Green Advice: You Filled A Diesel Car With Gasoline; Now What?

Unless you’re Argonne Laboratories, putting gasoline into a diesel fueled car is a bad problem.

Maybe it was brain fade. Perhaps you rented or borrowed an unfamiliar car. Or you simply didn’t realize that nice Volkswagen or Mercedes-Benz was a new, clean-diesel car. (It also happens to particularly stupid car thieves.)

Why it’s bad for the engine

Among other reasons never to put gasoline into a diesel vehicle,
the diesel injectors are incredibly finely calibrated to vaporize the
fuel into a very precisely directed mist. The injectors require the fuel
to have a certain viscosity, and some engines need the lubricating
properties of the diesel fuel to work properly–which they won’t with
gasoline.

While certain newer diesel engines are more capable of
running for short periods on gasoline without destroying themselves, the
advice is unanimous: If there’s any substantial portion of gasoline in
the tank–that is, more than perhaps a few percent–the mixed fuel must
be drained from all components, rather than attempting to burn it.

But
accidents happen, so what should you do if you–or someone you’ve
loaned your diesel car to–fill your tank with the wrong stuff?

Don’t run it, or drive it

First, if you discover your error before restarting the car, don’t
try to run the engine. If the fuel pump hasn’t switched on, the
gasoline may be confined to the tank, which will need to be drained.
Leave it off, and call the garage.

If
the car’s engine has started, switch it off immediately. It will likely
stall within a few minutes anyway, when the contaminated fuel reaches
the fuel injection system.

The solution is simple, but it will
likely run you at least a few hundred dollars. The following components
will need to be drained and rinsed with diesel fuel by a garage:

• Fuel tank
• Fuel pump, fuel filter, fuel lines, and other plumbing
• Fuel injectors

And in certain bad cases, the injectors and other components may have to be replaced.

The
whole process can be “either something expensive or something very
expensive,” according to the cheerful Straight Dope website. Its
“science advisory board” includes a piece on gasoline-into-diesel-cars
in the middle of a longer item on the opposite question: Can I use diesel fuel in a gasoline car?

What about diesel in a gas car?

For
the record, that too can produce dire effects. They include engine
knocking (due to the lower octane rating of diesel fuel), which can
ultimately damage the engine.

The
engine’s emissions control system, which expects the byproducts of
gasoline combustion, may also overheat or permit excess unburnt
hydrocarbons to pass through the system into the air.

But while putting diesel fuel into a gasoline car can have equally dire effects, it’s less likely.

That’s
because in the United States, the nozzle for diesel fuel physically
won’t fit into the filler neck of a car that requires unleaded gasoline.

Prevention: better than cure

Some new diesel cars make it virtually impossible to fill up with gasoline. Since BMW
launched its clean-diesel 335d and X5 models in the U.S. last year,
they have all been fitted with a standard “mis-fueling protection
device.”

BMW’s
prevention device is a special mechanism in the filler neck that
requires the larger-diameter diesel nozzle to trigger a mechanism that
unlocks to open a flap to permit fueling. Hoses for unleaded gasoline
have a smaller diameter, and cannot trip the catch that operates the
device.

Audi has developed a similar system
that it will fit to its 2011 diesel models. In the States, those are
the A3 TDI compact hatchback and the Q7 TDI sport utility vehicle.

At least one similar device, known as Diesel Key Europe,
is available as an aftermarket accessory in Europe. It can be installed
by the car owner, says the company, and also has the secondary benefit
of preventing siphoning by fuel thieves.

This story originally appeared at Green Car Reports