Don't fill your vehicle with fuel

  WhiteTruckMan 09:24 26 May 2012

Might be a bit late, but with the hot weather we are having, I thought I would tell people not to fill their cars to the brim with fuel. This warning is prompted by last nights site of a night trunker coming in to work, checking the fuel cap on his tractor and getting showered in diesel. The last time he finished, he filled up for the next driver (as is normal), parked up and went home. By an odd set of circumstances, his vehicle wasnt used yesterday, so his fuel tank was in the hot sun all day, heating up and pressurising the tank as the fuel expands. And 600 litres produces a lot of expansion. such that when he checked his cap it came showering out. On him.

The obvious lesson here is that if you do this with your car, then although you probably wont get showered, cars have plastic tanks and fillers, so the chances of a rupture are that much greater. And in this heat thats a lot of dangerous fumes for the unwary. (diesel is safer as I think its flashpoint, the temperature at which it starts to give off flammable vapours, is around 60 degrees, from memory). Plus fuel is too expensive to waste.

So if you simply have to top it off, please do it just at the start of a long journey.


  Quickbeam 10:07 26 May 2012

If you fill your car to the first click out on the pump, there's enough expansion space left for no worries filling.

Trucks get filled to the very brim by drivers as a matter of course through a 4" diameter open cap at the highest part of the tank with no expansion space above giving the problem that WTM got.

  WhiteTruckMan 10:15 26 May 2012


I'd like to point out that it wasnt a problem I had, it was a problem I witnessed.


  OTT_B 11:47 26 May 2012

Fair advice, better to be safe than sorry, as the saying goes.

I'm not sure about truck tanks, but car tanks are fitted with pressure relief valves (usually two, sometimes 3 or more), which prevent any fuel from coming out in the way that you've described.

  OTT_B 11:56 26 May 2012

Sorry, posted too soon!

"cars have plastic tanks and fillers, so the chances of a rupture are that much greater."

The HDPE used in car tanks is almighty strong stuff - even the single layer tanks. No amount of heating from the sun would cause a rupture (assuming the tank isn't cracked!). It's debatable that plastic tanks are safer than the steel tanks (which are still sued on many cars). Plastic allows for some deformation when heated in a way that steel don't. It's a theoretical argument though.

It's also worth noting that one of the legal sign off tests for a fuel tank is to start a fire underneath the tank. There is a minimum time requirement before the tank is allowed to leak - several minutes of fire burning directly onto the tank.

  spuds 11:58 26 May 2012

I seem to recall the days when I witnessed a number of 'leaking petrol incidents' in warm weather. The vehicles mostly effected were the smaller vehicles like mini's. A usual remedy used by the fire services, was to mount the two side wheels on the petrol filler side, on a pavement area or similar higher ground, before taking further action.

  WhiteTruckMan 12:04 26 May 2012

The fuel tanks on trucks are usually of steel or aluminium construction. I have seen them made of plastic, but they are pretty rare and seem confined to smaller trucks, and auxilliary tanks for red diesel to power ancilliarly equipment such as refridgeration motors. Pressure imbalance is usually dealt with by the caps, which maily let air into the tank to replace the volume of fuel burned off during driving. If this didnt happen then a vacuum would be created in the tank resulting in the engine running unevenly and eventually stopping as the pump would be unable to draw more fuel. (In theory the tank itself could collapse under air pressure, but in practice a fuel pump isnt powerful enough to create that much vacuum).

Caps also (should) handle excess pressure too. But a trucks fuel cap can lead a harsh life, with daily use, and often being dropped etc. In my time I have seen some pretty bashed about caps, although they still performed their main function which is to prevent the escape of fuel.


  spuds 12:16 26 May 2012

Perhaps going on the point just raised by WTM. Make sure that you have or buy the right cap for the vehicle, because caps are designed with that vehicle in mind.

We used a 'wrong' cap once, and the fuel tank eventually 'crumpled' and leaked.

  bremner 12:37 26 May 2012

I remember reading in a car magazine that modern cars have fuel tanks that have built in expansion capability.

e.g. The tank will stop refuelling when it has 70 litres of fuel. The tank actually has a capacity of 80 litres to enable expansion.

  SB23 15:45 26 May 2012

I have always told the wife not to fill up in this weather, mainly because I know she ignores the clicks of the pump, which I have said she shouldn't. Guess what, today 15 mins before she has to go to work, she informs me that something is dripping from her car, as I'm wiping, more is clearly coming off the tank and from somewhere, and yes,it is petrol, and yes she "topped the tank up yesterday", as if I hadn't worked that one out. I'm going to look later, and typically she'll want it fixed in 5 mins, lol!

  namtas 22:59 26 May 2012

I have experienced the opposite in a car where a vacuum is created in the tank after using a near full tank. With regards to the opposite, every tractor fuel tank that I have seen has, been side mounted in the open and likely to be exposed to direct sunlight, whereas cars and light vans are usually under the vehicle and shaded.

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