CLA 220D Sporadic Poor Fuel Economy

[Spasmcasm]

Hi Everyone,
I've recently acquired a 2022 CLA 220D with 18k on the clock, I've since added @2k.
I've found that sporadically, probably every dozen commutes (Usually 15miles) my fuel economy plummets from the normal 57ish mpg down to 29-36 mpg.
When the commute ends, the fan's going ten to the dozen and the engine area just smells hot with noticeable heat coming from the wheel areas.
Steering isn't pulling so unlikely to be brakes binding. No obvious warning lights etc.
Sytner have had the car back and said nothing wrong.
Next commute is normal with fuel eco back to normal. I'm running the car in comfort mode, haven't used any other apart from eco on a 250 mile journey to see if there was any difference.
Any ideas?
TIA

Phill

 

[Blobcat]

Hello and welcome,

DPF doing a regeneration

 

[fabes]

And not completing it....

18k on a 22 reg car is good mileage and the DPF will have got upto temp and got cleaner, but your short(er) journeys aren't enabling it to cycle and regen fully.

If the dealer cannot find a mechanical or systems fault, this will be it.

 

[Spasmcasm]

Thanks Guys

 

[onefortheroad]

Tick over on my GLC goes to 800 rpm when it's trying to regen. 500 rpm normally.

 

[Srdl]

Welcome - quite normal. It's when the DPF (Diesel Particulate Filter) stops regenerating that you have a problem.