[Morias]

I have seen a few posts which touch on this topic, but I haven't found one which directly addresses it.  My apologies if it has been discussed elsewhere.

My question is, and it is probably a simple one, why does fuel economy get better as you do more kilometres.  My guess is that it is about friction in that as the engine gets run in, everything gets looser and more lubricated, and hence you get better economy.

I only have about 300km on the clock so far, and am getting fuel economy between 6.5 and 7 litres per 100km for a diesel manual.  I am hoping as the kilometres run up, I will get the figures other people are posting here.

[murrayhewitt]

around town after i bought mine, for the first 200km i averaged 7.9 for a diesel manual.. slowly but surely got better and now, at 9400km, we just did a 1100km return trip to charlotte pass from sydney at an average of 4.1 doing around 115km/h more or less the whole way with a heap of gear and two people in the car

after my first oil change at 7500km i really noticed the difference. on this tank around town (the hills of northern sydney) we are on 4.9, and that is driving her pretty hard.

it will get better!

My question is, and it is probably a simple one, why does fuel economy get better as you do more kilometres.  My guess is that it is about friction in that as the engine gets run in, everything gets looser and more lubricated, and hence you get better economy.

I think you have it pretty much with the reduced friction although I don't think you can say that it's "more lubricated".  Lubrication is based on oil flow which will change little during the life of the motor.  Most of the friction comes from the pistons and rings "scraping" up and down the cylinders, which wear nice and smooth during the run-in period and then just "slide" easier.  Things should improve quickly at first then more slowly.  By the time you reach 15,000km you will be near the best you can get - my guess anyway.

[Doggie 1]

I was wondering about this too. I picked up my diesel manual last Wednesday afternoon, have done about 1100 kms since then and the average fuel consumption is currently on 6.4 l/100km. I am trying to run it in properly, vary the engine revs etc and not actually drive it for economy yet.
I hope it improves with age like a good wine.....

[Dazzler]

I usually have a good mix of short trips (under 10km Urban) and longer trips (50 to 100km) and with more than 30,000km on the clock average about 5.4 in Tasmania's hilly terrain.

If I have a period of just urban drive (less than 10km trips) she creeps up towards 6.0. Whereas, a good long trip and she ventures towards 5.0..

My economy hasn't changed much since I got her ...   

[Lakes]

I'm with Dazz, don't think economy improves much with age, but they seem to perform better as they get more k's up.
i was able to get 4.4L/100k tank average for a trip ( this is fill tank to very top, drove 1,200k then fill tank to very top same pump same servo and work out average fuel useage per 100k) that was when car had less than 10,000k.
then a month or so back i tried to better that average i managed 4.3L/100K this trip was 900k, motor now has 31,500 and one week to go before she turns one year old.

[2i30s]

I'm up to 950 kms and it does keep keep getting further on petrol and has got more power,i cant comment on howmany ks per liter coz my i30 is only an sx and i dont have a trip computer. 

[phuney]

I am hoping it does as my petrol SX is nearing the end of it's first full tank and has only managed 390 km's on that tank and 500 in total. At 10.4 litres per 100 km it should be nearer to 500 km's. See how it goes on it's second.

[fatboy_daveb]

Hi all

I'm in the UK and I own two i30s, and I can't say either way if adding miles makes the engine more efficient or not. I have a 2007 2 litre diesel with 24,000 (over 38,600 km) miles on the clock, and a newly acquired 1.4 litre petrol with 2,700 miles (4,345 km). The diesel started off very well and I was averaging the low to mid-50s mpg on the 300 mile motorway runs at 70mph, but after my first service at the 12,500 miles it has gradually worsened to averaging 45 mpg (6.3l/100km) on the same run. I was honestly expecting the mpg to improve as the miles piled on, but this has not been the case. It goes in for its second service this Friday so i am hoping that will sort it out (maybe the wrong oil was used the first time round?). The 1.4 petrol engine started off fairly tight and would only average about 38mpg on its first tankful. Indeed, it gave it a range of 327 miles when I first filled it up. After 2,500 miles it gave a tank range of 399 miles upon filling, and will average 46 mpg on the same 300 mile motorway run that I referred to earlier. I am curious to see if the petrol follows the same pattern as my diesel. If it doesn't, and the petrol continues improving, then I will be left in the strange situation of having a petrol engine being more efficient than a diesel.

I know that Thumper has mentioned several times that the diesels are very inefficient when it is cold,....which it always is in the UK, and I think the diesel's intercooler has a lot to do with the fuel economy problems as it takes at least 6 miles to for the engine warm up when the outside temperature is below 8c. The petrol on the other hand heats up very quickly and and is definitely more keen to revved when cold. And that was one of the reasons I bought the petrol. Its a taxi for my mother and she driven around in it by my brother. He averages 42mpg in the petrol on a 6 mile stop-start round trip, but he would only get 26 mpg in the diesel on the same trip on the same day.

Cheers
Dave

[Dazzler]

I'm in the UK and I own two i30s, and I can't say either way if adding miles makes the engine more efficient or not. I have a 2007 2 litre diesel with 24,000 (over 38,600 km) miles on the clock, and a newly acquired 1.4 litre petrol with 2,700 miles (4,345 km). The diesel started off very well and I was averaging the low to mid-50s mpg on the 300 mile motorway runs at 70mph, but after my first service at the 12,500 miles it has gradually worsened to averaging 45 mpg (6.3l/100km) on the same run. I was honestly expecting the mpg to improve as the miles piled on, but this has not been the case. It goes in for its second service this Friday so i am hoping that will sort it out (maybe the wrong oil was used the first time round?).

 

Hi Dave,

Sounds like some issue with the diesel which I hope they sort out at the next service..

[eye30]

Hi all

I'm in the UK
 The diesel started off very well and I was averaging the low to mid-50s mpg on the 300 mile motorway runs at 70mph, but after my first service at the 12,500 miles it has gradually worsened to averaging 45 mpg (6.3l/100km) on the same run. I

Hi Dave and welcome if I haven't already said so.  Where do you hail from  and which footie team do you follow.  I'm a Blue, Everton.

My diesel 1.6 shows a constant 51 to 54 MPG and I reset at each diesel fill. I only do 7 miles to work and 5 home, so it's not getting up to optimum temp which you get on your trips, long way going as I use 1 junction of the motorway.  Whereas coming home you get q's when I get to my junction so I take the A roads.

Now at my 1st service I was charged £mega bucks for oil compared to what I had used in my Accent, There is a posting covering this topic and what oil you should use.  I'll look for it and post link when/if I find it, unless someone else finds it first,  but the Question is

Did they use c3???? grade oil.

Also, the service chap ask me when I took car in if I had any running issues as they would check ECU for up dates.  I think they said they checked but didn't alter any of my setting. But they may have altered your setting on the ECU. Just a thought.

The diesel started off very well and I was averaging the low to mid-50s mpg on the 300 mile motorway runs at 70mph, but after my first service at the 12,500 miles it has gradually worsened to averaging 45 mpg (6.3l/100km) on the same run.

I was honestly expecting the mpg to improve as the miles piled on, but this has not been the case. It goes in for its second service this Friday so i am hoping that will sort it out (maybe the wrong oil was used the first time round?).

Oil viscosity can have a real effect but you said the economy "gradually worsened".  If oil related I'd have expected it to change immediately when the oil was changed.  How do you measure the consumption?  Maybe the gradual change is due to your measurement method - like taking a long term average that includes a period before the service.

Anyway, you should ask them what oil they used and whether they will use the same this time. You're paying for it - don't you want to know what you're getting for your money?