Expert advice: Running out of fuel – all you need to know

Running out of fuel

Running out of fuel at the roadside is a bad idea for many reasons. For a start it can put you in unnecessary danger, stranded beside speeding vehicles. And depending on the kind of car you drive and its age, it could cause mechanical complications when you do get fuel.

But that doesn’t stop hundreds of thousands running out of fuel every year. I read a survey a little while ago which said that 70,000 drivers a month run dry on the road. The problem seems to be that owners overestimate how far their car can travel when its tank is nearly empty. Here’s what you need to know.

How do you know your car is running dry?

The fuel gauge is designed to be the first sign that your car is running out of gas. When the fuel tank gets beyond a quarter empty an orange warning light comes on. On some cars, the range function then automatically lights up on the instrument panel.

Ignore this and as the fuel tank drains, your car may start to sound like it’s spluttering. This is a misfire which means some of the cylinders aren’t getting sufficient petrol to burn. It won’t do this for very long before it conks out altogether.

Is running out of fuel bad for a car?

The roadside is a very dangerous place to spend time. But apart from that there are a couple of reasons why it’s less than ideal to run out of fuel.

Older cars can have debris that’s accumulated over the years at the bottom of the fuel tank. There are filters designed to prevent this making it into the engine. It’s better those don’t get clogged as eventually this may impede the flow of fuel.

The fuel also cools the fuel pump. But don’t worry, running out of fuel once shouldn’t damage the pump. Running out multiple times might. Of more concern is that you may struggle to re-start your car.

How easy is it to re-start a car that’s run out?

Running out of fuel

Ideally you don’t want to be doing this… (Picture istock/stockyimages)

This really does depend on the car. The fuel system will have got air in it when the tank runs dry. Once the tank has fuel in it again, when you turn the ignition on, the fuel system should be primed and ready to start. Turning over the engine should then purge the air. The engine might take a bit longer than usual to fire but it should start without any problems.

On older pre-fuel injection cars it could be tricky to re-start, particularly if the carburettor had run dry. And some older diesel cars needed to have air bled from the fuel system after they’d run out of fuel.

Do you use the range computer?

Ever played fuel station roulette? That’s when you use the ‘range’ function on the car’s trip computer to gauge how many miles are left in the tank. To do this with any certainty relies on the car being able to calculate the range accurately. But how do you know that’s what it’s doing?

I’ve read tests of car trip computers where it’s been found they’re on average around 5 per cent inaccurate. And we’ve been called out to cars that have conked out through lack of fuel, despite the computer saying they’ve got a range of 40 or so miles left in them.

Equally, some cars err on the side of caution, saying the car has zero miles left in the tank when they’ve actually got another gallon. The message is: you can’t rely on a car’s computer to be accurate. As soon as the low fuel light comes on, find a service station.

Is it illegal to run out of fuel?

It might be careless but it’s not illegal to run dry. In fact, the law cites it as one of the reasons you’re allowed to use the motorway hard shoulder. That said there have been cases where drivers have been fined £100 and given three penalty points for careless driving if they’ve needlessly run out, leaving their car in a dangerous position. And in some countries such as Germany it is illegal. The overall message is, it’s much easier NOT to run out in the first place.

motorway hard shoulderNick Reid is head of automotive technology for Green Flag and is a fellow of the Institute of the Motor Industry

14 comments on “Expert advice: Running out of fuel – all you need to know

  1. Mr Barry W Linnard 26/06/2018 7:55 AM

    Putting diesel in a petrol car can be equally disastrous.
    I did this in a B M W and started the car before I realised. Called RAC who said no problem just fill up with petrol. The small amount if diesel will do no harm “just like a shot of Redex”.. The result was that the oil in the diesel left a film on the cylinder walls. This caused a “hydraulic” effect which lifted the cylinder head. So 2 lessons. 1.Dont put diesel in a petrol car and 2. don’t believe what the RAC tell you!

    • RICHARD 26/06/2018 9:20 AM

      To me that’s a bit of a tall story and I think the RAC’s advise was correct.

      What you don’t say is how much diesel you put in your car? If you almost filled it then no amount of top up petrol will balance the mix. On the other hand, if you only put in a 1/2 gallon and assuming you could top that off with a healthy dollop of petrol then it should cause no harm. Also keep in mind that the fuel line will still be full of petrol so no neat diesel would get to the engine, it would of course eventually draw in the diesel/petrol mix which would be fine, it might smoke slightly but that’s about it. I also don’t get the ‘hydraulic’ lock comments. Hydraulic lock only occurs when the cylinders are full of water, oil or fuel, Film on the cylinder walls – really!

      Finally, cylinder heads don’t lift due to wrong fueling, if this were true then diesel engines would fail to operate. Sorry Barry, I don’t believe any of this story but I might change my comments if you had put a significant amount of diesel in the tank. If this were so then I dare say you mentioned this to the RAC operative otherwise his advise would have been to drain the tank.

    • Gordon Carey 10/09/2018 8:09 AM

      Rubbish. The diesel did not cause your problem. The same with petrol in a diesel; only up to 3% though of the total fuel held in the tank.

  2. Ray Stevens 26/06/2018 10:04 AM

    i never allow my car to go below quarter of a tank, as soon as it reaches that mark its time to head into a garage and fill up, thats a lot safer than running out of fuel and risking what ever, my son recently had bought a brand new car, his first car sadly by the side of the motorway changing a wheel front offside which had blown up he was hit by a car traveling in excess of 60mph and end result one broken leg with severe damage…. motto, check fuel, check tyres every time you go out because the end result could be far worse

  3. Carrosserie 27/06/2018 2:23 PM

    Very informative article for those who are not aware of such situations! Thanks for sharing.

    • Mr Barry W Linnard 27/06/2018 2:29 PM

      BMW told me that the tolerance between the piston rings and the cylinder walls is much finer in their engines than many other engines. Maybe you could get away with it in an old ford escort!

      • RICHARD 27/06/2018 5:40 PM

        A hate to disappoint you Barry but BMW engines are no better than any other manufacturer.. We have a BMW Mini Cooper S and that’s got a Peugeot engine in it. Garages just love to tell you things they think you want to hear, I had a tattered Ford Escort back in the day, I thrashed it everywhere and it never broke down…

      • Peter Martin 05/09/2018 11:10 PM

        That’s utter nonsense, BMWs are famous for burning oil these days as their engine tolerances are obscene and amongst the most troublesome available. Just research the N47 /N57 range of engines whose timing chains regularly let go or the M3 V8s whose crankshafts fail. That’s why all German cars are now done of worst in reliability tables

  4. Ken Miles 05/09/2018 8:16 PM

    Very informative, thanks

  5. karen walker 08/04/2019 7:53 PM

    I see in the photograph he is using a plastic container, I was told by a friend these were not legal as very dangerous if there is a fire in a crash, I was told the metaal Jerry Cans were the only ones allowed, is this true?

  6. Colin Robinson 10/04/2019 6:58 AM

    An issue today seems to be cheap petrol, and its additives, if left for a reasonable amount of time the additives tend to both cause some sticktion (stickiness in parts such as injectors ,pumps, and lift pumps) the advice given was to run the tank to quarter full and fill up with fresh fuel if you do not use a lot of fuel or leave the car standing for long periods of time, If you are a high mileage driver it would not really affect you.

  7. Gordon 12/04/2019 6:56 AM

    I think car manufacturers should give ‘accurate’ petrol consumption of their cars rather than the ‘selling’ consumption.
    Also my car has a average mpg display but I find when I actually check the consumption on a fill up it is less than that displayed.

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