the worst-case scenario, it might be cheaper to just replace the engine and components.

Good News For Newer Diesel Vehicles

Gasoline vehicle fuel filler openings became smaller in diameter beginning in the early 1980’s. This was in response to the mandatory use of unleaded fuel to protect catalytic converters and the negative effects of lead to human health. That’s why the smaller diameter gas filler nozzle fits into the larger filler opening of diesel cars.

Then in 2009, BMW launched its clean diesels in the U.S. with a “mis-fueling protection device” as standard equipment. Audi followed in 2011 with a similar device, and beginning with 2013 vehicles, Volkswagen redesigned its fuel fillers to accept only diesel fuel. Today, nearly every diesel vehicle — car or pickup — will only accept diesel fuel

But What About the Opposite: Putting Diesel Fuel in a Gasoline Engine?

Fortunately, this one is almost impossible (notice we said almost), since the larger diesel filler nuzzle won’t fit in a narrow gasoline filler neck.

But if you do manage to get diesel fuel in your gasoline tank, the engine will probably not even start, and if it does, it’ll run terribly and probably smoke like a chimney. Engine damage will most likely be minimal to none, but a thorough and expensive fuel system flush will certainly be in order.

This article was edited and updated by Larry E. Hall

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Gable, Christine & Scott. "Accidentally Fueling a Diesel with Gasoline." ThoughtCo, Apr. 12, 2017, thoughtco.com/accidentally-fueling-a-diesel-with-gasoline-85225. Gable, Christine & Scott. (2017, April 12). Accidentally Fueling a Diesel with Gasoline. Retrieved from https://www.thoughtco.com/accidentally-fueling-a-diesel-with-gasoline-85225 Gable, Christine & Scott. "Accidentally Fueling a Diesel with Gasoline." ThoughtCo. https://www.thoughtco.com/accidentally-fueling-a-diesel-with-gasoline-85225 (accessed January 23, 2018).