How to accurately work out your fuel economy

How many times have you had someone say to you their 4WD is only getting 500km out of a tank of fuel? What does that mean to you? How big is the fuel tank, and how far are they running it down? What size engine, tyres, and driving habits do they have?

Were they doing 90km/h on flat ground, or sitting on 110km/h up and down hills on cruise control? Fuel economy varies wildly depending on where and how you are driving. You can easily monitor your fuel economy every time you fill up; it takes a few seconds to do!

It is very useful to keep an eye on your fuel economy, as you can plan your fuel stops for future 4WD trips, ensure the vehicle is running as it should and understand how different conditions can change your fuel consumption. When you are paying up to $3.00 a litre for diesel in some remote parts of the Kimberley, you want to be on the ball with how far you can drive before needing to refill!

Want to know how to work out fuel consumption? We explain it all very simply below:

4WD fuel economy
No matter what you pay for fuel, its worth knowing your economy

Is your speedometer correct?

The first thing you should really do is ensure that your speedometer is correct. If you have changed tyre sizes, there’s a good chance it won’t be! If your speedo is not correct, your trip meter won’t be either.

You can do this one of two ways; drive along with a GPS at 100km on the speedometer and see what the GPS says (less accurate), or drive 100km on the vehicles trip meter, and see how many km you have done according to the GPS.

There will be a difference if you have changed tyre sizes as the bigger the tyre the less revolutions per kilometer it will do, compared to the original tyres on the vehicle. This puts your speedo out. For people that have gone from 265’s to 285’s (or 31’s to 33’s) your speedo is usually out by 5 – 10%. Fitting bigger tyres to your 4WD usually results in worse fuel economy. How much, is dependant on many factors; see the link for more information.

For our 80 series, 100km on the trip meter is actually about 105km – its out by 5% due to the larger diameter tyres.

Once you understand the difference in your speedo, you can work your fuel economy out every time you fill up. Simply remember to add 5% of your trip meter to the reading, and you can get an accurate economy figure.

Whilst there’s no tyre size fuel consumption calculator, you can factor it in when you work out your fuel economy by adding in the size difference. If your vehicle has gone up a tyre size by 7%, multiply your kilometres done by 1.07.

Speedometer correction
Bigger tyres put your speedometer out

Working out your fuel economy

The easiest way to work out your fuel economy is done when you fill up at a service station. Fill the tank all the way, until the nozzle clicks. Once you’ve paid, get back in your car (move out the way!) and reset the trip meter. From there, drive your vehicle around until you want to fill it up again.

When you put more fuel in, fill it up again until it clicks, and take note of the number of km you have done on your trip meter.

If you haven’t changed your tyre size, you can skip the trip meter correction step. If you have changed your tyre size, remember to factor in the extra km you have actually travelled due to the tyres. To get a litres per 100km calculator, simply do the below:

An example

Lets say we put 98.5L of diesel in our 80 series, and we’ve done 653.8km on the trip meter. We know the trip meter is out by 5%, so we multiply 653.8km by 1.05.

This gives us a correct reading (after factoring in the tyres) of 686.49km.

From there, simply divide the amount of fuel you’ve used (98.5L) by the number of km (686.49). The result needs to be multiplied by 100. This gives you an accurate fuel economy reading of 14.35 litres of diesel per 100km.

KM done on trip meter when filling up = 653.8

653.8 x 1.05 = 686.49km done on 98.5L of diesel.

(98.5/686.49) x 100 = 14.35 litres of diesel per 100km.

We use our GPS to double check kilometres travelled

Using an app

You can use a number of different apps which work out your fuel economy and record it for you (Fuelly, Road Trip etc), but remember these won’t work out your tyre diameter changes, which makes big difference.

Don’t rely on your cars computer to tell you

A lot of modern 4WD’s will tell you the average fuel consumption, and estimate the number of km’s you have left in the tank. This is handy, but not always very accurate. This is especially the case if you have changed your tyre sizes, as the vehicles computer works off a certain number of revolutions of the tyre per kilometer, and you’ve just changed that by fitting bigger tyres to your 4WD.

When will you use more fuel in your 4WD?

4WD’s are not small, or light weight, and they do tend to use their fair bit of fuel. However, you will use a lot more fuel by doing the following: 10 ways to destroy your 4WD’s fuel economy.

Driving in soft sand

Soft sand is usually where you will go through the most fuel. This is where your vehicle is working the hardest to maintain momentum, and as a result uses more fuel. For petrol vehicles, you can use up to 50% more fuel, and diesels usually around 30% more (but this does depend on your vehicle!). My record in the 80 Series Land Cruiser was around 35L/100km down at Yeagarup!

Fuel consumption on sand
Sand driving will chew the fuel

Driving at 110km/h

The difference between doing 90km/h and 100km/h is huge on your fuel economy (usually a litre or 2 per hundred km). Going from 100km/h to 110km/h is substantially more. Often this is in the realms of 1 – 2 litres per 100km too; if you have the time you can save a huge amount of money by slowing down!

Accelerating rapidly

Your driving habits play a big role in your fuel economy too. If you are accelerating quickly, braking hard and changing throttle positions rapidly you will use more fuel!

Running under inflated tyres

Your tyre pressures are critical to good fuel economy. The more you inflate them the better your economy will be. However, if you run them too hard you will have very little traction and risk having an accident. For most 4WD’s tyre pressures in between 30 and 45PSI is appropriate.

22R dual cab hilux
Under unflated tyres causes excessive fuel consumption

Towing a trailer

The moment you tow something, your vehicle has to work harder. Sometimes this is made worse by wind drag, but in majority of cases its just the fact that you are dragging a weight behind your vehicle. If you are looking for a good towing guide, check this out – A simple towing guide to keep your 4WD and trailer legal.

Roof racks, bigger tyres, different tread patterns and more weight

Anything that makes your vehicle work harder is going to make your fuel economy worse. by adding things to the vehicle that decrease its aerodynamics (like bar work, roof racks etc) your engine has to work harder to push the vehicle along.

Big Caravan
This is going to hurt your fuel economy!

If you change to a more aggressive tyre pattern, the airflow around the tyre is disrupted, and you will notice a higher consumption.

The same goes for adding more weight to your vehicle; if you put a 50kg backpack on yourself you will use a lot more energy to move around too!

Bigger tyres will make your 4WD use more fuel, as it has to work harder to turn the tyres. Even if your RPM drops at a given speed, your 4WD still has to work harder!

Sensors and other electrical/mechanical issues

For many modern vehicles, having a sensor (like the MAF) slightly dirty will send your fuel economy through the roof. These control the way the engine behaves, and if they aren’t in pristine condition you can expect poor fuel economy. The same goes for Exhaust gas recirculation systems, which tend to cake your engine up with build up. Fuel and air filters are another common cause of high fuel consumption too.

There’s a range of other things that will affect your fuel economy, but if you take the time to work it out every time you fill up, you will get an idea for yourself!

Our 80 series 1HDT fuel economy

Our turbo diesel 80 series is not the most fuel efficient 4WD on the market. It’s nearly 26 years old, and has done 374,000km. We knew this when we bought it, and have been extremely happy with it.

For general driving around town and taking it easy our 80 gets around 14.5 – 15L/100km.

If we are travelling at the speed limit on longer trips with some gear in the back it seems to go up to around 16L/100km, and on our 9000km trip to the Kimberley we averaged 16.7L/100km. This included a fair bit of 4WDing, sitting at 110km/h where allowed and not really taking it too easy.

For a vehicle that weighs quite a bit, has bigger tyres, almost every accessory under the sun and is 26 years old, we are extremely happy with it.

4WDing Australia 80 series
Filling up with fuel in our 80 Series

What fuel economy do you get?

What sort of fuel economy you get in your 4WD? Let us know a bit about it, and how often you check your fuel economy! Remember, no porkies!

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  1. Hey Brendon,

    Fair comments. Anyone doing under the speed limit should be considerate of others behind, and we have really liked the signs around Brisbane, that state ‘let overtaking vehicles passed’

    You aren’t wrong about the motor sizes either, and I’ve noticed this with our 80 Series Land Cruiser that didn’t change much whether you were towing or not.

    All the best!

  2. great article. I just have 2 points to address. if you cannot afford the fuel economy of a 4×4 and need to travel at 90 you need to also be considerate of trucks. if you drop a truck back to 90 you may loose them on the hills but they will catch up again on the flats. pull up let em pass and everyone is happy.

    2nd I drive a duramax diesel 2013 silverado and I get around 14-15 litres per 100kms that’s a 4.5 tonne car with a v8 engine. driving an under powered car with a heavy ish load will burn WAY more then driving a big powerful car at the same weights because the engine has the power. I’ve seen this misconception thrown around everywhere that a tiny engine will be more efficient when towing then a big thumper.

    to prove this I tow a 2 tonne fertiliser elevator around regularly. towing this nearly halves the fuel economy of the little old rodeo that tows it. my silverado jumps from a measly 14Litres per 100 to a whopping 15.5L per 100kms.

    I digress. as leisure drivers we need to clear the way for those whose work place is the road.

  3. Hey Susan,

    I’d be doing what you can to get compliant – overweight is still overweight, regardless of how much.

    I’m sure a lot of people don’t use their vans off road, but some do. My folks have pushed theirs as far as it will go!

    All the best

  4. Susan dickeson says:

    Yes, I can’t seem to get rid of the extra 50 kg, but I figure that with the really overweight vans out there, my infraction is minor. It is amazing how heavy off road vans are, to make them stronger they are heavier. I have asked any who have these vans where they take them, majority stay on the black top. Why pay the extra and all that extra weight? Just in case?, and they look better?

  5. Hey Susan,

    Sounds like you’ve got it sussed! Is your van slightly over weight still?

    Enjoy your trip!

  6. Susan dickeson says:

    Doing a 14 week trip up the center, then Hwy #1 to Townsville. 2011 Prado (GVM 3000, GCM 5500), towing a 2008 Supreme Getaway (ATM 1850). I have stripped out and only repacked essentials in car and caravan, I spare each, no water in caravan tank, no stone guard. Caravan weighed in at 1920kg, but my GCM is 4700kg. Some serious off road travel. Ave Hwy speed 80 – 85. Ave fuel over all roads is 14L/100km. Slow down and save fuel. Also helps that Prado has 150L tank, goes further to chose locations with lower prices.

  7. Hey Brendan,

    Thanks! Yep, there’s a big difference between 90 – 100 and 110km/h. If you aren’t in a rush, 90km is a good speed.

    All the best

  8. Enjoy reading your articles!
    We definitely added 2 litres/100km at 110km/hr for our Nissan Patrol GU 2012 using the cruise control. Whenever possible, driving at 90km/hr sounds like the way to go. Cheers.

  9. Peter Korbing says:

    Gerat site looking forward to hear more.
    Best regards.