Should I be concerned - falling MPG

[pinkpanther]

My Yeti is just over 3 years old now and has covered ~61k miles. I've tracked all my fuel use on Fuelly and noticed there is a downwards trend across all (122) fuel ups - see below:

 

The car had "the fix" around 10K miles ago, but was then remapped (stage 1) by Shark.

 

The VAG DPF app tells me my DPF is healthy and it regenerates every 180 - 300 miles, dependent upon use.

 

The car drives fine and according to the Torque Pro app is generating 177 BHP, which is around the expected level for a stage 1 mapped 140 BHP TDi.

 

I don't have VCDS, but Carista tells me there are no issues.

 

The car has a full service history and underwent a full service (all filters / oil / Haldex fluid) around 5k miles ago.

 

The car has generally averaged in the low 40's MPG,  but if the current trend continues I'll soon be into the 30's! 

 

Should I be concerned?

[Gyp]

The trend appears to be upwards until the 49th fill up, then slightly slightly improving followed by a slip downhill to the 87th and then it jumps about a bit.

 

Do those points align with the fix and remap?

 

Knowing you've had those things done, I'd guess...

 

Ran in and drove normally.

Had fix, drove slightly more conservatively to be sure the fix wasn't causing any problems

Went back to driving mnormally

Had the remap and on occasion had a bit of fun

 

Looking at the 87th fill up onwards it appears to be improving (though it's rather erratic) so I'd not worry for now

[Robjon]

A bit childish, but........ good fun won't help your mpg figures 

 

Could the increasing fuel consumption be the effect of the increasing amount of fun you are having with your car?

[skoda1982]

Colder weather takes longer to warm up

 

[pinkpanther]

"The Fix" occured between fuel ups 85 and 97, which bizzarely corresponded with a period of reduced variability. I certainly didn't drive any more conservatively following the fix, or any "harder" following the stage 1 remap (excepting a few miles of fun when testing the Torque Pro app / 0-60 / BHP etc).

 

The car's been used for a wide variety of uses over the past 3 years (family trips / holidays / commuting etc) and there have been no major changes in this pattern over this time period.

 

The onset of cold weather (? winter fuel) has seen a drop off in MPG each year, but it's the overall (downward) trend over 3 years / 60k miles which is a concern, especially if it continues.

 

I've just been back and done a similar excercise with the last Yeti (2012 110 BHP TDi 2WD) I ran. I owned this for ~40k miles and see an overall upwards trend in fuel economy over this time - as below:

 

 

[bigjohn]

Stats and stats!

 

If you put your Yeti's first 10 and  last 10 mpg readings into a spreadsheet (hard to read off graph)  and work out their averages they are both very close

 

First 10 42
43
40
44
39
42
38
40
40
45 Average41.3   Last 10 42 36 46 36 44 44 45 41 45 35 Average41.4

Edited 26 November, 2017 by bigjohn

[pinkpanther]

Many thanks for all the comments - I was a little bemused by the difference in trends for the 2 Yeti's.

 

Looking at my current car's fuel returns in a little more detail (broken down into years) I see a downward trend in 2016, but otherwise fuel economy appears fairly static (or even improving) across 2014, 2015 and 2017:

 

Panic over

[Gobmax]

Hi a long time ago My Father's workmate, said don't ever do that again.

I had started  my vehicle up and immediately drove away.

He said the best way to get good Mileage is to let a cold vehicle warm up, before DRIVING OFF.

Having owned 5 Vehicles over the last 50 years, the best advice I was ever given.

If you love your vehicle it will Love you.

 

[lawnmowerman]

43 minutes ago, Gobmax said:

Hi a long time ago My Father's workmate, said don't ever do that again.

I had started  my vehicle up and immediately drove away.

He said the best way to get good Mileage is to let a cold vehicle warm up, before DRIVING OFF.

Having owned 5 Vehicles over the last 50 years, the best advice I was ever given.

If you love your vehicle it will Love you.

 

Not best for the engine though - it can lead to isolated hot & cold spots leading to longer term issues. 

 

Fact.

 

Bill 

[Ootohere]

Gobmax, as i fire up a Euro 6 TDI this morning and switch on the Heated rear Window, Mirrors and then de-ice the glass the coolant will start warming, 

then after happy the glass is clear i will drive off, that might be 5 minutes after starting the engine.

in a few miles the coolant will show 90*oC and after 6 miles the Oil Temp will indicate 50*oC. 

 

?

To warm up the engine for it to achieve a longer life how long do you think it is good to sit ticking over, just that 5 minutes?

[Llanigraham]

10 hours ago, Gobmax said:

Hi a long time ago My Father's workmate, said don't ever do that again.

I had started  my vehicle up and immediately drove away.

He said the best way to get good Mileage is to let a cold vehicle warm up, before DRIVING OFF.

Having owned 5 Vehicles over the last 50 years, the best advice I was ever given.

If you love your vehicle it will Love you.

 

 

Sorry, but that might have been the advice years ago, but it certainly isn't what is recommended nowadays.

[idleness]

Diesels should not be left to idle!

Start and go is the best advice I have been given.

Even having to clear an icy windscreen that's less than 2 minutes for me.

Edited 28 November, 2017 by idleness

[Expatman]

2 hours ago, idleness said:

Diesels should not be left to idle!

Start and go is the best advice I have been given.

Even having to clear an icy windscreen that's less than 2 minutes for me.

Not just diesels. The recommendation is that petrol cars should not be idled for long when started. Of course you need to clear windscreen etc. so in practice I guess most drivers start the car then spend a couple of minutes clearing ice/snow before driving off.

You have to be practical about any recommendations like this, worst thing is to drive off when you can't see clearly, that ways lies accidents and unwanted discussions with the police!

[idleness]

I live in a frost hollow and against perceived wisdom I use hot water to clear my windows. Takes a few seconds and the windows remain clear as they have been "heated". Having said that I will probably get a cracked screen this week a first in 25years. 

[Expatman]

My new SEL- Drive came with heated front and rear screens so waiting to try them. Mind you being retired I tend to wait till frost has lifted before going out!

[kenfowler3966]

My windscreen was used in anger today for the third time.

Fantastic and it doesn’t promptly mist up inside either like previous two Yeti’s

[Ootohere]

Warm Water in 'frosty hollows' not such an issue if the ambient temp rises above freezing that day / night or over the next few days.

Different where it gets in seals of a Skoda and freezes, and each day you add to that, maybe not opening the passenger door and allowing H2o to drain if not frozen.

Then there is pouring water on the ground around your parking place every day, as we know warm water freezes harder.

 

Not just internet myths just UK winters in some areas.

[pinkpanther]

20 hours ago, Gobmax said:

Hi a long time ago My Father's workmate, said don't ever do that again.

I had started  my vehicle up and immediately drove away.

He said the best way to get good Mileage is to let a cold vehicle warm up, before DRIVING OFF.

Having owned 5 Vehicles over the last 50 years, the best advice I was ever given.

If you love your vehicle it will Love you.

 

Many thanks for this. 

 

I do wonder if this advice related to cars running a carburetor? Certainly many of my previous cars had carburetors and some (especially those equipped with Solex carbs) were pretty much "undriveable" until they'd ran for a few minutes and gained a little heat. 

 

Modern cars however constantly adapt to prevailing engine conditions / ambient temperatures and don't I suspect require any warming period, prior to driving off. Certainly leaving my Yeti idling from cold leads to a distinct dieselly smell, related I suspect to over-fuelling whilst cold.

 

Despite this I'm pretty mechanically sympathetic and don't utilise the full rev range of any of my vehicles until the oil temperature is on it's way to a normal operating range (within 3-5 miles in my 1.0 3 pot TSi and somewhat longer in my Euro 5 2.0 TDi). 

[Expatman]

3 hours ago, pinkpanther said:

 

Despite this I'm pretty mechanically sympathetic and don't utilise the full rev range of any of my vehicles until the oil temperature is on it's way to a normal operating range (within 3-5 miles in my 1.0 3 pot TSi and somewhat longer in my Euro 5 2.0 TDi). 

Hopefully no one uses anything but modest revs and light load until the car has reached somewhere near normal operating temperature. Always have understood that using high revs or labouring the engine while cold was a quick way to premature engine problems. Or is that not so with modern fuel injected, computer controlled cars with modern synthetic oils?

[Paul52]

Going back to the original topic, have you tried plotting your graphs as a rolling average of say 5 consecutive readings? This will tend to flatten out variation between fills and might help you identify if and when fuel use started to increase. 

[pinkpanther]

On 28/11/2017 at 22:47, Paul52 said:

Going back to the original topic, have you tried plotting your graphs as a rolling average of say 5 consecutive readings? This will tend to flatten out variation between fills and might help you identify if and when fuel use started to increase. 

Thanks Paul - below is a plot of an average of 5 consecutive readings.

 

Still seems to show an overall downwards trend, starting at approximately the mid-way point?

 

 

[PeterKn]

On 28/11/2017 at 15:24, idleness said:

I live in a frost hollow and against perceived wisdom I use hot water to clear my windows. Takes a few seconds and the windows remain clear as they have been "heated". Having said that I will probably get a cracked screen this week a first in 25years. 

I have long been a fan of the warm water defrosting technique. Almost 50 years ago I used to use near boiling water straight from the kettle on my 1960 Beetle. As there was no demisting available from the air cooled engine until after ten miles or so, I found this also prevented severe condensation at the start of a journey on a frosty winter's night. Everyone told me I would crack the windscreen, but I suppose I've just been lucky all these years, never have. These days I just use tepid water. I am not suggesting anyone else tries this, sure as eggs is eggs it would end in tears. Anyway, my new Yeti se Drive has a heated windscreen, so all I need now is a frosty morning to try it out. 

[lawnmowerman]

2 hours ago, PeterKn said:

I have long been a fan of the warm water defrosting technique. Almost 50 years ago I used to use near boiling water straight from the kettle on my 1960 Beetle. As there was no demisting available from the air cooled engine until after ten miles or so, I found this also prevented severe condensation at the start of a journey on a frosty winter's night. Everyone told me I would crack the windscreen, but I suppose I've just been lucky all these years, never have. These days I just use tepid water. I am not suggesting anyone else tries this, sure as eggs is eggs it would end in tears. Anyway, my new Yeti se Drive has a heated windscreen, so all I need now is a frosty morning to try it out. 

 

Lovely Helensburgh! Helen's Burgh. Right on the River Clyde so keeping you warmer - but frost will come and you will thank your lucky stars for your heated screen.

 

Early October we had sub-zero temperatures and this week we have had snow lying twice (in the Highlands - 12 miles north of Inverness). Heated seats are a godsend too!

 

Bill  

[Lofty79]

Just harking back to the warming up on idle debacle.

Idling from cold is a bad idea when you consider how the top of the engine is fed with oil.

From cold there is little if any oil at the top of the oilways, and the oil will have run off the components for the most part.

The engine is reliant upon oil passing up through small 2mm or so holes in the cam journal..... The cam rests on metal shims/bearings and constantly rubs on them.

Putting the engine under immediate gentle load forces oil to the top faster thus feeding these drier journals and in turn the cam lobes.

The faster this happens the better.

 

I refer to 'bed in' principles when fitting a new cam and followers for example.

These need lubricated asap and the advice is DO NOT LET THE VEHICLE IDLE! The reason being two rough surfaces grinding together needs a supply of oil fast. 20 mins or so of 2500 revs and a few hundred either way keeps it flowing.

 

Idling from cold is this principle in part, the two surfaces are mated so to speak, so less wear occurs, but idling from cold means your relying on these surfaces being mated to not wear too fast. But they are still too dry

 

Bottom line, fast idle and or immediate load (within reason) will bring oil up faster and give it more fling, lengthening the life of the motor, particularly the top end.

 

My 2p worth

[Ootohere]

On these cold days and nights it is good if you have a  safe Outdoor Electric Supply at your parking place and you can plug in your Greenhouse Fan Heater and have the vehicles interior up a few degrees above freezing and then the glass stays frost / ice free on the outside as well.