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Why you shouldn’t let your fuel tank run down too low

Filling up at Mt Dare, squeezing in every drop possible before doing the Madigan Line.
Filling up at Mt Dare, squeezing in every drop possible before doing the Madigan Line.

Did you just drive past that servo, and then nervously stare at your fuel gauge? I do it all the time, with that internal dialogue always happening: “She’ll be right, I’ll make to the end of the highway before needing more”.

And then, moments later: “Oh, man. It’s going down so quickly. This fuel gauge is a goddamn liar”.

But the important fact is: I shouldn’t do this. And neither should you. Here is why you shouldn’t run your fuel tank down.

Fuel cools and lubricates the pump

This is the main reason, beyond any other. Running a fuel pump without fuel is like running an engine without coolant and oil. It’s a systematically bad idea. If you want your pump to live a long, ensure it’s always well submerged in fuel: The fuel actually cools the electric pump as it passes through, like coolant in your engine. It also lubricates the pump, reducing wear and tear significantly.

Good, versus better. Good range is always a bonus in a touring 4WD, and the best way to do it is with a long range tank.
Good, versus better. A good range is always a bonus in a touring 4WD, and the best way to do it is with a long-range tank.

You might pick up some extra crud

When you’re fuel level runs low, your fuel is going to be sloshing around a bit more and splashing as you go around corners. What you’re doing is aggravating any crud or particles sitting in your tank, which will no-doubt be there on any vehicle with a few kays on the clock.

Air in your fuel system is bad

This goes without saying, obviously. Fuel tank and pump designs are made to keep the pump sucking down only the finest in fuels, without any air getting in there. But in the real world, it doesn’t always work out that way. Keep the air, by keeping a decent amount of fuel in the tank.

Only very old vehicles will have an inline pump or lift pump somewhere other than in the tank, just about every 4WD in recent memory will have an in-tank pump. The problem is that the pump might be really hard to access. Do you have to drop the tank completely to access the pump, or is there an access hole somewhere in the car? If you’ve got accessories like drawers or a fridge in the back, it’s worth checking if these get in the way.

Madigan Line Simpson Desert Trip 2015
“…You have how many jerry cans?”

measuring your mileage

Want to figure out how much you’re getting from a tank? Don’t try and get every last metre before fuelling up; There’s a better way of going about it. What I do is fill up my car, either to the first click, or when I can physically see the fuel in the filler. This way, I know exactly how full the tank is. Reset your odometer, and drive off. Then, when your 4WD is somewhere between 1/2 and a 1/4 full, do the same thing.

But, instead of saying ‘I get XXX kms to my tank’, see how many litres it took to refill the tank to the same level. Then, you can accurately calculate your litres per hundred kilometres, or kilometres per litre, or furlongs per flagon, or whatever.

Want to learn more about the basics of a fuel pump? Check out this video we saw on Youtube:

 

9 Comments

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  • Well on x trail the fuel gauge is dogie when down past halfway and when i put the key and switch it on the gauge don’t registers and the lights on i switch it off then switch it on the fuel gauge goes back to near half way what a bugger lucky i know its falts and bye the way it goes better than my v 8 11 klm per litre the 8 7 kpl

  • I regularly run my 200 and 125 litre fuel tanks very close to empty ( No in-tank pump). I know that once the fuel light comes on, I have another 100 kms to find myself a service station. As is with most cars.
    There is a lot of crud that floats on top of your fuel. i.e. wax from winter mix fuel. And you don’t want that to accumulate for too long only to be sucked in when you have to go that little bit further. I run small inline fuel filters to catch the crud ( and wax once ) from the insides of the tank. Toyota had a mates Prado for 3 days only to find it had a gut full of fuel wax in the system. Cost him nearly $1,000.
    My rig, Isuzu nps 300, weights 5 ton, yet I average 20 litres / 100 highway and desert driving. 14-15 litres / 100 around town.

  • Since reading this article I will never run my tank lower than 1/4 from now on.I didn’t realize
    that the fuel cools parts down and leftover fuel goes back to the tanks and gets re-used.

  • It is not just in-tank submersible pumps that are affected.
    Common rail and distributor type pumps also use fuel for cooling. If you have ever disconnected the fuel return line and run it into a container, you would be amazed at the amount of fuel that gets run through the pump and returned to the tank…..
    The more fuel you have in your tank, the better the cooling capacity.
    Run your tank down to the last few litres and that fuel is going to get hot, increasing wear and tear on your pump.
    I never run my tank below 1/4 for this reason. Better safe than sorry…..

  • I had a near calamity in my Disco 5cyl. a few years ago, taking my brother and partner on an outback tour.
    We stayed overnight at Camooweal and headed off to Mt.Isa, I looked at the fuel gauge, should be fine, except I did not allow the fact that I had a rented campervan in tow.
    About halfway on came the low fuel light ! Hmmm. slowed a bit to 95-100, and made it to Mt. Isa.
    Could not find a Fuel station till in the town, then I could not fill the tank as fuel was frothing up all the time, blamed the fuel, not knowing that the excess fuel had heated the tanked fuel and not liking to mix !
    lesson learned !

  • Also consistently keeping low fuel levels with diesels will result in microbial contamination thus causing bad fuel burn leading to soot, damaged DPFs & blocked EGR valves etc etc.

  • Running low on fuel is not a smart thing when offroad as the pickup may be uncovered even with a quarter tank still on the gauge. Bit sceptical about wax floating on top of the fuel. Unless the fuel has been cooled to the “cloud point” there will be no solid wax. Even then it will manifest as a fine haze of wax crystals which clog up the filter and starve the engine typically after sitting overnight.

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