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Don't fill your vehicle with fuel


WhiteTruckMan
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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.

WTM

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wiz-king

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And, don't fit you boom boom speakers by screwing them with long self-tappers to the floor of the boot and wonder why the car smells of petrol if you more than half fill it - young DIYer just up the road from me.

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WhiteTruckMan

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spider9

I had to think a bit about your post, and heres my take on it.

The litre expansion I spoke of refers to a car fuel tank. As has been mentioned, they are mainly plastic these days. I really dont think plastic is going to undergo any significant change over the sort of temperature ranges we are talking about.

A truck tank is a significantly larger kettle of fish though. Mainly aluminium these days, but still a significant number of steel ones about. I confess to not looking up the figures (if anyone wants to, and work the numbers to produce a meaningfull answer I'm happy to look at them, just too lazy to do so myself) but the significant factor would be the coefficient of linear expansion. Over the size of a fuel tank I think its going to be millimeters at best. However, the expansion of 600 litres of fuel (an average size, I've used truck that carry up to 1600l) over a temperature rise of 20°C (exposed to direct sunlight, remember?) gives an expansion of nearly 10 litres!

WTM

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Aitchbee

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I remember Boyle's Law from school.I think it was (in a nutshell)...if a liquid was heated up (ie Temperature increase), then the volume of that liquid would increase...Pressure was also a factor.

Anyway...why can't trucks and any other vehicles which use petrol/diesel as means of propulsion, have a little inbuilt fridge to keep everything cool.

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OTT_B

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WhiteTruckMan

Plastic fuel tanks are made from HDPE, which has a broadly similar coefficient of volumetric expansion to diesel.

That aside, and as FE and myself have already pointed out, there really should be no issue with car fuel tanks in hot weather. By way of example of why fuel blow back isn't an issue, consider this:

Diesel engines pretty much univseally run high pressure pumps now in order to get sufficiently high injection pressure. One of the side effects of this is that the pump has to pull up far more fuel than the injectors need. The excess fuel, after being heavily worked (and therefore heated up) by the fuel pump, is then returned to the tank. When it arrives back, it can be a good 50°C hotter than when it left. After a couple of hours running, the entire fuel tank temperature increases by 40°C or so (depending on a lot of factors). Yes, the tank pressure increases. But if it goes beyond a predefined limit, the vent valves open to relieve the pressure. On a long run on a hot day, the valves can be opening and closing continuously. Has anyone had a face full of diesel when stopping to refuel their Mondeo? No.

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spider9

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WTM "..would be the coefficient of linear expansion"

But a metal tank is a 3-dimensional entity, so each dimension will expand according to the linear coefficient, and so, in theory, the size of the tank shouldn't matter, anyway.

But as has been said, pressure valves mean the warning about filling your tanks doesn't really stand scrutiny. I'm also sure fuel retailers would have been warning of this if it was an actual danger to the average Joe.

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flycatcher1

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Expansion does occur in a plastic petrol can as I found out when I went to fill the mower up today.

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WhiteTruckMan

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OTT_B

2 points. I dont dispute the part about heated fuel returning to the tank etc. However, after a couple of hours running a truck will have consumed a far greater volume of fuel that could possibly be replaced by expansion. Also, the original point of this thread was about filling tanks to the brim, then leaving them parked in the hot sun all day, not running.

spider9

The pressure is almost an irrelevance. It's highly unlikely to cause damage in a car. It can and does happen with trucks, as I saw with my own eyes last week (and on other occasions over the years). However, what car owners do need to be wary of is the dangers that fuel poses when it expands and overflows through the very pressure relief valves that you have in mind. That, and the loss of very expensive fuel.

Take a look at what the fire service has to say about fuel, especially about filling up

Fire service fuel safety

WTM

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Forum Editor

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"what car owners do need to be wary of is the dangers that fuel poses when it expands and overflows through the very pressure relief valves that you have in mind. That, and the loss of very expensive fuel."

I'm not getting your point, or you didn't get mine - there isn't going to be be any overflow or loss of fuel from a car's tank. They are designed to prevent that from happening. My car has a fuel tank expansion chamber that is specifically designed to accommodate fuel expansion without any loss of fuel or vapour.

I imagine that all modern cars have the same feature.

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WhiteTruckMan

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FE

I refer you to the fire service link in my previous post, specifically where they say "do not overfill your tank and make sure that the filler cap is securely in place and not leaking. Fuel expands and vapour can build up in hot weather, so avoid filling to the brim."

Collectively they must have more practical experience of this sort of thing (and its consequences) than you or I could ever hope to gain.

WTM

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bremner

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I think the wedsite advice is generiic in respect of cars. Modern cars have expansion tanks and safety valves that prevent fuel spilling out in heat. Older cars do not and for them the advice is valid.

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