Poor MPG from a 55 CLK220 CDI Sports

[balib_72]

Evening ALL

I was rather disappointed with the returned Miles Per Gallon on my 55 plate CLK220 CDI sports MERC.
(i)Southampton to Derby @
160 miles, 90% motorway miles driving at cruise control 70 MPH constant, no A/C and driving smoothly. I returned 38 MPG MAX.
(ii) Derby to Wolverhampton @ 70 MILES, 90% motorway miles MAX attained was 36.8 MPG.
(iii) Wolverhampton to Southampton @ 180 MILES, 90% Motorway I got 38MPG max on the trip computer.

All MPGs were recorded by the trip computer, when ever possible I used the cruise control to limit the speed to 70-75MPH, no fast accelaration was used and the A/C was off and all windows closed.

I am rather disappointed with the MPG attained, would welcome positive posts on what I can do to get better MPG.

Thanks

 

[redbaron]

what wheels and tyres non original 18" or 19" by any chance?

what tyre pressures?

what brand of fuel?

when was the car last serviced?