Fuel for Thought

5 Things that influence fuel consumption

If you want to see a heated debate among car owners, claim an outrageous power or fuel consumption figure for your vehicle and watch as everyone in the conversation starts debating it.

There has been a renewed interest in and discussion about vehicle fuel consumption and claimed versus real-world figures. This follows recent news reports about emission testing and the fact that both emissions and fuel consumption are tested in “perfect” conditions in a laboratory.

Fuel Consumption


We all know that everyday driving is far from perfect and that means that your fuel consumption can vary wildly from a manufacturer’s claimed figures, claimed figures by other people with the same car, and even in your own car on different days.

Stephen Fischer, founder and CEO of Steves Auto Clinic, names one example of the huge possible variances in fuel consumption:

I own a Mercedes-Benz E500 that has not received any modifications, but is regularly serviced.

With a large V8 under the bonnet, one could expect that I am used to high fuel bills with an average consumption of well above 10 litres per 100 km.

Fuel for thought - 5 things that influence fuel consumption

The interesting thing is that I have averaged as low as 7.5 litres per 100 km on the open road. The conditions were perfect, with the temperatures cool and no wind to speak of. I of course made sure to keep my driving speeds well regulated, did not accelerate hard or overtake much.

Compare that to the daily commute to our head office. With a cold engine, a lot of stop and start traffic and little attention to my driving style, the fuel consumption shoots up to an average of 14.7 litres per 100 km. That is almost double the average of my best open road driving.

To further complicate matters, my knack for keeping close records of all my vehicles figures show that I average 10.8 litres per 100 km over an extended 10 000 km period.

This just goes to show that fuel consumption is highly variable and very difficult to accurately gauge over a short period.


Here are some of the reasons why fuel consumption differs:

  1. Your daily commute 

Being stuck in stop-and-start peak hour traffic every day will not only negatively affect your fuel consumption, but it will also place extra strain on your engine. You can expect a higher fuel bill in these instances.

If you have a nice open highway drive to work, or you can drive to your destination at a steady speed without many stops along the way, your engine will thank you by using far less fuel.

  1. Blame it on the weather 

Starting your car in cold weather, or driving in extreme heat, will place far greater strain on your engine that is the case when you drive in moderate temperatures.

And while we are on the topic: If you drive your car very hard while the engine is below its optimal operating temperature, it is going to guzzle a lot more fuel than it would otherwise.

  1. What’s that on your roof? 

We fit roof racks, with rooftop tents, bull bars and large roof mounted LED bars for that once a year trip to the bush. But keep in mind that many of these extras reduce your drag coefficient (the calculation of your wind resistance). This means that your car has to work a lot harder to accelerate and keep a constant speed with the extra wind drag and you will see your fuel consumption deteriorate.

Off road tyres with greater rolling resistance also fall into this category. Those all terrain tyres are great for crawling over rocks, but this counts against them in city driving, where they require the engine to work harder to accelerate and maintain speed.

  1. Tow the line 

If you tow a caravan or trailer, you will no doubt see your fuel consumption increase. One of the reasons is the extra wind resistance, especially if you tow a caravan, and the other is the extra weight that your engine has to pull.

  1. Who’s behind the wheel? 

Driving style is an important influence on fuel consumption and vehicle durability. A cut-and-thrust style where your right foot remains firmly pressed to the floor will see your fuel consumption climb through the roof.

There are many more factors that influence fuel consumption – such as engine start frequency, vehicle age, fuel quality and how well and how often your engine is serviced.

Fuel for thought - 5 things that influence fuel consumption

With this in mind, it is very difficult for a diagnostic specialist such as one of our trained dynamometer operators to immediately identify the problem and find a solution. If you are concerned about your fuel quality, carefully calculate the average fuel use over a period of regular driving and bring that along to your nearest Steves Auto Clinic.

With the help of our trained specialists and the range of engine-optimising Unichip performance chips, we can assess if you can improve your fuel consumption or, if not, how you can gain optimal power from your current fuel usage.