Why am I suddenly in the low 30's mpg when about 6 months ago I couldn't get less than 45mpg?

[SharkeyWard]

Not sure if this has been covered prior but my 2011 E220 2.2 diesel ah suddenly found a new appetite for diesel as i can't get above 40mpg. Last year it was doing a minimum of 45mpg (even when really pushing it hard) and regularly got over 50mpg but somehow it won't do over 40 mpg even when tickling the throttle. Any ideas?

 

[DSM10000]

It's winter. The cold temperatures affect diesel engines more than petrol.

You will also be using the heater (possibly heated seats), lights etc more and these extra demands on the alternator all add up to increased fuel usage.

Diesels are thernodynanically more efficient than petrol engines and therefore take longer to warm up, especially in the colder times of the year.

I assume you have checked your tyre pressures and have ruled out binding brakes etc?

 

[MrGreedy]

Have you had a service at a Mercedes Benz main dealer in the time inbetween? If you, you will have had an emissions software update to reduce NOx at the significant expense of diesel consumption.

 

[W1ghty]

Have you had a service at a Mercedes Benz main dealer in the time inbetween? If you, you will have had an emissions software update to reduce NOx at the significant expense of diesel consumption.

That was going to be my question as well buddy ?

 

[Bobby Dazzler]

When I read the OP my first thought was "Winter" and my second thought was "NOx update". Seems like I was not alone.

 

[clk320x]

Have you had a service at a Mercedes Benz main dealer in the time inbetween? If you, you will have had an emissions software update to reduce NOx at the significant expense of diesel consumption.

This was my first thought too...

 

[James Copeland]

Dirty air filter?

 

[SharkeyWard]

It's winter. The cold temperatures affect diesel engines more than petrol.

You will also be using the heater (possibly heated seats), lights etc more and these extra demands on the alternator all add up to increased fuel usage.

Diesels are thernodynanically more efficient than petrol engines and therefore take longer to warm up, especially in the colder times of the year.

I assume you have checked your tyre pressures and have ruled out binding brakes etc?

Thanks, I would love to believe its just the winter cold but I have a feeling it may be more especially as its my 5th year with this car and I've never had it below the 45mpg (in the depth of winter and giving it a proper work out up the lanes). Everything seems good - tyre pressures, no binding brakes etc... no worries - just though someone may have had the same thing. Appreciate the response though and well fingers crossed it may return the mpg i'm used too..

 

[SharkeyWard]

Have you had a service at a Mercedes Benz main dealer in the time inbetween? If you, you will have had an emissions software update to reduce NOx at the significant expense of diesel consumption.

Nope not had that done yet. I'll try the simple things like the air filter and see what happens - I'll let you know how I get on and hopefully find a cause (if there is a problem of course)... just odd that it's suddenly started without warning as such - one day was doing well over 45mpg the next couldn't get it over 35mpg?? I began to wonder (along with many things) as to whether the turbo waste gate wasn't closing - but the car doesn't seem down on power??!!

 

[pmcgsmurf]

Check thermostat and that car is getting up to temperature correctly, if it isn't it will burn more fuel at the lower temperature.

 

[T5R+]

HAT-TRICK for me.......

• NOx update start of last month
• Winter Tyres fitted
• Cold weather

approx 10MPG infereior according to the OBC.

 

[Tezz]

Check thermostat and that car is getting up to temperature correctly, if it isn't it will burn more fuel at the lower temperature.

My thermostat is faulty, burns quite a bit more in winter

 

[Deleted member 65149]

HAT-TRICK for me.......

• NOx update start of last month
• Winter Tyres fitted
• Cold weather

approx 10MPG infereior according to the OBC.

My OBC has a mind of its own. Often the three means of displaying mpg (average trip and instant in main display and bar chart 5 minute averages on Comand) present vastly different results. I can be cruising along a motorway with the instant reading hovering steadily around 40mpg whilst the bar chart shows 25mpg. I’ve given up looking at them now - far too depressing.