Is my Hyundai i30's fuel consumption excessive?

Hyundai i30 Premium

Hyundai i30 Premium


I purchased a new Hyundai Hyundai i30 (Premium) in April 2013. I really like the car, so much so my wife purchased another new Hyundai i30 (Elite) two months later in June 2013. Unfortunately a car ran into the back of my car with-in the first three weeks and less than 500km. It was not a big smash and the only damage was to the rear bumper. It was replaced. I had the repairs done at the Pennant Hills dealer where I bought the car.

My problem is fuel consumption. The Hyundai manual states it is OK to run the i30 on e10 fuel and the brochure states the automatic should get 9.7L /100km for urban usage. I have complained to the dealer that my consumption has been well over the stated consumption in the brochure, which I have been testing for about 14 months - full tank to full tank.

It has been as high as 14L/100km. I have had the 1000km and 12months services, and I still get the poor consumption rate. The dealer has told me to use 95 unleaded and I will get better consumption. For the last month I have been using 95 unleaded and found the consumption to be the same as before i.e. 9.9L/100km and higher.

My Hyundai i30 has now done about 16,000km and my wife’s Hyundai i30 has only done about 5000km.

The confusing thing is my wife’s Hyundai i30 get the same fuel consumption for urban usage using e10 fuel as I do using 95 unleaded and I have my Hyundai i30 set on the economical setting and she has her i30 set on standard setting.

My question is what could cause both i30s to get dissimilar fuel consumption. They both have 1.7L motors, they are of similar age and my wife uses the air conditioning a lot, where I open the roof to cool the car. Nether of us are fast (heavy footed) drivers.

The only difference seems to be, my car has had a rear-end accident. Could it be the repair and any changes to my cars muffler causing higher fuel consumption? Can you suggest any other factor that could cause different fuel consumption? I would much appreciate any advice you may be able to give.



The Hyundai i30 is a very good small car - objectively one of the best mainstream small cars in the market today. The smart money says your Hyundai i30 does not have a problem. Neither does your wife’s car. (I get this question a lot. Often, people don’t like the answer. So: brace for impact.)

The minor crash has most probably not affected, and cannot affect, the fuel economy. Servicing won’t affect the economy. (Unless your air filter is blocked from sustained dusty environment use, etc. - unlikely in such new cars.) Service is just there to ensure the car doesn’t break down. It doesn’t have a profound impact on fuel consumption. 

The ‘economy’ setting on cars is a joke and will not deliver a meaningful benefit in economy. It really just reprograms the auto transmission shift points so the car adopts a higher gear earlier.

The Dealer Has Brushed You Off

Guaranteed, your dealer is an asshole. Abrogating the alleged problem onto the fuel is a typical low-rent dealer brush-off. Premium fuel delivers a slight (immeasurable - at least with the tools you’ve got at hand) economy benefit. The increased economy on 95 or 98 is always more than offset by the increased cost, so running 95 or 98 is just blowing money out your exhaust pipe. There's no tangible benefit.

Different Fuel Types

The e10 fuel has three per cent less energy in it than 91/95/98. (Octane has nothing to do with energy density - it’s a measurement of resistance to autoignition.) Ethanol has 30 per cent less energy than petrol, litre for litre. Therefore a 10 per cent ethanol ’shandie’, which is what e10 is, has three per cent less energy than petrol. Therefore consumption goes up three per cent on e10. (So if e10 isn’t three per cent cheaper than 91, don’t buy it.)

How often do you standardise the tyre pressures? Valve cap tyre pressure monitoring isn't as good as using the same pressure gauge once a week, reinflating and checking the pressures cold.

Experimental Errors

Realistically I don’t think you’re measuring the economy any more accurately than within 10-15 per cent, so all your measurements carry this degree of error routinely. Here’s why:

  • Define ‘full tank’ - if you’re doing it to the first click or second click, you’re kidding yourself. Pumps vary widely in terms of when they click off - often in response to flow dynamic pehenomena like a bubble coming back up the pipe. You can often tip five to seven litres of additional fuel in after the first click. If you use a different pump every time, at a different servo, variation between pumps will also be a factor. The only way to do ‘full’ is stand there for another 10 minutes and trickle fuel in, until it’s right up the top of the spout. And…
  • ...and if you do that, don’t go home and park the car overnight, because as the car cools overnight the tank will shrink, and dump a few litres of fuel on the driveway, which will evaporate quietly and root your experiment.
  • So you have to fill up, then drive many kilometres, and this has to be normal driving for you - which is not how you use the car, so your experiment is not representative of how you drive. So...
  • you can’t actually measure the fuel consumption very accurately at all.


Car companies in Australia are required by law to state only the fuel consumption from the mandated and standardised tests done in the certification process. The testing process is way out of step with reality, the upshot of which is that there’s a small army of people like you who are angry their cars aren’t delivering as promised - and here the carmaker is blameless. It’s the regulators you should be upset with. There’s a full explanation of the problems with the official fuel tests in the video. 

Scientific Method

If you’re getting 9.9 out of your car you’re doing very well - that’s 24mpg in the old money - for urban running. Even 12 or 13 is OK. It doesn’t seem to me like either car has a problem. Different driving styles and different operating environments account for any observed difference, plus of course the experimental error intrinsic to your measurements noted above. Finally, and you’re probably really not going to like this, there’s the whole ‘scientific method’ thing. If you want to do science, here’s how that works: (I was an engineer - I spent, subjectively, for ever in labs.) Science is about doing a series of experiments, eliminating variables, taking measurements, objectively assessing the results and drawing conclusions. Science is not about attempting to prosecute a pre-drawn conclusion, conveniently. I think you’re trying to prosecute the argument that your car’s consumption is excessive. I don’t believe you can measure the fuel consumption accurately enough to prosecute an argument that your car is consuming fuel excessively.

A smarter way to do this is reset the trip meters on both cars, drive for several weeks, and let the computer dish up a reading. Use the same fuel in each car. Check tyre pressures every week and inflate to placard maximum. Start with a full tank, finish with a full tank, and keep records of how much fuel went in, and how far you drove in total - do a long-term average over time. Preferably three months or more.

Additionally, one big difference between the two cars: yours is heavier (because it has more standard equipment - at least one of which items is a dirty great glass roof that weighs a lot more than the tin roof on the other i30). And they run on different wheels and tyres - good luck measuring the rolling resisitance disparity there… (Rolling resistance accounts for as much as 20 per cent of all fuel consumed…)

Finally I suspect with all due respect that you’re probably not the right person to do a robust fuel consumption test here. (The cars don’t have a 1.7-litre engine, as you said. It’s a 1.8. You haven’t exactly laid out what the observed, long-term economy disparity is between you car and your wife’s car.) I doubt you’ve got the skill set to do this assessment robustly (that’s not a criticism - you just haven’t laid it out like a technocrat, and you need to be one of those to eliminate the variables so that any test you do yields meaningful results).

It’s a pointless exercise anyway. Just enjoy both cars. Trust me: There’s no problem.

Finally, on dealers: They get this question a lot. The car almost never has a problem - the complainant is almost always someone with too much spare time. (Who has time to measure fuel consumption?) They should do a better job explaining where the official fuel figures come from, and why they're not representative of real driving. 


Thank you for your reply. You have gone into far more detail than I expected, very much appreciated. I was not an engineer and I know little about the workings of a car, but I was trade teacher at TAFE for 35 years and do have a technical mind. Testing of fuel consumption was done by filling up the tank until the first click for 44 refills over just over 12 months at the same petrol pump at the same petrol station. I reset the trip meter each time then wrote down the distance traveled on each tank on the petrol receipt and dived the amount of petrol used to refill the tank by the distance I had traveled from the last refill. Then filed all the receipts. A little paranoid I suppose but I was trying to get a true overall reading. 

I have put tyre valve caps with pressure monitor indicators of the both cars to keep track of my tyre pressures. I was not aware of the different weights of the cars as it was not stated in any of my paperwork but I had noticed the wider wheels on the Premium but I didn’t take that into consideration. Stating the motor was 1.7L was a silly error, my Honda Civic for the last 10 years was 1.7L (it was a good car but when purchasing a new car I thought the new Honda Civic was crap).

Your explanation on E10 against 95 Octane was very interesting and I will take it on board. although I have heard that E10 can do bad things to the parts, tubes and pipes of the car engine, Is that true?

The real thing I wanted to fine out was the possible effect a miss fitted muffler can have on the fuel  consumption, causing some kind of back pressure? When I had the car repaired at the dealers  (thinking they would know the car and do a good job to bring it back to new as they said they would) I had to take it back four times. Once to have a bracket bar secured … they had left a bolt off which left it spinning around, twice to have the boot lid adjusted because it was unaligned, and once to have a cable connected in the bumper so the boot would open when locked with the keys in my pocket. I only found this was malfunctioning because my wife had the same car. This has lead me to the thought that the muffler may not be fitted correctly. 

And yes it is a good car and I love driving it. Thanks again for your time and advice.


I think the first click testing method is extremely variable - potentially - and would possibly contribute to wide variations between results. It is good re-filling practice, however, because of the volumetric changes with temperature and the fact that some air space in the tank is at all times desirable to allow for expansion.

The Premium i30 is the same car with higher equipment levels - in particular the glass roof, therefore it weighs more. How much more is unknown. You are right that the new Honda Civic is crap - Honda has dropped the ball since the GFC, and its sales and reputation have plummeted.

E10 will only damage some older cars, the plastics in which are not stable in ethanol. Newer cars are all robust when exposed to the ethanol. If the manufacturer says e10 is OK, it is.

Certainly a poorly fitted muffler can restrict exhaust and hurt power/consumption. I discounted that from my initial response to you as you specifically the crash caused only bumper damage. Are the rear tyres wearing evenly? If not they could be scrubbing out as a result of the floorpan being bent, which adds significantly to rolling resistance. I'd be monitoring that.

It's one thing to review is the individual results - if there is wide variation you’d have to ask why, because that points to errors in the method, or differences in the driving. You are saying your results vary from 9.9L/100km to 14L/100km - that's almost 50 per cent. Anything related to the crash would have a constant effect on consumption. Wide variations in results would prompt me to look for a lack of experimental control - different pumps, different refilling styles, different driving styles, etc.

However, if you’re averaging 10-12L/100km I’d have to say that’s fairly normal for a car like the Hyundai i30.

One final point: Dealers are the worst crash repairers of all time. A proper independent panel beater is always better.