Car Hire Knowhow

Diesel or petrol car: How can I tell?

Diesel or petrol car: How can I tell?

In the past, diesel cars were easy to spot: you could tell by the tractor-like sound of the engine! Modern diesel engines have made it a lot harder to tell the difference.

But the two types of engine are still completely different. And you can cause serious damage by putting diesel in a petrol car, or the other way around. Aside from draining the fuel tank, a mechanic might have to clean or replace the entire fuel injection system, which can cost thousands of pounds. 

Your car’s Collision Damage Waiver certainly won’t cover the cost, so unless you’ve got some extra protection that covers ‘misfuelling’, you’ll have to foot the bill yourself.

So – how do you tell which fuel to put in?

Look for a sticker

Fuel Cap

Rental companies often put stickers in different places around the car to tell you which fuel to use.

The first place you might see a sticker is on the car key. Or it might be on the dashboard, near the fuel gauge.

No luck in either of those places? Try opening the little ‘door’ over the fuel cap to see if there’s a sticker on the inside.

If you can’t find a label anywhere, then it’s time to look for another clue.

Check the model name

Car Model Badge

There might be a clue on the back of the car itself. Often, cars that have diesel engines will have a ‘D’ in the model name. For example, the name ‘Ford Mondeo TDCi’ tells you that the car is a Turbo Diesel with Common Rail Injection… not that anyone really needs to know what common rail injection is.
Car manufacturers use a lot of model names, such as ‘TDI’, ‘HDi’, ‘GTD’, ‘dCi’, ‘JTD’ and so on. If your car has a badge like this on the back with a ‘D’, it’s likely to be a diesel car. 

See if the fuel pump will fit

If you’ve searched the entire car from bumper to bumper and still not found any clues, you may be tempted to just go ahead and fill up. What you might not know is that diesel pump nozzles are thicker than petrol ones. So putting diesel in a petrol car can be pretty difficult: if it feels like you’re really having to force a diesel nozzle into the ‘fuel neck’, it could mean the car uses petrol.
However, putting a thinner petrol nozzle into a diesel car is, sadly, very easy. And, because petrol doesn’t have any lubricating qualities (like diesel does), putting petrol into a diesel can be particularly bad for mechanical components such as the fuel pump.
Ultimately, if you’re still not sure what fuel to use, it’s best to contact the rental company – before you fill up.

What to do if you get it wrong

We all make mistakes from time to time, so don’t panic if you realise you’ve put the wrong fuel in the engine. The most important thing to remember is not to start the car, even if the impatient driver behind you is getting frustrated. Starting the engine will begin the fuel circulating – and that can do some serious damage.

Ask the fuel station staff to help you move the car out of the way safely and then contact the rental company, who will help you get back on the road.

Talking of fuel…   

You might have heard the term ‘fuel policy’, but did you know it has nothing to do with the kind of fuel a hire car takes? 

The fuel policy sets out how you’ll pay for the fuel you use during your rental. To find out more, see How to choose the right fuel policy for your rental.