What to do if you put the wrong fuel in your car


This is a dead-easy mistake to make - especially if you are new to diesel. And it can cost you an arm and a leg. Worst-case scenario: you’ll be on the hook for $10,000+


Diesel engines use very precise high pressure pumps to amp up the pressure in the fuel rails to about 2000 atmospheres. This seems excessive, but the extreme pressure is needed for injector control in the millisecond domain.

Very precise cam-type fuel pumps are used. Unfortunately, they need the lubricating properties of diesel fuel to function and survive. Petrol has lots of interesting properties; lubricity is not one of them.

The hardened steel faces on the cams disintegrate, and the metal fragments travel quickly downstream where they lodge in the microscopic holes of the piezoelectric fuel injectors, destroying them, too.

This is a five-figure mistake. Everything downstream of the high-pressure pump needs to be replaced. Everything upstream, including the fuel tank, needs to be cleaned out.

My strong advice is: Don’t do that, ever. Carmakers should do a far better job warning about this danger. And, frankly there’s no reason a system could not be contrived in which it was impossible to put the square peg of a petrol nozzle into the round hole of the diesel receptacle.

As things stand, it’s up to you to get this right.

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If you become aware you have done this, before re-starting the vehicle, do not start it. Not even a bit. Not even to get it away from the pump and into a parking bay nearby. Not even if Ahh-poo gets very very angry indeed.

Conscript some cheerleaders - in the spirit of equality - to help you push the vehicle out of the way, if it’s really necessary. You’ll be getting your car towed from here.

In this case it will most likely be possible to clean out the tank and the low-pressure part of the fuel system, and the cost won’t be prohibitive. Do not start the vehicle. If you do, things will get rapidly worse.

If you have started the vehicle, and you become aware of this error, shut it down urgently. Obviously don’t stop anywhere dangerous, because it’s not worth dying for. But make getting safely shut down a real priority. Arrange a tow. You might dodge a bullet here … one never knows.

And if you’ve been greeted with deafening silence already - you’ll be getting a tow from here on in, too. And brace for impact, because it’s probably going to be expensive.

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Obviously, one place you might want to have the vehicle towed is the dealership - but they do tend to rub their hands together at this point, not to mention line up 100 industro-spec Dyson vacuums and anticipate eagerly the commencement of docking procedures with your bank account.

Nothing a dealer likes more than the sniff of desperation in the air… So you might want to have the vehicle towed home instead and spend a few hours on the phone investigating repair options near you. Specialist diesel repairers near you might be able to do the job substantially more cheaply than the dealer. Certainly, get more than one cost estimate.

It’s still going to be expensive, but there’s less likelihood you’ll need to use the onsite defibrillator with an independent workshop. But you do want a diesel specialist, because this is a technically demanding job.

I cannot stress enough the advantages of prevention over cure here. Measure twice and cutting once when it comes to re-fuelling a diesel - especially if you’re new to diesel.

And look, if you mis-fuel the other way around by putting diesel in a petrol car, it’s probably not going to be hell on earth in quite the same way - that’s a mistake that you can generally clear up for under $1000.


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