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Loss Of Mpg.

39 posts in this topic

i'm hoping someone can help because this is doing my nut.my car is a focus 2005 1.8 diesel.i've just given it a 70,000 service(oil/air filters and europarts engine oil 5w30).was getting anything from 51 to 54 mpg.and now i'm lucky to get 40 mpg.i can acually see the fuel gauge going down slowly when driving.

so if anyone has an idea,that would be great as have a 500 mile trip to do next month.cheers guys.

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try re-setting the ECU? unplug the battery for 30 mins then plug it back in. keep your radio code to hand! thats not good mpg though! im getting more than that from my 1.8 petrol!!!

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yeah have tried that 4 times,but still the same.

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Its a "learning" ECU, so it takes a bit of time for it to "learn" (different conditions etc)

the colder weather can have an effect on MPG because a diesel has a better MPG once its warmed up, it can take a long time to warm up in cold weather (if it ever really does) especially for short trips

Winter diesel has anti-freeze in it and there is a small? drop in mpg with this too

Same with winter tyres (more drag)

Check your brakes are not binding and your tyres are at the highest recommended pressure

try resetting your avarage MPG, round town driving can drop the avarage down

are you driving harder, more weight in the car, or shorter runs, round town or in heavy traffic -

seems a big drop in MPG though

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With the cold weather diesels take far longer to warm up and it effects mpg just as it does in a petrol it may be the cold and nothing more also check the underneath of the fuel tank for any leaks

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thanks for your reply guys,foca,i have been getting 50+ mpg even in really cold weather.tyres are at 35psi, and brakes are not binding.have done a 70 mile trip this morn and the mpg has gone down to 37.9.i'm driving the same roads in the same way,of the 2 i'm driving MORE carefully.and artscot79,i used to leave it running for 15 mins in cold weather to warm up a bit before going for a trip and still got 50+ mpg.no leaks under the car either.is there a fuel sensor somewhere on it that maybe on it's way out.thanks for your replys guys..

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very strange indeed then have you checked the air filter is housed correctly and alls tight

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yep just had a look,and it's all fine.

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Has this MPG been validated by manual calculation (brimming the tank and crunching the numbers) or is it just what the trip computer says ?

I use an app to work out my fuel economy, and I check that figure back to what the trip computer says.

In the summer my trip computer was accurate to 1%

Now it's colder, my trip computer is out by 10% (it says 45, actual is 50).

Maybe this has something to do with it?

And diesel fuel economy does suffer in cold weather, as the engine takes so long to warm up

You say you can actually see the fuel gauge going down. Perhaps is was also doing this before, but you didn't notice it?

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i must admit pitmonster i'm going what the trip says,havent done the full tank way yet, no the gauge has always been steady when driving,it makes me wonder weather the gauge is faulty.it's only gone wonky since it's had a service.i've put europarts own engine oil in the car,now i'm no fitter but have been told to change the oil to a better make??. thanks for the advice pitmonster.

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try re-setting the ECU? unplug the battery for 30 mins then plug it back in. keep your radio code to hand! thats not good mpg though! im getting more than that from my 1.8 petrol!!!

are you sure your not driving a diesel?? lol you get more than 40mpg in a 1.8 petrol?? i struggle to get 26mpg haha

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Such a large drop would posssibly indicate a blocked air filter, so since it is a new filter is there any chance of a partial blockage somewhere before or after?

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good shout StanH,will have a look later.

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well have had a good look at the car today,and i'm still nowhere nearer than when i started.so tomorrow going for a drive as pitmonster suggested then after that i dont know..................................

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In cold weather the car will pump in more fuel to compensate for the denser colder air.

In the summer I can get 500 miles to a tank but in winter it drops by about 40-50 miles.

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i can see your point,but this loss of mpg has only started since it had a service.

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In cold weather the car will pump in more fuel to compensate for the denser colder air.

In the summer I can get 500 miles to a tank but in winter it drops by about 40-50 miles.

I'm seeing the same results, and it was the same last winter

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In cold weather the car will pump in more fuel to compensate for the denser colder air.

In the summer I can get 500 miles to a tank but in winter it drops by about 40-50 miles.

You are only assuming the denser colder air is the reason for the drop in MPG, it may be insignificant and the reason for the loss of mpg in the winter is the winter diesel we are supplied (with antifreeze added), or the fact modern diesels take so long to warm up in the winter (and don't return a good MPG untill they are warmed up) the last point is the most likely cause (or it may be because of several reasons working together)

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so assuming foca that your right (im not saying your wrong)would that account for me losing about 15 mpg.

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so assuming foca that your right (im not saying your wrong)would that account for me losing about 15 mpg.

I don't think so, in my experience these things only make a few MPG difference (say 5mpg?/ 10%) and would not make as much as 15MPG difference, if it is correct mabee there is something wrong and the garage has caused your loss of MPG in some way?

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Hi Folks

Just my pennys worth

Did they adjust the handbrake.

If the shoes are unevenly worn and it isnt balanced it could be partially on, on one side.

Check how hot your drums are after a 10 mile run. be carefull because they could be red hot

Jamie

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No james all the wheels and brakes are fine.sorry to keep ranting on,but just bin on a 30 mile trip,and i'm sitting in the car.37.7mpg was on the dash and within 45 seconds it had gone down to 34.2mpg.now,i'm starting to think this has to be electrics.any ideas.

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Have you done an actual calculation yet, or is this all based on trip computer numbers?

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If this is based on the trip computer which i think it is then its not a correct value

Only A Brim to Brim result will give an accurate figure.

That is why i use Spritmonitor.de (see my mpg figure)

Its low because i have a lead foot (not saying you have a lead foot)

Jamie

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no pitmonster it's done on the trip,my dad went into hospital sunday night and havent had the time to go for a tidy drive.hoping to do it some time this week.

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