W212 MPG lowered after spark plug replacement
 

I have a 2011 E350 sedan with 105K miles. I did a service B on it and replaced the spark plugs. I used Bosch YR7MPP33 plugs which are OEM for my car. I noticed that the mpg went down instead of up as expected. I was averaging 21.5 mpg with old plugs and now am getting 15.5 mpg. Only have been running with new plugs for a day. Is this normal? What could cause this problem? The car drives very good, It actually feel a bit smoother and picks up faster. I torqued the plugs to 16 ft-lbs..

Had the same issue , with bosch , changed to NGK and all became good.
maybe there were other factors involved but yeah
torqued them to about 20nm i think it was

How did you determine 6 mpg drop in one day of use? That seems like a huge decrease.

I know that Bosch and NGK are used by MB and I've seen other posts relating to mpg. In my case I changed oem Bosch for same and gained almost a couple of mpg.

the mpg is displayed immediately while your driving on a E350. It's always been spot on. I will change to the NGK and see if it fixes the problem.

Will be interesting to see results. I think the oem NGK plugs are Laser Platinum PLKR7A.

Bosch and ngk
https://cimg0.ibsrv.net/gimg/www.mbw...dd1504f420.jpg
https://cimg1.ibsrv.net/gimg/www.mbw...c52885901e.jpg

See attachment.