CLK 270CDI diesel consumtpiom reduced from 45/mpg to 23 mpg after MOT done

[bchasqueira]

Hi everyone,

Wondering if you would have come across similar scenario:

My consumption of my 270 cdi has been always really good, with most time computer showing an average 45mpg.
I just recently had my MOT done and it passed with flying colors, no advisories.

But since then, my computer seems to show average consumption of 20/23mpg consumption, which is half of what it used to.

Could something they done at MOT testing, affected my Mercedes consumption?
Any thoughts/knowledge is much appreciated.

Thanks

 

[whitenemesis]

Perhaps they reset the trip computer? Running average is starting again and you need to get some long journeys done to bring ave back up?

 

[PobodY]

Does the trip computer factor how far the car travels? - It doesn't go very far during an MOT test, but they still need to run it up to temperature so it's spent time burning fuel without any miles?

 

[wu56Shoozz]

And there you have it... its displaying a reading combined with your short journey and heavy idling.. like the previous poster says, you need some long journeys for it to return back to what its usually displaying.. mine will do this too if I sit in the driveway idling.. the mileage display will drop, but once used on a reasonable journey will start to return a healthy figure and I'm a 320CDi by the way....

 

[190]

Do they still do the diesel smoke test at high engine revs ? That would use up some fuel.

I had the MOT done on my petrol W204 recently and whatever they did it wrecked my MPG average but only on temporary basis. Once reset at the next tank fill it was fine.

 

[DSM10000]

Re-set the trip computer and also, more importantly, carry out a brim to brim fuel consumption measurement for accuracy.

 

[DSM10000]

Do they still do the diesel smoke test at high engine revs ? That would use up some fuel.

I had the MOT done on my petrol W204 recently and whatever they did it wrecked my MPG average but only on temporary basis. Once reset at the next tank fill it was fine.

So nothing was "wrecked" it just denotes fuel burnt whilst the car was stationary for the MOT.

Engine running but not driving = 0mpg!

 

[190]

No nothing was wrecked other than the MPG figure.

I realised that the MOT emissions test uses fuel and would inevitably reduce the MPG. It was how much it reduced that was a surprise. A diesel will presumably use even more fuel because during the smoke test the engine is taken to maximum revs for 30 secs which is not the case for a petrol.

 

[ashenfie]

No nothing was wrecked other than the MPG figure.

I realised that the MOT emissions test uses fuel and would inevitably reduce the MPG. It was how much it reduced that was a surprise. A diesel will presumably use even more fuel because during the smoke test the engine is taken to maximum revs for 30 secs which is not the case for a petrol.

Emmission test require a hot engine, your never sure how long they left your car running before testing it.