TDI Fuel Efficiency Has Gone Down

[dbbyleo]

I've got a 2011 Audi A3 TDI with 111K miles. I bought it with 103K miles. I've only had for less than 6 months. I bought in December and I'm in Colorado. I replaced the Fuel Filter, Air Filter, Engine Oil/Filter, and DSG immediately. I used Power Service (White Bottle). I drive 99% in the city. In the first few months of driving, I was getting mid 30's mpg. I fuel up at the same gas station and even at the same pump.

In the last 2 fuel up, I've noticed my mpg has gone done about 3-5 mpg. The only changes that I can think of that could have contributed this change is having switched from the Power Service (White Bottle) to Power Service (Grey Bottle) since we're in Spring now. I also put on a set of new tires (Falken Sincera). And since it is spring, I've actually had to use the AC for the first time... but only very, very little.

Would all/some of this be what's causing the dip in mpg?

[Audibot]

Probably the tires. I lost ~3 mpg on my TDI going from Toyo Proxes 4+ to Michelin Pilot Sport A/S 3+. The grippier Michelins are great for traction (especially in the wet) but not so much for economy.

[dbbyleo]

Yeah... I was suspecting the tires too, but the other thing I've noticed is the DPF regen (if I'm saying that correctly) is occuring more frequently now. I haven't tracked it by mileage yet, but I've noticed the the RPM slightly higher more often (when I'm at a stop)... and fan running (even on cooler day) once Ive turned off the engine. These are signs that DPF regen is occuring right? Anyway... seems to be happening more frequently. I would thing that would really hammer the economy and wondered if changing diesel additive have some effect on that?

[Audibot]

Has this happened for more than one fill-up? I am wondering if you got some bad diesel or something. You can try swapping back to a tank of the white bottle to see if it changes back

[dbbyleo]

Yes... this has happened to the last 4 fill ups at least.
Yeah, I thought about trying to test running with PS white bottle and see.

[Coolrunning]

Have you been giving it a good Italian tune-up once a day or so? Driving with it above 3k RPM’s for like 10-15 minutes to burn and clear everything out helps a lot. Probably not 3mpg’s worth but can’t hurt.

[Silicon Voodoo]

you Americans (and by way of cultural influence reach, Japan also) speak in reverse units, MPG is a hyberbolic relation (1/x); so losing 3-5ΔMPG from 30MPG is not the same as losing 3-5ΔMPG from 15MPG.
You went from 7.8L/100km to 9L/100km.
in the hypothetical 15 to 11 that'd be 15.6L/100 to 21L/100
just saying that for non-imperial natives ppl on the forum who'd like to get an idea of what's going on.

[Coolrunning]

you Americans (and by way of cultural influence reach, Japan also) speak in reverse units, MPG is a hyberbolic relation (1/x); so losing 3-5ΔMPG from 30MPG is not the same as losing 3-5ΔMPG from 15MPG.
You went from 7.8L/100km to 9L/100km.
in the hypothetical 15 to 11 that'd be 15.6L/100 to 21L/100
just saying that for non-imperial natives ppl on the forum who'd like to get an idea of what's going on.

I don't want a large Farva. I want a god damn liter-a-cola! [:D]