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TomsFocus

Sudden Drop in MPG

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Ok, so I know it's been chilly this week, but over the last tankful (3 weeks) I only got 52mpg.  That's a 10% drop compared to the previous tankful.  To put it in perspective I've lost 50 miles on this tank and paid an extra penny for every mile.  Thought the MPG reader needed a reset but it was the same calculated properly.

Filled up yesterday and have done my usual roads on Tue and Wed (about 40 miles) and the reader has only just scraped 52mpg when I got back this evening, would expect 56/57mpg by now.

Is anyone else experiencing this massive sudden drop in MPG or should I be looking for something broken? :unsure:

Only thing I can say so far is both the latest tanks were Sainsburys instead of my usual BP, but I'm sure I haven't noticed that amount of mpg loss with Sainsbury's before.

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42 minutes ago, TomsFocus said:

Ok, so I know it's been chilly this week, but over the last tankful (3 weeks) I only got 52mpg.  That's a 10% drop compared to the previous tankful.  To put it in perspective I've lost 50 miles on this tank and paid an extra penny for every mile.  Thought the MPG reader needed a reset but it was the same calculated properly.

Filled up yesterday and have done my usual roads on Tue and Wed (about 40 miles) and the reader has only just scraped 52mpg when I got back this evening, would expect 56/57mpg by now.

Is anyone else experiencing this massive sudden drop in MPG or should I be looking for something broken? :unsure:

Only thing I can say so far is both the latest tanks were Sainsburys instead of my usual BP, but I'm sure I haven't noticed that amount of mpg loss with Sainsbury's before.

Its quite possible a slow leak in one of your tyres. I've got one, and it ruins the MPG horrifically, check yer tyres.

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My Fiesta 1.5tdci . I travel 33 miles each way to work. When I got to work Monday I reset the mpg . Now 166 miles later it shows 65.2mpg.  In the past it would normally be about 63mpg most of the time. (it is always showing about 5% higher than a real calculation based on what I put in the tank). So my mpg has improved but I think it might be darker rainier weather means people are driving slower and holding me up on the dual carriageway / motorway so my car is travelling at a more economical speed. 

As the lights are now on and the heater fan etc there is theoretically more drag on the engine from the alternator. I have heard people say that in winter there are different additives in diesel fuel to stop it waxing at low winter temperatures which lowers the mpg but I do not know if there is truth in that

 

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39 minutes ago, CrazyInWeston said:

Its quite possible a slow leak in one of your tyres. I've got one, and it ruins the MPG horrifically, check yer tyres.

Good point!  I had 4 new tyres last month though, none leaking yet.  They're also the same size, make and model as the old ones so there shouldn't be any difference from the tyre change.  

6 minutes ago, isetta said:

My Fiesta 1.5tdci . I travel 33 miles each way to work. When I got to work Monday I reset the mpg . Now 166 miles later it shows 65.2mpg.  In the past it would normally be about 63mpg most of the time. (it is always showing about 5% higher than a real calculation based on what I put in the tank). So my mpg has improved but I think it might be darker rainier weather means people are driving slower and holding me up on the dual carriageway / motorway so my car is travelling at a more economical speed. 

As the lights are now on and the heater fan etc there is theoretically more drag on the engine from the alternator. I have heard people say that in winter there are different additives in diesel fuel to stop it waxing at low winter temperatures which lowers the mpg but I do not know if there is truth in that

 

Think I'd move nearer work lol!  Though a long, steady journey is obviously good for your fuel consumption.  

I did think about more load with being winter but I've only used the heated screen once so far this week, not used heated seats or AC and only had the heater temp on halfway (not entirely sure if there's an electric heater for before the coolant is warm enough).

Winter fuel additives are a good shout, I think they do still use them, probably more so now they put a good amount of bio in which isn't good in low temps.  Other people should be experiencing the reduced MPG if it is the fuel though...

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It is fair to say that diesel engines take longer to reach optimal engine temps during the winter months. Watch how long it takes the temp gauge to reach use position compared with summer use.

I know my MPG suffers during the autumn winter period.

From the AA http://www.theaa.com/motoring_advice/news/aa-fuel-for-thought-increased-cost-of-winter-motoring.html

Fuel facts

To help drivers understand better the impact of winter driving on their fuel bills, the AA Fuel for Thought campaign offers the following facts:

  • The heated rear window uses around two per cent extra fuel. If both the front and rear heated screens are used the increase in fuel consumption equates to six per cent as heated front screens consume more power than the rear screen.
  • Even at a relatively mild outside temperature of +10C, a car's fuel consumption for the first mile will be around 40 per cent higher than with a warmed-up engine. This falls to around 16 per cent over the next three miles and, even up to 6.5 miles from start-up, fuel consumption can be 8 per cent higher.
  • The increase in fuel consumption due to cold weather is similar for both diesel and petrol cars. AA tests show extra fuel use after 1 mile and 3 miles respectively are:
    • typical small petrol car – 34% and 17%
    • medium petrol car – 38% and 16%
    • small diesel car – 32% and 12%
    • medium diesel car – 43% and 18%
  • For demisting windows and getting the cabin comfortable, basic air conditioning on a small car can increase fuel consumption by up to 10 per cent. A more powerful petrol engine will suffer less, as will a larger diesel.
  • Getting stuck in a traffic jam is another daily problem with winter driving. Even with a warmed-up engine, a petrol car can lose at least two-thirds to three-quarters of a litre of fuel every hour, or 1.2 to 1.4p a minute. A diesel car can lose a third to half a litre of fuel an hour, or 0.6 to 1.0p a minute.

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I know it'll be worse in winter, but not usually this bad, it's not even that cold yet really.  Just checked last year's MPG spreadsheet and I was still doing 55mpg in Nov and Dec.  May as well have bought an ST at this rate... :rolleyes:

IMG_20171110_111839.thumb.jpg.818f4e61aad4486d989087ed2e0a6fba.jpg

 

5a0592a5e8c44_FocusMPG.jpg.34fa3fd55900013a08c27658df3ae792.jpg

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Here's my spreadsheet for this year so far, definitely a drop over the winter months as you can pick up in the graph below, but not too bad overall.  the average in the 9 years since I have had the car is 61mpg but the economy figures really improved a couple of years ago with a EGR/DPF sorted out and a remap, as well as it now pulling a lot better.  I think that regular oil/filter and air filter changes, and keeping the tyre pressures on the high side (40psi) really help as well.

image.png.373aca29e3c790ac8c77cafc991ab0e8.png

 

image.png.85e059f6aebaf864a8b52ff215939100.png

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Glad I'm not the only one with an MPG spreadsheet! :laugh: 

I am jealous of your MPG though lol, in 3 years mines never hit 60mpg over a tank let alone averaged it. :sad:  I'm at 55.5mpg average over 38 months and 27k miles so far.  

I do 6k oil changes, and it had a major service about 4k ago so the recent drop shouldn't be due to needing a service.  Tyres are kept at 32PSI, I find any more than that makes it loose and floaty at speed.  What size tyres do you have for 40PSI?  Is it just you or carrying extra weight as well?

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Yeah, I got into the habit years ago, using a notebook and pencil at every fill but since moved hi tech with the spreadsheet!  It is useful to see how it varies - when it has dropped suddenly this has either because I did a long trip with a trailer or was in a rush and drove a lot faster than I should have, but it also happened once when my DPF clogged, which pushed me to sort it out it as it wouldn't have been evident straight away what with no DPF light on the Mk 2 Focus.

I normally drive with just myself in the car, but do sometimes have heavy loads in the boot or pulling a trailer but keep the tyres at about 40psi at all times anyway.  I haven't noticed any issues with ride quality (maybe just feeling the bumps a bit more) and no premature or uneven wear,  except once when one wheel was not correctly balanced.  I use Michelin Primacy or Energy+ and they last a good 40k miles per set.  I do 13 miles each way to work, and regular longer trips and don't really drive in slow town traffic, mainly good flowing A road which I think really helps the economy as well.  I have a choice of two ways to get to work and take the one with less roundabouts as that is where all the jams are, and the start/stop also kills the economy.

 

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Each to thier own regarding the tyre pressures I guess!

I tend to do the same sort of driving, taking slightly longer routes to avoid traffic and roundabouts.  Mostly in steady flowing traffic but once a week I do drive to Tesco 2 miles away...bad I know but I'm not walking 2 miles with 25kgs of shopping lol.  

I use Dunlop SportBluresponse tyres which are B rated for economy (A for wet grip which was the priority) but I do wonder if your Michelin's are worth a couple more mpg.

Have you taken any notice of your average speed if the PFL shows it?  Mine sits at about 26mph which always seems low but nothing to compare with.

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From memory the average speed sits in the 30s but will check when I go out later.  It always feels low, but then it doesn't take a lot of start/stops to really drop down the average from the steady 60/70mph on the open road.  the first and last half mile is probably only doing at 20mph in residential or industrial zone setting.

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I keep a spreadsheet and have used it for last 14 months , 17,500 miles.  Fiesta 1.5tdci, average mpg between 60 - 60.5mpg. 

These modern cars are nice and economical but maybe not always as much extra mpg compared to older cars as some people might think.

In about 2001 I had a 1984 Fiesta Mk2 1.1L with Four speed gearbox (The old OHV engine with VV carb).  I used that for a year doing the same work journey I do now on same roads (33mpg each way) and kept a note of every litre/gallon of fuel that I put in it and it did 47mpg average over the whole year I used it. And being 4 speed the engine was screaming away on the motorway. (it used a gallon of oil per month, it never really looked all that smokey, just a little now and then, but if it uses oil like that there is no need for an oil change as you're changing the oil by keeping adding new oil so often)

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Shell V power diesel actually worsens my mpg. is that meant to happen. lol i add millers diesel plus to it too.

56 mpg is the best i have achieved. 

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On 11/10/2017 at 2:04 PM, TomsFocus said:

Have you taken any notice of your average speed if the PFL shows it?  Mine sits at about 26mph which always seems low but nothing to compare with.

 

Mine is at 33mph average speed, which I don't think I have ever reset.  Maybe that is where the difference is because of different driving conditions?

 

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1 hour ago, south_bound said:

 

Mine is at 33mph average speed, which I don't think I have ever reset.  Maybe that is where the difference is because of different driving conditions?

 

Yeah I reckon you're right, I must do more slow driving than I thought!

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So, down to 48mpg currently... :sad:

It was cold this morning though...2c...using 0.3 gallons/hour at idle after startup, its usually 0.1g/h!  It also never warmed up on my gentle 6 mile run, bit of town followed by single track lanes, speed between 20-40mph most of the time.

As soon as I get the chance to put my foot down the temp rises to the centre and stays there though, so I don't think the 'stat is stuck open.  It just seems to be too thermally efficient under light load. :unsure: 

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I've wondered before if it is best to take it gentle in the first few miles to let the engine warm up gradually, or let the revs stay higher to get the engine hot quicker (I'm not talking about red-lining it or anything, just working it a bit harder).  I don't think the dash reading is accurate enough over a short trip so I would have to do it every day for a week or two to see what the difference is.  I might try it if I remember.

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I stopped buying Supermarket grade fuel years ago after a pal showed me the inside of a petrol and diesel fuel filter after a year of use.

Some people may think i'm wrong but it's only what i've been told, read and seen with my own eyes.

Supermarket fuel is a lesser grade. Legal yes but not filtered as much as BP, ESSO and Shell.

I did have issues with my old TDCI which had a gunked up filter in the fuel tank as well as a worn diesel pump too.

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On 21/11/2017 at 10:54 PM, JamesMalin said:

I stopped buying Supermarket grade fuel years ago after a pal showed me the inside of a petrol and diesel fuel filter after a year of use.

Some people may think i'm wrong but it's only what i've been told, read and seen with my own eyes.

Supermarket fuel is a lesser grade. Legal yes but not filtered as much as BP, ESSO and Shell.

I did have issues with my old TDCI which had a gunked up filter in the fuel tank as well as a worn diesel pump too.

Due to funds i have been using asda diesel eeeep but as usual with millers diesel additive

 

If my wallet allows its bp ultimate or shell v power

 

Jamie

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Heres some more completely anecdotal evidence of MPG improvment, since I had my alternator changed, my MPG has risen by about 10%. she also feels like she is less sluggish.

I have a big drive tomorrow so itill be interesting if I can get her back above 60MPG

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I haven't used the car much this week so it's just up to 275 miles from this tank now, currently at 51mpg.  Still another week and a half to go I reckon, and when I calculate it, I won't be surprised if it's 52mpg again like the last one.  Will probably try BP again then just in case it is the fuel.  I still don't think it's cold enough to be causing such a reduction yet.

There was an odd noise from the belt end this evening though, inching along in traffic on a cold engine it started making what sounded like a high pressure air leak but only as I put it under load moving on the clutch...was more of a squeak than a chuff but could be an injector leak.  Don't think it's a boost leak.  Whatever it was stopped after about 10 minutes so I'll just hope it was nothing for now. :rolleyes:

 

 

 

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Tom don't know what your doing wrong with your tdci currently getting over 67 mpg on the trip and around 60 real life mpg with mine ha! Currently freezing out aswell! Mpg has dropped a bit since the summer and expect to fall a little bit further during the cold months.  

IMG_20171123_213942.jpg

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18 hours ago, james_60 said:

Due to funds i have been using asda diesel eeeep but as usual with millers diesel additive

 

If my wallet allows its bp ultimate or shell v power

 

Jamie

As long as you don't use Morrisons diesel regularly you should be fine mate.

Morrisons use the full 7% legal allowance of bio-diesel in their fuel which means more soot, more carbon build up, less bang for yer buck and more chance of yer fuel filter clogging in really cold weather. :wallbash: (It annoys me that they don't price any cheaper than the other supermarkets despite their diesel being inferior to all the others).

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