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Quite unlikely, but what if I rent a car and forget to ask if it takes diesel or gasoline? Is it customary that it's written next to the gas tank inlet (I've only rented a car once, and this was the case).

Or is this something that is easily deduced from the car name? Any other method?

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Small hose nozzle opening PROBABLY - as per Affeter. BUT don't do it. Just don't. You will almost certainly not be provided with a diesel car unless you ask for one. Regardless - if you put petrol in a diesel car you risk major damage. Odds are you will be liable due to the agreement that you have signed. (We travelled for 4 weeks in Europe in Eurolease turbo-diesel manual Peugeot 307 - a pleasantly surprisingly good performing car). – Russell McMahon Feb 23 '14 at 5:30
@RussellMcMahon I did get diesel cars without specifically asking for one (most recently in Ireland IIRC). – Relaxed Feb 23 '14 at 21:53
@RussellMcMahon: true you have to pay extra for diesel, but it's not unusual to get free upgrade without asking, just because they don't have the cheaper car you've reserved. – vartec Feb 24 '14 at 12:45
I once found myself in that situation after reaching the petrol station. So I searched for the manual of the car and found it. It gave the following helpful information: "If your car has a diesel engine, put diesel into the tank. If your car has a petrol engine, put petrol in the tank. ". I kid you not. – gnasher729 Jan 7 at 15:56

7 Answers 7

up vote 12 down vote accepted

It's common in Europe for many cars to have a Diesel or Gasoline version.

Usually, but it is not a rule, if the model of the car has a letter D it's a Diesel car, but this is not a rule. It's not a rule as well for the car to have a letter on the model name.

Usually in Diesel cars you will find some warnings about it.

  • The rental car agent will tell you
  • Next to the gas tank a warning about the type of petrol.
  • The diameter of gasoline hose has a different size of a diesel hose. It will be hard to put the wrong hose inside the tank.
  • The label on the key could have DIESEL written on it (HERTZ does that)

enter image description here

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Naming can be misleading, e.g. Hyundai ix35 2.0 GDI ... – André Peseur Feb 23 '14 at 22:33
I know. I only wanted to point out that the advice given above can be misleading: 'if the model of the car has a letter D it's a Diesel car' – André Peseur Feb 24 '14 at 15:35
@Karlson: most Mercedes-Benz diesel cars have CDI in the version name, with notable exception of ones equipped with BlueTec (which is diesel-only technology). – vartec Feb 25 '14 at 17:37
This is incredibly misleading. You hinted at the best answer. Inside the fuel filler flap it will read "unleaded gasoline only" or "diesel only". Usually with a minimum octane rating for gas and maybe a centane rating for diesel. – draksia Jan 7 at 16:06
Note that the petrol nozzle is smaller than the diesel one. So it is easy to put petrol into a diesel car, but hard to do vice versa. you might want to rephrase this point. :) – JoErNanO Jan 7 at 17:54

In addition to the methods already mentioned:

  • Have a look at the car documents.

  • When you start your engine, or when you have driven some meters you will know it. A diesel sounds and feels differently from a gasoline car.

  • A look at the rev meter can be revealing. The "red area" starts at around 4500/5000 in diesel cars and at 6000 in gasoline cars.

  • Open the tank. Diesel and gasoline have different smells. Diesel has a typical "oily" smell.

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Did not know that about the rev meter, interesting! – Mark Mayo Feb 23 '14 at 22:59
The second point is not so true anymore and not helpful at all for someone who is not already used to drive both. – Relaxed Feb 24 '14 at 10:45
It is still true but I agree that it requires some experience with both types of engines. – André Peseur Feb 24 '14 at 12:32

It's often very difficult to put diesel fuel in a regular gasoline car by mistake, the nozzle of the fuel dispenser is typically way too big. I assume there might be some international standard behind this, at least I noticed it in several countries (but I also came across some exceptions).

Making a mistake the other way around is actually not that difficult, I have seen it happen. Diesel rental cars therefore usually have prominent signs in several places, including on the little door or cap of the fuel tank itself. I also noticed this on diesel rentals in several European countries.

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I know someone that made that mistake (putting petrol in a diesel) as he was returning the car (in Europe) and they charged him a great deal of money. – Spehro Pefhany Jan 7 at 23:48

Look at the Glowplug Indicator

Fuel combustion in Diesel engines is achieved by temperature rise due to fuel compression alone, without the need for spark plugs. This however means that a cold engine -- i.e. one that has been switched off for a while, or one used in cold weather -- might struggle to ignite at start-up. This is why diesel engines are often fitted with glowplugs. These are electronic heating devices used to preheat the engine to facilitate their ignition.

Turns out that diesel cars have a glowplug indicator which lights up when you turn on a cold engine. As you step in the car, turn the key to the "on" position, without igniting. Various indicators should light, including the glowplug one, if relevant. The glowplug indicator can therefore serve as a hint to know if your car runs on diesel, and looks like this (courtesy of Wikipedia):

glowplug indicator

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The last several Diesels I've driven (and I've had more than a few) didn't have that indicator, or if they did it only comes on in case of failure... – jwenting May 7 at 16:26
@jwenting Turn the key without igniting and look carefully at the dashboard. I drove a new diesel car last week and the indicator came on and off very fast, mainly because the weather was warm enough as to not require a long glowplug pre-heating procedure. The indicator comes on to show that the glowplugs are being heated. It probably also comes on in case of failure, but I'm not sure since I've never had this happen. – JoErNanO May 8 at 10:00

If it's a UK vehicle you can do a DVLA lookup using the car's make and registration. It will give you a short list of information about the car. About half way down is the fuel type.

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In the United States, unless you're renting a large truck, it'll be a gasoline car.

That said, virtually every vehicle in the US is marked either on the gas cap or on the filler door with the type of fuel needed, e.g. "87 octane unleaded". Additionally, there may be a note near the fuel gauge saying the same thing.

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The neck of the diesel tank is bigger than the gasoline tank.the diesel tank neck is about 24 cm while gasoline tank neck is about 21 cm.So the diesel pump nozzle will not fit into the gasoline tank neck easily.Secondly, it will be displayed on the tank head cap.

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