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Plastic Vs Steel Fuel Tank – What’s Best? | Auto Expert John Cadogan | Australia

Car Design

Plastic Vs Steel Fuel Tank – What’s Best? | Auto Expert John Cadogan | Australia

What’s safer – a plastic fuel tank or a steel one?

Here’s a question from Craig.

“Recent crashes on Australian roads over Christmas ended in explosions and fireballs. Are plastic fuel tanks a likely contributor to these events? A fire at Sydney Olympic Park also led to the destruction of vehicles, which exploded. Are plastic fuel tanks a likely culprit?”

We can probably all agree that it’s unacceptable to die in a fire if you survive the crash. This nightmarish scenario is quite the challenge for engineers, because cars are essentially a pyromaniac’s wet dream.

Cars are so inherently flammable that it amazes me they all don’t spontaneously conflagrate every time you drive one. Petrol – gasoline in ‘Merica – is especially willing. The pyromaniacal girl who can’t say ‘no’.

The flashpoint of petrol is minus 43 degrees C (minus 45 F). So if it’s warmer than that, petrol evaporates and forms a highly flammable mixture. All it needs is a spark – and you are (literally) toast.

There’s so much energy – about 35 million joules in every litre. So 50 litres spilled all over the road can rapidly convert to 1.75 billion joules of heat energy. You could lift a Toyota Landcruiser about 65
kilometres into the air with that. If you could find a big enough crane.

And there’s electricity everywhere in a car – there’s even an electric fuel pump submerged in the fuel tank… What could possibly go wrong?

The only protection in the pyromaniac’s paradise we call the automobile is good engineering design.

Plastic fuel tanks are made from high density polyethylene, or HDPE. Steel is cheaper, but there’s more design freedom with plastic. Plastic tanks are about 30 per cent lighter, and they generally don’t have seams, which makes them less likely to rupture in a crash. That’s a big plus.

Plastics also don’t generate sparks, and they’re a bit more flexible than steel – in the sense of springing back into shape after impact.
When a steel tank absorbs impact energy, it crumples and often bursts at the seams. The volume decreases and fuel is ejected under pressure – which is exactly what you don’t want. Because it evaporates rapidly and becomes the girl who can’t say no.

Plastic fuel tanks are very tough. (It’s hardly as if a plastic tank is a glorified Coke bottle.) It’s even a better insulator if there’s a fire beneath the vehicle. So the fuel inside the tank takes longer to heat up … but this is a ‘good news/bad news’ story.

The good news is: in an under-car fire the fuel in a plastic tank stays cooler longer. It’s is less likely to become rapidly pressurised and vent flammable vapour. The bad news: The fire will ultimately melt the tank, and then you’ll be sitting on a two-gigajoule bunsen burner, which is pretty far from ideal.

Craig mentioned fuel exploding in a fire, but liquid petrol does not really explode. It burns. If you want to be a complete pedant, the best petrol and vapour can do is to deflagrate rather than actually detonate.

Hand grenades and blocks of C4 detonate. If you see a fireball, like in Mad Max or Transformers, it’s a deflagration. They’re different things.

When a fuel tank goes up, it’s visually compelling, but it’s not a detonation. Detonations are violent explosions that deliver supersonic, high-pressure shock waves. Petrol generally cannot do that.

When a fuel tank is breached in a car crash, liquid fuel runs onto the road. It starts to evaporate. If there’s a source of ignition, like a hot turbo or catalytic converter, the vapour deflagrates and the liquid burns aggressively. There’s usually lots of black smoke – which is the signature of an oxygen-limited fire.

The thing for engineers to concentrate on is: doing everything they can to avoid breaching the tank in a crash. Because it’s never a good day when you let the girl who can’t say no out of the bottle. For this reason alone, I give plastic the win for fuel tanks – yes!
However, please don’t run out and poke your head under the car, and decide you’re in a death trap if it’s a steel tank. Detail design really matters – and both steel and plastic tanks can be designed to be quite safe.

I blame engineers for this. It’s a miracle that every car on earth is not on fire, right now. You’ve got the girl who can’t say no, plus 100 different ways to generate a spark, in bed with extreme temperatures and ridiculously high airflow. And you’re sitting on top of it. Awesome!
Arthur C Clarke summed it up nicely.

If you think we live in a world without magic – I put it to you that your car is unlikely to catch fire today – even if it’s a Ford. And if that’s not magic, I don’t know what is.

Genius, Innovator, Voice Actor, The Original Imposter, Cat Stroker. I like to step on crunchy leaves.



  1. dikkybee

    January 1, 2018 at 11:45 pm

    After reading most comments I think what everyone is missing is the obvious and the reason why driverless cars are being so widely talked about. I have driven cars for over 40 years and have never had a fuel tank rupture or die in a fiery death. STOP HAVING FUKEN ACCIDENTS AND FIX THE LACK OF DRIVER SKILL. You only have accidents when you do not abide by the law. End of story.We seem to have given up on drivers getting better so we have to make excuses for why some people are given licences when they should not be allowed to draw another breath. Seriously have a look at most bad drivers and most seem to be imports. I have been behind learner drivers being taught by a school and have seen them turn left from the right hand lane, turning without using an indicator or, and the best, they are texting while driving or making a phone call. FFS. Penalties are not enough and, I am sorry, most repeat offenders should be doing time in jail. If you cannot pay your fine then we crush your vehicle and get some money back on the scrap. In the end driver skills are shit because if no one had accidents which causes the tank to rupture then what the fuel tank is made out of is irrelevant. The safest material is having a good driver up front. End of story.

  2. james gurney

    January 2, 2018 at 12:12 am

    one thing about a plastic gas tank is that does not rust.  If you live in a snow rich country where salt is used on the roads like Canada  – a plastic gas tank is far better than a rusting steel fuel tank any day.

  3. Sashie Ramsumair

    January 2, 2018 at 12:12 am

    Ok i ask, plastic fuel tank and diesel fuel

  4. gerza71

    January 2, 2018 at 12:59 am

    These plastic petrol tanks are not new. I used to have 1980 model XD Ford Falcon sedan with a 77 liter plastic petrol tank.

  5. preste3

    January 2, 2018 at 1:03 am

    I almost had a heart attack when I realized the fuel gauge sender is completely open to fuel or vapours in a fuel tank. Not sure what makes it safe – low voltage, vapour to air ratio – but it works.

  6. Grim Fandango

    January 2, 2018 at 1:16 am

    Oh John… You are still hanging on to the Trump/Putin election collusion delusion?

    It's been over a year of intense and unbridled investigation into all aspects by a massive legal team comprised of Hillary supporters, top flight prosecutors in their own right, and not one shred of proof of any collusion whatsoever has been discovered. And you can bet if there was, it would be on the front pages of all the leftist media.

    Why not make you New Year's resolution be to admit you were wrong, and if not apologize, at least move on?

  7. Lada Riva

    January 2, 2018 at 2:49 am

    Oh russia hacking bullshit again…

  8. Graeme Savage

    January 2, 2018 at 3:17 am

    Happy New Year John… a very combustible episode, and I totally agree, ANCAP needs to make sure that it updates its' ratings for all vehicles if they change the standard. Car sales people will use whatever they can to misinform people when comparing vehicles, aiming to make their vehicle seem equivalent or better.

  9. Kev Knight

    January 2, 2018 at 6:47 am

    Happy New Year Mate. Keep up the Great Posts.

  10. Aussie Pom

    January 2, 2018 at 10:22 am

    The XD Falcon was the first car in Australia to have a plastic fuel tank and exhaustive test were carried out using huge numbers of coolant filled fuel tanks. The tanks were made by a German supplier BASF although they thought the Australians were mad in that the drop test was much harsher as was the UV protection. A US competitor tried a under vehicle fire test on a steel unvented tank. It exploded and exited the vehicle through the vehicles sunroof.

  11. ozmaniac49

    January 2, 2018 at 12:20 pm

    Great video & thanks for giving our entrusted political masters a rocket.
    Seems they have the Melbourne African Gang car-jacking under control by "taking it very seriously".
    BTW, did you manage to score a Xmas card from Troy Grant this year?

  12. flaminrota

    January 2, 2018 at 12:24 pm

    Whats safer? Getting rid of those horrible Victorians towing fucking caravans around Straya.

  13. Charles Kittler

    January 2, 2018 at 1:18 pm

    Bring back my cock Friday….👍👍

  14. Pablo Rages

    January 2, 2018 at 1:33 pm

    OMG …ur not one of these libtards that thinks Putin influenced the American election? …. Hitliary was just and asshole !

  15. Pablo Rages

    January 2, 2018 at 1:35 pm

    … and metal fuel tanks just look better !

  16. Riparian Iama

    January 2, 2018 at 5:38 pm

    If you want to see what 1400 cars on fire looks like. Take a look at the recent echo arena car park fire in Liverpool UK.

  17. craig hamilton

    January 2, 2018 at 6:37 pm

    When i play your videos my woman hates me more.

  18. FlumenSanctiViti

    January 2, 2018 at 8:11 pm

    Thank you for no French accents today! 🙂

  19. Guillaume Romain

    January 2, 2018 at 8:35 pm

    Can't wait to watch another great vid avec vous dear John! count me in. I'm totally down for the French accent! btw Happy new year to you John.All the best

  20. joe blow

    January 2, 2018 at 9:35 pm

    "Plastic Vs Steel Fuel Tank – What's Best?"

    Like you get a choice, what ever is cheapest at the time.
    Your safety for the lowest dollar, got to love car companies.

  21. TheCcponyboy

    January 2, 2018 at 9:43 pm

    To prove your point about sitting on a potential conflagration. 1400 cars destroyed in a car park with no sprinkler system. Did some maths, a teaspoon of petrol can move a car about 200 yards, at 30mph. That is energy density

  22. Dick Nixon

    January 2, 2018 at 10:42 pm

    Johnny, talk about timing, did you see this?
    They think it started with an old car.

  23. Prof. Michael O. Zeee JCD ECS

    January 3, 2018 at 12:18 am

    Absolutely agree 😉 on your thoughts about politicians…

  24. voltare2amstereo

    January 3, 2018 at 12:56 am
    Another Ford Ranger tried to help make grilled chicken

  25. Walter Burton

    January 3, 2018 at 3:15 am

    What about plastic/rubber bladders (inside of tanks)?

  26. John Loundagin

    January 3, 2018 at 6:22 am

    Of course, the biggest question on 1-2-18 isn't "Steel or Plastic", but, rather, "Whose fuel tank is biggest, and on whose desk does it sit?"

  27. Matt !

    January 3, 2018 at 8:35 am

    Literally toast?! For a man that prides himself on his command of English, this was a very large miss 🙂

  28. saauuzza

    January 3, 2018 at 9:25 am

    I will unsubscribe if there's no french accent on next video John.

  29. MrDeepseadweller

    January 3, 2018 at 9:55 am

    No glass dildo phone, no ludicrous French accent, and no tits. (Although “the girl who can’t say no” would be a great recurring character).

    Is this a portent of things to come in 2018???

  30. mactsk

    January 3, 2018 at 1:37 pm

    A PHEV (like mine) is even more a challenge, but if you have seen a tesla fire on youtube, you will know that batteries can be even worst than petrol, less energy density but way more energy bursts out in less time compared to petrol

  31. Ben Holdaway

    January 3, 2018 at 7:43 pm

    Steel rusts

  32. northern redneck life

    January 4, 2018 at 1:12 am

    Ah, so when it comes to United States President Donald Trump, all objective thinking goes out the window. You seriously believe that Putin put him in office? Haha, funny one John. You are joking, right?

  33. James Lugmeier

    January 4, 2018 at 9:18 am

    What about making the girl who can not say no , more chooosey ? , for example , diesel cars, she may say Yes, but at a later time in life ?

  34. Helen and Dave

    January 4, 2018 at 3:15 pm

    Hi John and bonjour. Love the videos and your great delivery.
    Re plastic fuel tanks, what are your thoughts on the Jeep Grand Cherokee Roman candle (model year 1992–98 Grand Cherokees and 2002–07 Liberty vehicles) with the plastic Petrol tank fitted after the axle and effectively, part of the rear crash impact zone. These have a novelty feature of rupturing and flooding the passenger area with an out of control girl who won’t say no to setting your fucking world on fire. As these have caused horrific deaths in rear end impacts. Still plastic fuel tank 100% and jeep design team just fucking nuts ? Plus keep rocking the French accent.
    Keep up the great work. Dave in the UK.

  35. Dareis Nogod

    January 4, 2018 at 5:07 pm

    Entertaining & informative, but twice as long as necessary. Keep it short and oh so sweet, please.

  36. rob graham

    January 4, 2018 at 9:08 pm

    Can't help thinking that the position of tanks under the car and between the axles might have been a bigger improvement in safety than the change to HDPE. looking at cars of days gone by; whoever thought putting the petrol tank inside the car right at the back where it would be hit in an accident was a good idea!

  37. Bas Martinius

    January 5, 2018 at 12:48 am

    Please leave the reverb to Celine Dion, John… 😉

  38. stuart Haynes

    January 5, 2018 at 1:19 am

    Your a truly funny buggar

  39. D.E.B. B

    January 5, 2018 at 5:46 am

    At 7:46 I completely lost it when he said "Russian president and Donald Trump organ grinder".

  40. Matthew Edwards

    January 5, 2018 at 12:38 pm

    I drive a 32 year old diesel Chevy.
    Blowing up is the least of my worries just behind actually arriving at my destination this century.

  41. John Doyle

    January 5, 2018 at 6:42 pm

    Well if petrol was invented today as a transport fuel it would be banned.
    I spent my entire career working on chemical sites handling highly flammable liquids, the equipment had to be designed to exacting standards, way in advance of what a petrol car could achieve, which is why petrol engined vehicles are banned from even entering most sites that handle highly flammable liquids. So are mobile phones and all electronic kit unless specially designed.
    Yes you are correct, petrol is a fast burning liquid, not an explosive, and gunpowder is also a fast burning solid , not an explosive.

  42. Rahmi Acar

    January 6, 2018 at 12:04 am

    Hydrogen peroxide LOVES ironoxide!! It's the peroxides most sexual fantasy EVER!!!!!

  43. Peter Anderson

    January 6, 2018 at 11:37 am

    Weren't Ford the pioneers of moulded plastic fuel tanks in this country with the XD Falcon back in 1979? I remember reading something years ago where they filled both a steel and plastic tank (with some liquid) and dropped them from a predetermined height. The steel tank ruptured and the plastic one bounced.There was a fire though… when they forgot to earth the filler neck and issued a recall on the early models… Great video.

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