Car mechanic brain needed

16
Found 7th Jan
I got a Citroen C3 diesel 1.6, the on-board computer can give you how much mileage you got left depending on your fuel tank. Until recently, when i fill up to the max, the computer used to display once i was cruising on the motorway up to 980 miles (i know that it never achieves this) but lately after filling up, it does not reach that figure anymore, more like 790 miles. Usually out of a full tank i managed to do 600 miles, with maybe 50 to 60 miles left in the tank and it's when i go to the petrol station to fill it up again. On the last tank i had to go when i just finished 500 miles, my driving habit is still the same, not faster. Also usually the first notch on the tank goes down after around ~145 miles, yesterday it went down at about 110 miles.
Do you think the diesel injectors needs cleaning somehow or could it be something else
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Has this happened in the last 4-6 weeks? Was it fine before that?
GAVINLEWISHUKD1 m ago

Has this happened in the last 4-6 weeks? Was it fine before that?



yep last 4 weeks
Its been cold..very. Diesel engines take longer to warm up and will use more fuel. The quality of the diesel can also affect consumption. I drive diesel cars and seem to be using more fuel of late..
probably that holiday weight you put on aye


no but tyres can lose pressure in cold weather, and tyre pressure can affect efficiency
any extra weight will reduce efficiency
cold weather reduces efficiency (engine has to stay warm)
if you have the heater in in the car, that's not magic and will use fuel (same with AC)
cold air is more dense than warm so you have more drag
when our brains switch to "safe mode" i.e let's go 30 in this 50 area because it may be icy - efficiency is reduced
Splodger1013 m ago

Its been cold..very. of late..


ok just seems quite a bit of a difference. I guess i could use one of those cleaner that you put in your tank when you fill up, not sure how effective they are, but it would not hurt
jeannot1810 m ago

yep last 4 weeks


It's cold weather. It will return to normal when the weather gets warmer.

If you want to help it out you can cover a third of the radiator with either plastic or card covered in gaffa tape and cable tied to it. This will help the engine warm up quicker and keep the engine warmer while driving. Once the weather jumps above 7°c it's time to remove it.
murtgurge3 m ago

probably that holiday weight you put on aye no but tyres can lose …probably that holiday weight you put on aye no but tyres can lose pressure in cold weather, and tyre pressure can affect efficiencyany extra weight will reduce efficiencycold weather reduces efficiency (engine has to stay warm)if you have the heater in in the car, that's not magic and will use fuel (same with AC)cold air is more dense than warm so you have more dragwhen our brains switch to "safe mode" i.e let's go 30 in this 50 area because it may be icy - efficiency is reduced



Actually i lost 8 pounds over Xmas! Yes i should check the tyre that's a good point, i did not know about the normal heating making the consumption higher (i knew about the AC)
Well spotted - but keep watching as "one swallow does not make a summer".

As others have said colder weather will impact consumption but you also may have had a 'poorer' tank of diesel. If there is no improvement over the next month or so (assuming 2/3 tank fills over that time) then I'd have a go at adding some cleaner fluid for the injectors (variable reports whether this stuff actually works but it's a cheap attempt at a solution).

Edit: ps - well done on the weight loss!
Edited by: "Van1973" 7th Jan
Thanks guys, that's been helpful. Love my little car, it has been probably the most economic car i have ever had and just want to keep that way
Other thing to bear in mind is driving in wet and windy weather will consume more fuel as there is more resistance on the car! If your worried about engine performance try a shot of cataclean (for engines with DPF’s). It will improve things slightly but also remember that fuel in winter is a slightly different mix than the fuel you get in the summer.
When was it last serviced , was the air filter changed
Alsomight be worth buying a diesel injector cleaner , we usually use a Wynn's one
Are all the tyres pumped up to correct pressure ?
I get the car serviced always on time, I have checked the tyre this afternoon and there was nothing much missing really. I guess it is the cold weather effect. Will compare when the weather starts getting a bit warmer. I may still get myself that injector cleaner anyway
It’s the cold weather. Check any new car forum(golf, focus, bmw etc) and they will all moan about mpg in the winter on the diesels. Your using your wipers, heaters, lights also and it’s colder which means potentially more idling etc etc. My a1 diesel is only getting around 37mpg. Not much more than my 20yr old fiat which is getting closer to 30 in the colder weather.
murtgurge5 h, 31 m ago

probably that holiday weight you put on aye no but tyres can lose …probably that holiday weight you put on aye no but tyres can lose pressure in cold weather, and tyre pressure can affect efficiencyany extra weight will reduce efficiencycold weather reduces efficiency (engine has to stay warm)if you have the heater in in the car, that's not magic and will use fuel (same with AC)cold air is more dense than warm so you have more dragwhen our brains switch to "safe mode" i.e let's go 30 in this 50 area because it may be icy - efficiency is reduced



Thats the first time I've heard that using the heater in the car will use fuel, AC yes, but not the heater, I thought it was purely electric and utilising heat given off from the engine...
andynicol1 h, 21 m ago

Thats the first time I've heard that using the heater in the car will use …Thats the first time I've heard that using the heater in the car will use fuel, AC yes, but not the heater, I thought it was purely electric and utilising heat given off from the engine...


Some diesel cars have preheaters that only work when outside temp is less than 4c, basically it helps the car heat up quicker in the colder weather. Also using the engines heat to heat the car up via heater causes the cars engine to take longer to heat up. Diesel cars take a very long time to warm up and reach optimal temperature, until they reach normal temperature they're quite inefficient and will consume a lot more fuel. Lots of short journeys then the car will be inefficient and return very poor mpg. In the summer they warm up much quicker so run much more efficiently and sooner. Also you're using lights, wipers, heaters more in the colder months, along with more wind, rain, less traction etc..
Edited by: ".MUFC." 7th Jan
andynicol42 m ago

Thats the first time I've heard that using the heater in the car will use …Thats the first time I've heard that using the heater in the car will use fuel, AC yes, but not the heater, I thought it was purely electric and utilising heat given off from the engine...


likely not noticeable but it does
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