Sudden Increase in fuel consumption mk3 Megane

CIP4 · 08-05-2016 08:11PM #1

I have a mk3 2011 Renault Megane 1.5dci. I've had it a year and always track the fuel consumption on fuelly from day one it averages 48 mpg but last summer was doing closer to 50 mpg. The worst it done every was in the last few months 46 mpg and that was extreme cold weather.

My last tank 38 mpg which is completely out it never done anything even near as bad as that. It was a very average trip Kilkenny to cork the car does it over and over all the time so it was very representative of the average. By the looks of things this means something is wrong to cause the sudden spike in fuel consumption. Even on the trip up and back I could notice it was harder than usual.

A few things to note:

- I calculated it correctly and always use the brim method.

- I always fill in the same petrol station since the start.

- the car drives fine like normal no warning light no noises or anything like that.

- I checked the fuel lines and can't spot any leaks also the alloys / brakes are not particularly hot so it's unlikely it's a sticky calliper all 4 tyre pressures normal.

I realise if it persists I need to get it to a mechanic but anyone any ideas ? I am going to cork on the same trip Tuesday so that should confirm it if the high fuel consumption remains.

visual · 08-05-2016 08:16PM

5 or 6 speed and do you cruise at 120 ish

CIP4 · 08-05-2016 08:18PM

visual wrote: »

5 or 6 speed and do you cruise at 120 ish

5 speed at 120kmh but I've done that journey 30 plus times and it averages 48mpg so it's not the way I am driving it or the journey itself.

Toyotafanboi · 08-05-2016 08:19PM

Yeah, are you keeping cruising speed the same?

Different animal altogether but if I cruise at 100km/h the Celica will do 43-44mpg across a tank, but if I cruise at 120 i'm looking at 35-36...

frozenfrozen · 08-05-2016 08:22PM

are the tyres wearing predictably / equally?

CIP4 · 08-05-2016 08:22PM

Toyotafanboi wrote: »

Yeah, are you keeping cruising speed the same?

Different animal altogether but if I cruise at 100km/h the Celica will do 43-44mpg across a tank, but if I cruise at 120 i'm looking at 35-36...

I set the cruise control at 120kmh for the whole motorway journey. But I do this journey several times a month always set at the same speed. It didn't just drop 10 mpg for no reason it consistently does 48 mpg on that journey. Same driving same condition same speed sudden drop of mpg indicates there is something wrong.

CIP4 · 08-05-2016 08:23PM

frozenfrozen wrote: »

are the tyres wearing predictably / equally?

Yep wearing completely even on the front so tracking is ok and I haven't changed the tyres so not that.

Toyotafanboi · 08-05-2016 08:27PM

And is the drop in mpg consistent or is it just one bad run so far?

I track every single fuel up too, via the brim method and every so often I get a tank that is fairly out of line with my expectations.

Usually I fill the car pretty much until it is spilling down the paint. Sometimes, depending where I fill up, the pump might click out a bit sooner and I may not fill the whole way up the filler neck, for example. That difference of 3-4 missing liters makes a tasty difference to your mpg figure.

Are you sure the tank was properly brimmed and didn't click off a bit too early. If it persists across a few tanks, i'd start to worry.

CIP4 · 08-05-2016 08:32PM

I brim it to the same extent everytime first click then put in about another litre. I'll fill it again Tuesday and see what the same trip again returns. It just feels too extreme like 46 mpg was the absolute worst before over 1 years worth of fills you can see it in the trip computer average consumption it's reading a lot higher than normal.

CIP4 · 08-05-2016 09:41PM

Sitec wrote: »

I had the same problem in a Passat TDI and it was a boost leak. The bottom intercooler pipe had a small hole. No EML or strange noises, eventually the pipe burst and I could hear the whistle.

It had a leak at the throttle body a few weeks ago but that's been fixed and didn't cause too much of a negative impact on mpg anyway. I'll see Tuesday if it's still bad I'll get a mechanic to look at it could do with a few bits being done anyway. Could well be something like a leak.

Ded_Zebra · 09-05-2016 12:38AM

Warmer weather so it could just be that the A/C compressor is running more. Would't be overly concerned if it is just one tank. See how the next few tanks go.

Sudden Increase in fuel consumption mk3 Megane

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