Hi all, I am new to the forum.

I am a life long car enthusiast, and have recently bought my first Mercedes. It is a 1999 C220CDI 5 speed Auto Saloon with 145k miles on the clock. I got an absolute bargain

I am exceptionally happy with the car. It drives like new and is spotless inside. For the money there is nothing else out there like it.

However, I have one problem. Stated MPG is 46 combined. I didnt expect that, as you rarely get near manufacturers claimed economy. However, I am only getting 31mpg and am doing 50% motorway mileage. I dont have a heavy foot. Apparently it is not due a service for 9k more miles, and is not smokey / misfiring etc.

Could anyone maybe suggest where I might start looking for the issue? Is it simply not returning the MPG because it is older and has near to 150k on the clock? I dont want to go to a mechanic and have them re-fit scores of parts none of which actually improve things.

I dont know if it is relevant but the car makes a kind of ticking sound when accelerating.

Thanks in advance for any help

 

Welcome to Mercedes. My 2006 CD220 estate turns 30mpg around town and 40mpg on the motorway (thats imperial gallons). Interestingly I did an economy test today and believing my trip display to be reasonably accurate found :- 40mph returned 43mpg, 50mph returned 42mpg, 60mph returned 41mpg, 70mph returned 39mpg but 80mph actually returned 45mpg.
It is my belief that in order for Mercedes to get more power (at higher speeds) they have reduced the compression ratio and fitted a bigger turbo than is necessary. Now around town a low compression ratio gives a lower burn temperature in the cylinder (desirable to produce lower NOx) but returns poor fuel economy. On the motorway at 70mph the turbo is partially working but has barely raised the dynamic compression ratio back to that of a normally aspirated diesel i.e. 24:1. However when you get to 80mph the turbo is really whistling air into the engine and it becomes muck more efficient (probably achieving a dynamic compression ratio of 30+ :1) but alas the wind resistance now plays a major part. Try getting up above 75mph whenever possible and see if your economy improves. Over the last 20,000 miles my C220 is averaging 38mpg. I personally think if the cylinder head was skimmed (to increase the static compression ratio) and the turbo size REDUCED the car would not do 140mph max but it would do signficantly better mpg. Let us know how you get on at 80mph.