I've been running premium which seems to help a bit but shouldn't be as bad a regular as I believe premium doesn't contain ethanol. I've been using Co-op but I think I'll switch for a bit to see if that makes a difference. The big jump in decline was in November so the stations should have been pumping "winter" fuel for a while before the mileage dropped.

It literally dropped off after a fill at a Co-op in SK on my way into the province and didn't creep up until I got close to the AB border on my way home making me think it's more temperature related than fuel. I reset the mileage gauge when I fill and track mileage so I have about 3 years of trending as crazy as that sounds. I put on a storm front once I got back in December which helped keep the rad temp up but the engine was always hot regardless.

When home I park in a heated garage and don't idle for more than 3 minutes when leaving work so I typically don't notice a big difference between summer and winter. It's also been fairly warm in Calgary for the last month so I wouldn't think outdoor temp has much to do with it.

I have put the stock size back on and it still is more thirsty than it used to be. It used to level off at 15l/100km in town and now it is still 18 with the stock size. I'm assuming it's running rich but it's not throwing codes and doesn't seem to have any weird noises or quirks.

I need to figure out if how to trend with my SCT tuner to see if I can view the output of the temp sensor and O2 sensors but haven't had time to play with the data-logger.