Fuel consumption

[Peter Michaels]

Just an update to the fuel consumption thread. In the winter I got 14 to 16 mpg. Now after fitting a new Mercedes thermostat, I get 22mpg town driving (better weather anyway) and on a 65 miles stretch constant speed of 60mph I only get 31mpg.

Mercedes manual says I should get 27 in town and 47mpg distance driving.

It's there something else I can do to improve mpg ? These figures are still quiet low.

The display shows an average of 35 town driving at about 20mph and average of 35mpg distance driving at 60mph and always stays at about 35 instead of climbing up.

That is checking consumption after filling up click to click eg.

Many thanks

 

[Joesoap17]

How many miles has it done? Service history: when was air filter/plugs last changed?
I have had 4.0l Jags with better mileage than that!
as a start I would get a good injector cleaner and give it an Italian tune up!!

 

[Peter Michaels]

How many miles has it done? Service history: when was air filter/plugs last changed?
I have had 4.0l Jags with better mileage than that!
as a start I would get a good injector cleaner and give it an Italian tune up!!

Bought a few months ago
103000 miles
Full service done 2 months ago
Full service history always from Mercedes
Starts straight away so I did not change the plugs.
Air-filter quit new looking, not changed
Done injector cleaner.

 

[Peter Michaels]

Bought a few months ago
103000 miles
Full service done 2 months ago
Full service history always from Mercedes
Starts straight away so I did not change the plugs.
Air-filter quit new looking, not changed

Buy k&n filter? Would it make any difference?

 

[esscee]

Sounds silly but are the tyre pressures correct?

 

[skippyjasper]

I'm not a proponent of K&N for street cars as the stock filter system is very good. K&N's are fine for race or off-road.
The challenge is applying the correct amount of oil to the filter. Very easy to over-oil which can contaminate the MAF.

Things that can affect mileage aside from driving conditions and what you've indicated are gas quality, MAF condition and air leaks.

Does this vehicle have O2 sensors? If so, they are due for a change out.

 

[Peter Michaels]

Sounds silly but are the tyre pressures correct?

It says 30 around and I check every week

 

[Peter Michaels]

I'm not a proponent of K&N for street cars as the stock filter system is very good. K&N's are fine for race or off-road.
The challenge is applying the correct amount of oil to the filter. Very easy to over-oil which can contaminate the MAF.

Things that can affect mileage aside from driving conditions and what you've indicated are gas quality, MAF condition and air leaks.

Does this vehicle have O2 sensors? If so, they are due for a change out.

I have to find out, but no lights come on and the idle is smooth.
I check the oil.
Gas quality is from Esso or shell

 

[skippyjasper]

Do you have the ability to scan the vehicle?

Over here it's possible to get information from a MB dealer using the VIN. I've approached the Service Department and asked to see the history. Usually cannot get a copy as it contains info on previous owner(s), but you may be able to glean relevant maintenance.

It's also useful not to wait until the car says something is amiss via the dash light.

 

[DSM10000]

Buy k&n filter? Would it make any difference?

No improvement, possibly run a little worse!

 

[Joesoap17]

I would disconnect the battery for 30 mins to reset self learn on ECU, then check over next few weeks.
Is it an auto? last ATF change?
Failing that it has to be O2 or MAF, cant think of anything else that affects fuel consumption that much--
you could disconnect MAF and see if any change? but do things one at a time.

 

[190]

Buy k&n filter? Would it make any difference?

Your MPG isn't what it should be so there is definitely something wrong. At a steady 60 you should be seeing 40 MPG so it has to be running rich, possibly the MAF or O2 sensor as already suggested.

What ever it is there is one thing you can rely on with certainty; a K&N filter will not cure it.

 

[clk320x]

Starts straight away so I did not change the plugs.

You should still change them as otherwise they will be incredibly difficult to remove later as they will seize

 

[geraldrobins]

The mpg figures sound about right to me. I think the 47 mpg is the extra urban figure which is at an average of 39mph and at ideal conditions

 

[Deletedmember130310]

Those figure seem perfectly respectable for a car of that age and mileage.

 

[Deleted member 65149]

Those figure seem perfectly respectable for a car of that age and mileage.

Doesn’t sound respectable to me. My 1999 CLK 230K would do around 40mpg at a steady 70mph over that distance. I agree with first trying the ECU reset mentioned earlier.

 

[Peter Michaels]

How many miles has it done? Service history: when was air filter/plugs last changed?
I have had 4.0l Jags with better mileage than that!
as a start I would get a good injector cleaner and give it an Italian tune up!!

Italian tune up sounds good

 

[Peter Michaels]

Hello everyone
Here is a little update. I changed sparkplugs, added k&n filter. Added Liqui Moli ceratec. gave it an Italian tune up.. sort of.. and the engine runs a bit louder, but it's morer esponsive. The general stopping starting round town is about 26mph now and I did another 50 Mile run and got 56mpg at steady 60mph. The only thing i don't like so much, is that since the k&n filter the engine can be heard whereas before it was very quiet.

Have a happy Christmas and thank you for all the help you gave me