# Poor Fuel Economy



## bradfordfabia (Jun 14, 2008)

Over the past week the car has been using a lot of diesel,I thought it was because I am putting more strain on the car with using the heaters etc etc but had the car now four winters and never had this trouble before.What could be wrong?. Car is 1.9TDI Fabia and is nearly 7 years old.


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## bizzyfingers (Jul 30, 2009)

Having the same probs in the cold. BMW e46 320d. It happens every winter. I think it is my thermostat.


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## millns84 (Jul 5, 2009)

I've noticed this with our derv too. I put it down to taking forever to warm up in rush hour traffic...


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## Raife (Jul 14, 2009)

Weird, both my Volvo XC90 and my Land Rover Defender love the colder days, run better amd more MPG!


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## Naddy37 (Oct 27, 2005)

I dare not say what mpg I get out mine....


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## Exotica (Feb 27, 2006)

Fact= cars are less efficient in cold temps.


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## stevept (Nov 22, 2009)

Im thinking of getting a performance air filter for my 1.8 petrol c max will they help my mpg or a waste of money for petrol engines


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## davies20 (Feb 22, 2009)

glad its not just my 1.9 that seems to be eating diesel now its cold!!


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## kempe (Jan 9, 2011)

I think its down to the air being cold and more dense, so it puts more fuel in the mix


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## alan_mcc (Oct 28, 2008)

Colder air is a lot denser and contains more oxygen than warmer air.. therefore engines burn much 'fitter' as such so you probably will see a drop in MPG

Hence why performance turbo cars run best on cold/damp days


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## Grizzle (Jul 12, 2006)

Diesels run more efficiently in warmer temps they ove it but if this is the first time in 4 yrs you have noticed then when was its last service? incl fuel filter?

Have you changed your fuel retailer? as i noticed using supermarket diesel i got lower MPG than using Shell.


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## Deano (Jul 7, 2006)

with it being the 1.9 vag engine, it could be your coolant temperature sensor. is your temp gauge reading OK? any hot start probs or lumpy idle?


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## Trip tdi (Sep 3, 2008)

Whats the best diesel retailer going on the market, after all fuel prices is really alot at the moment, so mpg is a important factor, you will find colder climates, any car will take more fuel, specially on startup and whilst its reaching to the right temperature, its takes longer, so more juice is allowed in the engine...

Being cold, its always best to leave earlier, and drive slowly, for mpg but more importantly, safety.


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## andy monty (Dec 29, 2007)

If anything i find my cars MPG improves when i fit the winter tyres.......


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## Grizzle (Jul 12, 2006)

So we just all fit winter tires for more MPG lol.


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## The Cueball (Feb 8, 2007)

love cold weather, my cars run faster... :devil:

still s**t mpg mind you, but I don't really care... :lol:

:thumb:


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## andy monty (Dec 29, 2007)

Grizzle said:


> So we just all fit winter tires for more MPG lol.


it was a pleasing side effect of fitting them i must admit


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## Trip tdi (Sep 3, 2008)

Having the right tyre pressures certainly helps during the year.


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## toomanycitroens (Jan 14, 2011)

Exotica said:


> Fact= cars are less efficient in cold temps.


+1
Absolutely correct, ask any Hauliers it's not only cars:thumb:


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## msb (Dec 20, 2009)

Exotica said:


> Fact= cars are less efficient in cold temps.


Wtf are you for real, lower ambient air temps are the best thing for power end of, heat soak and drawing hot air into an engine is the quickest sure fire way of sapping power and making it run like a bag of ****


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## Trip tdi (Sep 3, 2008)

msb said:


> Wtf are you for real, lower ambient air temps are the best thing for power end of, heat soak and drawing hot air into an engine is the quickest sure fire way of sapping power and making it run like a bag of ****


Are you referring to turbos, super chargers, and intercoolers..


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## The Cueball (Feb 8, 2007)

msb said:


> Wtf are you for real, lower ambient air temps are the best thing for power end of, heat soak and drawing hot air into an engine is the quickest sure fire way of sapping power and making it run like a bag of ****


^^ I think he means in a mpg case...

which he is right....but I'm with you, my car runs better in the cold... but means it uses more petrol... 

:thumb:


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## Trip tdi (Sep 3, 2008)

I would not think having cold weather will make a car quicker than if its warm weather.

I'm sure it depends on the cars engine, plus how it places it's power down....

In the cold, any car takes more fuel, than summer, but in summer we use air con, sometimes the air con on car, does sap power down...

In the cold weather, the car battery takes more toll, the bushes, the oil, plus starting etc... cold weather for a car takes a more battering than hot weather...


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## Ross (Apr 25, 2007)

You should be thankful you don't have a Spec B,struggling to get 23 MGP:lol:


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## Trip tdi (Sep 3, 2008)

This post is not making any sense to me :lol:


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## msb (Dec 20, 2009)

Trip tdi said:


> Are you referring to turbos, super chargers, and intercoolers..


Just cars in general, a well serviced/maintained car will heat up sufficently quickly regardless of outside temperature(isn't that what the thermostat is for?) most cars regardless of fuel type will make more power due to the denser air. The engine will take advantage of the cool air and add more fuel to make extra power so yes in theory you could use more fuel if you are at full throttle all the time(not that thats realistically likely).
But generally it should actually be more economical in cooler temps because the engine isn't having to work as hard as it would on a hot day to produce the same level of performance:thumb:


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## Trip tdi (Sep 3, 2008)

msb said:


> Just cars in general, a well serviced/maintained car will heat up sufficently quickly regardless of outside temperature(isn't that what the thermostat is for?) most cars regardless of fuel type will make more power due to the denser air. The engine will take advantage of the cool air and add more fuel to make extra power so yes in theory you could use more fuel if you are at full throttle all the time(not that thats realistically likely).
> But generally it should actually be more economical in cooler temps because the engine isn't having to work as hard as it would on a hot day to produce the same level of performance:thumb:


MSB, i just read this, and it does make sense, i agree with yourself :thumb:


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## msb (Dec 20, 2009)

Put it this way if you had ever seen how heat soak kills an engine on the rollers you would understand completely where i'm coming from


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## The Cueball (Feb 8, 2007)

Ross said:


> You should be thankful you don't have a Spec B,struggling to get 23 MGP:lol:


and you should stop moaning and try and live with 12mpg



:lol:


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## msb (Dec 20, 2009)

thanks trip:thumb:


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## Derbyshire-stig (Dec 22, 2010)

Maffs are popular on vag(i know seat) tdi`s


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## Ross (Apr 25, 2007)

The Cueball said:


> and you should stop moaning and try and live with 12mpg
> 
> 
> 
> :lol:


:lol: I have seen it do 18 MGP:driver:


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## Trip tdi (Sep 3, 2008)

Maffs, they are common on vags.


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## Laurie.J.M (Jun 23, 2011)

stevept said:


> Im thinking of getting a performance air filter for my 1.8 petrol c max will they help my mpg or a waste of money for petrol engines


Depends which type you go for, if you go for the boy racers favourite cone filter you will actually loose power and the engine will become very unresponsive and lethargic at low revs. If you fit a good quality performance panel filter there should be a small increase in power and response and possibly better fuel economy. On a small capacity N/A engine the difference won't be that big or noticeable, it's on turbocharged and supercharged engines where the difference is more noticeable.


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## msb (Dec 20, 2009)

what are you lot playing at used to be able to get my old tuned m3 down to 7 mpg when driving it really hard Lol


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## The Cueball (Feb 8, 2007)

msb said:


> what are you lot playing at used to be able to get my old tuned m3 down to 7 mpg when driving it really hard Lol


I'm talking taking it easy!!! :lol:

3 - 5 in the XKR when on a charge :doublesho:doublesho

haven't tried in the S8 yet... still waiting to service it...

:driver::driver::driver:

:thumb:


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## Ross (Apr 25, 2007)

I have a K&N panel filter on the Spec B and it has made a noticeable difference:thumb:


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## stevept (Nov 22, 2009)

its k&n panel filter im looking at


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## msb (Dec 20, 2009)

enclosed induction kits or panel filters are the only way to go imo, open induction kits draw to much warm air in


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## stevept (Nov 22, 2009)

ross what kind you got, sorry if i sound daft but whats a spec b


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## Ross (Apr 25, 2007)

Subaru Legacy with a 3 liter flat 6 at the front:thumb:


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## Lee.GTi180 (Apr 28, 2010)

My 1.9 tdi Fab is fine so far, on my 450 mile weekly commute I'm still getting 55mpg.


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## stevept (Nov 22, 2009)

how much diffference have you seen ross.
mines only a 1.8 so might not see a massive difference


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## Techgeek (Jun 7, 2007)

Try changing the thermostat and making sure its got the right oil. I gained roughly 2 mpg average changing to fully synthetic 10w30 from the 20w50 asda crap the previous owner put in. Also i'm sure i read somewhere the oil companies add additives to diesel to prevent gelling dependant on how cold a winter is forecast and the additives reduce mpg.


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## Soapie (Aug 26, 2009)

Focus ST's first winter down to 28.6 Avg MPG from 30.4


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## hibberd (Jul 5, 2006)

Check, or have checked the EGR thermostat is not mis-functioning, and check the main thermostat at the same time.


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## piotrtdi (May 3, 2011)

My car Audi A3 2.0 TDi 170 avg


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## Trip tdi (Sep 3, 2008)

Thermostats don't really go on vags, the coolant sensor is a common problem with them, your temperature gauge, is it in the middle when warmed up, does it go down and up at all whilst driving.

what mpg are you receiving plus what model engine is yours, diesel wise, bhp.

I can't see having winter tyres, will increase mpg, it will increase traction in the cold weather and better grip.

Has your car been serviced at all.


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## Claireeyy (Jul 20, 2009)

Sounds like it needs a good service to me.


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## Trip tdi (Sep 3, 2008)

Having a good service, you will benefit from a little mpg gain, not a massive difference, but the car is fully maintained then, such as the oil and fluids in the car.

Really this needs diagnosing, how does the car drive, power wise, any jerkiness whist acceleration, hows the start up on the car, any smoke blowing from the rear exhaust, there needs to be more info on how the engine is behaving, what fuel have you used, but that will not make a major difference but i thought i would try my best on this one.


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## dubber (Oct 2, 2011)

As trip said u need to have it plugged into vagcom, could be a number of things. Knock sensor, lamba, airflow etc


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## bradfordfabia (Jun 14, 2008)

Claireeyy said:


> Sounds like it needs a good service to me.


The car had a service in November , how much does a new thermostat costs?.

The past few weeks the car has been sluggish to start but put this down to maybe needing a new battery.


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## Deano (Jul 7, 2006)

bradfordfabia said:


> The car had a service in November , how much does a new thermostat costs?.
> 
> The past few weeks the car has been sluggish to start but put this down to maybe needing a new battery.


i'd be looking at the coolant temp sensor mate, same happened on my A4.:thumb: genuine part is about £30


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## Claireeyy (Jul 20, 2009)

bradfordfabia said:


> The car had a service in November , how much does a new thermostat costs?.
> 
> The past few weeks the car has been sluggish to start but put this down to maybe needing a new battery.


£20 I think.

Were the glow plugs changed too? Is the battery light coming on?


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## bradfordfabia (Jun 14, 2008)

Is fitting a thermostat easy or do I need to take it to a garage?.

No battery light coming on, glow plugs not been replaced.


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## Trip tdi (Sep 3, 2008)

Its more likely not your thermostat my friend, it could be, but on vags they don't normally go.

Are you referring to the coolant temperature sensor, if so thats in green in colour.

Glowplugs, does it start fine on cold.


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## bradfordfabia (Jun 14, 2008)

It starts every time even the coldest mornings.


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## Trip tdi (Sep 3, 2008)

Its not the glowplugs then, battery is fine, starter motor no problem.

How many miles are you getting out of a tankful, comparing to summer and this season now ?


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## bradfordfabia (Jun 14, 2008)

Well a week ago on the Monday I filled up the car and by Saturday it was about 60 miles left in the tank after driving 250 miles. In the summer if I fill it right up it takes 100 miles even for the needle to move, so at least 450 miles on a full tank summer.


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## Trip tdi (Sep 3, 2008)

bradfordfabia said:


> Well a week ago on the Monday I filled up the car and by Saturday it was about 60 miles left in the tank after driving 250 miles. In the summer if I fill it right up it takes 100 miles even for the needle to move, so at least 450 miles on a full tank summer.


Well judging by your miles, something does not seem right to me, whats the mileage on the car, plus bhp, are you loosing any power on the car whilst placing some throttle.
Is the car in question, driving different in any way, power wise, noise from the engine.

When was the last time you had a service done to the car.


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## msb (Dec 20, 2009)

bradfordfabia said:


> Well a week ago on the Monday I filled up the car and by Saturday it was about 60 miles left in the tank after driving 250 miles. In the summer if I fill it right up it takes 100 miles even for the needle to move, so at least 450 miles on a full tank summer.


if you're using that much extra fuel it would indicate to me theres some sort of problem, weather temperatures shouldn't affect mpg that much:thumb:


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## Trip tdi (Sep 3, 2008)

msb said:


> if you're using that much extra fuel it would indicate to me theres some sort of problem, weather temperatures shouldn't affect mpg that much:thumb:


I totally agree the weather temperatures now should not have a major effect on the mpg by that margin; i was giving my best attention on this thread, something to me does not add up, i would say there is something wrong with your car, its not running to the right spec plus perimeters, take the car to a garage and it needs diagnostics to get to the bottom of this, sometimes diagnostics are a rough indicator, some will not throw a code out just beware.

You could try, a injector cleaner in the car, someone else has mentioned this in this thread, but i don't think you will see a major benefit from this, additives are a hit and miss, not to sure if this will cure you problem, but for a region of 6 pounds could be worth it, a try and error if you are on a budget, but don't mark my words if that will work.

Could be a number of factors affecting the car, or simply one electrical component such a coolant temperature sensor, but by that mileage i don't think that will be the cause.


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## PugIain (Jun 28, 2006)

It wont be glow plugs.Theyre more likely to cause poor starting in a diesel.
As the glow plugs are only actually in use at start up and not to keep the engine running.
Id get it checked out rather than just having a guess.


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## Trip tdi (Sep 3, 2008)

Has the Fabia been serviced at all, when was the last one, and when is the new one due, whats the mileage on yours....


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## bradfordfabia (Jun 14, 2008)

Service was in November had oil change and new air filters. Last night before I locked the car up I revved it up to see if I could hear anything not right, all seemed ok. This morning I started early so the roads was quiet so I turned off everything apart from the lights and cruised down the road for a mile and half in 5th gear like I do in the summer before I have to really press the brakes, in summer the trip computer says 110+mpg and today it read 100mpg so not to bad.


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## bradfordfabia (Jun 14, 2008)

Trip tdi said:


> Has the Fabia been serviced at all, when was the last one, and when is the new one due, whats the mileage on yours....


Mileage is about 52000, car is 7 yrs old next month.


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## Gruffs (Dec 10, 2007)

Unplug the Maf sensor and go for a drive. If it is better, you know the Maf is giving false readings.

I'm sure Briskoda or seatcupra.net would have seen this fault before too.


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## bradfordfabia (Jun 14, 2008)

Been for a spirited run round country lanes , I have put my foot down on straight roads , the turbo kicks in ok and it's not sluggish. The needle on the gage did not move, maybe it's ok now


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## Trip tdi (Sep 3, 2008)

bradfordfabia said:


> Been for a spirited run round country lanes , I have put my foot down on straight roads , the turbo kicks in ok and it's not sluggish. The needle on the gage did not move, maybe it's ok now


Thats very bizarre there, i seriously thought there was issues with the car, glad the car is running how it should do.
As the needle gauge is not moving, there's no problem then, just place some injector cleaner in the car, it might help...
I can't really see a country lane blast, rectifying this, with the foot down job you mentioned, due to the mileage from summer and winter, sorry to say this as i have.

I honestly thought there was a problem with your car, but it seems fine now, personally i don't understand how the car is running normal now...


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## Gruffs (Dec 10, 2007)

Could this be explained be a dodgy earth somewhere? Have you been using your rear wash/wipe a lot? Is it a bit rubbish.

There is a connection at the back of some VAG car that is known to fail and leak screenwash inside the car.

Perhaps it has dried out and the car is now working OK?


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## bradfordfabia (Jun 14, 2008)

Trip tdi said:


> Thats very bizarre there, i seriously thought there was issues with the car, glad the car is running how it should do.
> As the needle gauge is not moving, there's no problem then, just place some injector cleaner in the car, it might help...
> I can't really see a country lane blast, rectifying this, with the foot down job you mentioned, due to the mileage from summer and winter, sorry to say this as i have.
> 
> I honestly thought there was a problem with your car, but it seems fine now, personally i don't understand how the car is running normal now...


I will see how it goes over the weekend, lets hope it is ok now. Only been using the rear wiper when I have really needed it.


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## bradfordfabia (Jun 14, 2008)

Gruffs said:


> Could this be explained be a dodgy earth somewhere? Have you been using your rear wash/wipe a lot? Is it a bit rubbish.
> 
> There is a connection at the back of some VAG car that is known to fail and leak screenwash inside the car.
> 
> Perhaps it has dried out and the car is now working OK?


He was asking about the wiper.


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## DIESEL DAVE (Jul 26, 2007)

bradfordfabia said:


> Over the past week the car has been using a lot of diesel,I thought it was because I am putting more strain on the car with using the heaters etc


Most if not all diesels use more in the cold weather, apart from normal poor cold efficiency I put a lot down to the winter additives put in to stop the fuel freezing/waxing in very cold spells.


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## Ross (Apr 25, 2007)

Give it a good thrashing when its warmed up:thumb:


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## Trip tdi (Sep 3, 2008)

Ross said:


> Give it a good thrashing when its warmed up:thumb:


A good thrashing on a vag engine, juts make sure the intercooler pipe does not come off :lol:

Seriously it might help your car by placing some v power diesel, the cars serviced in November, just give some throttle response, you've done that, and you have admitted its sorted the problem out.


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## Ross (Apr 25, 2007)

I thought VAG cars where supposed to be reliable?:lol:


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## Trip tdi (Sep 3, 2008)

They are reliable ross, to a extent, a good thrashing in my books normally means the intercooler pipe pops off :lol:


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## bradfordfabia (Jun 14, 2008)

Ross said:


> Give it a good thrashing when its warmed up:thumb:


Yeah don't worry I did:thumb:


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## Ross (Apr 25, 2007)

bradfordfabia said:


> Yeah don't worry I did:thumb:


So do I ,the flat 6 is just too tempting :lol:


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## Ross (Apr 25, 2007)

Have you thought about trying this? http://www.millersoils.net/M3_cgi/m...d=203&exact_match=on&type=automotive&cart_id=


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## Trip tdi (Sep 3, 2008)

bradfordfabia said:


> Yeah don't worry I did:thumb:


Is your car all sorted now...:thumb:


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## carrera2s (Jun 28, 2009)

Ross said:


> Have you thought about trying this? http://www.millersoils.net/M3_cgi/m...d=203&exact_match=on&type=automotive&cart_id=


I have just started using on my vitosportx van 3.0ltr V6 Diesel

Runs smoother, sounds quieter and slight increase in mpg!:thumb:


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## Trip tdi (Sep 3, 2008)

I just really don't know how the mpg came back, did it come back by a little footdown job.


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## bradfordfabia (Jun 14, 2008)

The last week or so the car is back to normal economy, thankfully. I wonder what caused the car to use sp much diesel?.


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## Ross (Apr 25, 2007)

Did you have a cold snap weather wise?


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