C200CDI Fuel Economy

[Seanus]

Hi All,

This is my first post here.

I've just traded in my 02 plate C200 Kompressor Coupe for a 55 plate C200 CDI coupe.

I'm getting around 38-40+ mpg generally, which is pretty much what I was expecting, but at motorway speed (constant 70mph on cruise control) I'm only getting 44 mpg. Even a steady 60 mph doesn't improve things. Surely this can't be right? I was expecting 50+ mpg.

Were my expectations unrealistic, or is something amiss?

The car has just been serviced by the main dealer I bought it from, covered only 20,000 miles and looks and drives as new.

Any ideas?

S

 

[djb]

I take it your figs are from the dash display. I have a c 200cdi auto on 53 plate and although it displays between 48- 50 mpg on the computer, in reality it means between 42-45 on real calculated figs from filling reciepts. at present the display shows 46.6 over 6500 miles, the vast majority being single mway journeys between midlands and the south, driven at 75- 85 MPH, fuel reciepts show 44 at the moment. (using a scooter at home so no uneconomic town figures in this milage)

I would not expect your engine to be quite as good as this as it will be a euro 4 build and these are by definition less economic to meet the emission requirements. Reduction in Nox is achieved by lowering the combustion temprature, which leads to lower efficiency.

For more details on this take a look at the battle between MAN, who are using EGR (Exhaust Gas Recirculation) and the others DAF, MB , VOLVO who use SCR (stratified catilitic reduction to meet euro 4 and 5 on trucks. SCR involves the injection of ad blue a urea & water mixture into the exhaust after the engine + a cat in the exhaust box. expensive, but the engine it self can go back towards euro 1 which was more fuel efficient.

 

[Seanus]

Thanks DJB, that's interesting.
I didn't know that the display (which is where I was taking the readings from) was so inaccurate.
And I guess that only the EU could come up with an eco-law that actually reduces efficiency and economy.

Even so, I would still expect the display to indicate a higher MPG at a steady 60-70 mph than standard stop-start driving.

S

 

[djb]

fuel eco

Firstly do you have a manual or auto?

as an example wife runs a polo gtdi, obviously manual, if driven economically IE early changes , look and drift throttle off, little brake judge traffic etc, it is quite possible to get its display to show in excess of 50mpg, however at 75 it will show 45mpg.

my c200 cdi will show the 48 - 50 but it takes hours to get up there, ie after 1.5 hours of driving, with only a few lanes to start.

The real figures are the calculated tankfuls, adding each on to the last , not averaging the individual results.

Another good trick is to drive at least 1 hour on m way and stop at services, with the minimum amount of use of the brake.



Then feel all tyres, this will give a good idea for wheel miss alignment as extra degree of toe in or out will noticeably heat the front tyres.

at same time gingerly touch the discs , which should be cold (if min break was used. IE the last few feet to stop.)

apology if I Am telling you something you knew about.

 

[Seanus]

It's an Auto.

The way I've been checking the MPG on a motorway is to get the car up to speed (by which time the engine is warm and everything is running normally), switch on the cruise control and wait for a flat stretch of road. Then I reset the trip computer, while on the move.

In my Kompressor, doing this would instantly register around 36-38 mpg, which was the best I could squeeze out of it under any circumstances (other than coasting down a long gradient ), and a fair bit higher than the all-time average of 31 mpg (indicated). Which is why I thought it was strange that I wasn't getting a similar result in my CDI.

I got a courtesy call from the salesman at the dealership this afternoon, and I mentioned this to him. He agreed that I should be seeing 50+ under these circumstances, so I said that I'd give it another week and if it was still the same, I'd take it back to them and let them run some diagnostics.

A manual calculation is suggesting around 40 mpg overall, which as I said earlier, is about what I was expecting.

I might give your motorway test a go this week, if I can find the time...

S