S211 E220cdi temp/mpg issue??

[Sharville79]

Hello All,

I'm trying to establish if I have a problem with my 2008 S211 E220cdi 5g Auto.

The trip computer is showing 40-41mpg on my daily 60 mile commute which is mostly duel carriageway.
I have previously owned a 2002 S210 E320cdi auto which achieved better MPG on long runs.

The car has done 72000 and I have owned it about 2 months.

The tyre pressures are correct (top level) and the boot is empty. I am in the process of doing a brim to brim mpg test.

Research has led me to suspect the thermostat might be faulty. It seems to sit at under 80c most of the time and will only rise temporarily above when I accelerate hard.

I will try and attach a photo of the cars normal temp.

Any advice or opinions would be greatly received.

 

[merc85]

Should sit under the next line above the 80 more like 89

 

[V12]

Definitely change it.

 

[Blowpipe]

Lucky if I get 40-60 degrees showing, and that was today after a run down from Leeds to Surrey. Got a new thermostat sitting in the boot of the car, we'll see what happens when that's fitted.

That said, I do see a regular 48 − 55mpg if I'm careful.

 

[Sharville79]

Thanks for your replies guys. I will definitely change the thermostat and will report back with the results.

 

[Sharville79]

Quick update: E220cdi brim to brim test showed a very disappointing average of 34mpg!! Something is definitely wrong.
The on board computer is showing 36.9mpg, so it is over optimistic.

The car is under warranty and booked into the garage for next Monday.

 

[V12]

Is that after changing the thermostat?!

 

[Troon]

The car is under warranty and booked into the garage for next Monday.

Is that after changing the thermostat?!

I'm guessing the garage visit is to change it.

I did mine (it's a very easy job, <½hr, genuine part £49) at 105700 miles which moved the temperature from <70°C to a rock-steady 90°C. Economy did not significantly change. I average 41mpg OBC across all types of driving.

If you're doing any significant amount of stop-start heavy traffic, economy will plummet.

Other data points: steady 110km/h on French autoroute 5-up fully laden with tailwind got 51mpg; really careful hypermiling drive to work got this:

but a heavy-traffic drive home can see mid-30s.

 

[Sharville79]

I don't think I do a lot of stop start driving as I live in a semi rural area.
While I don't expect miracles with such a big car I'm sure my mpg should be better.
Like I said in my original post my old S210 320cdi seemed to return better figures.

While its under warranty I might as well investigate it.

 

[l5foye]

I think you will find that newer cars do less mpg than older ones. My friend's 02 C220 CDI returns mpg that the new ones can never achieve.

 

[V12]

Emission regulations have killed the development of the cdi engines for the last 10 years.

 

[Dieselman]

Adding weight and additional power to cars has had the greatest effect.

 

[Sharville79]

Update:


All sorted, it was indeed the thermostat.
Changed under warranty and the car is now returning around 50mpg on a run.