[da-coder]

Well I decided to do a service today since I had time this afternoon.
The dealer I bought the car from stated that (paraphrasing here) "all filters were replaced" as part of their normal service.

Here is the air filter (OEM, dated 2016):

And here is the OTHER side:

Here is the MPG difference: (same mode, driving style, time of day, etc):

So that explains why the max MPG I ever got was 33 MPG.
Now it's time to check the oils, coolant, and brake fluid...

 

[da-coder]

It's worth noting that the molded date on the plastic is just the date that it was made. 2016 was the final production year for the CR-Z but they make piles and piles of extra parts during vehicle manufacture that are then set aside and stored as spare parts. Some parts may continue to be produced for a little while after final vehicle production while others will cease production after expected necessary spare part allotment is fulfilled and may only come back into production should something arise in stocking/shortage or recall. So it doesn't necessarily mean that the filter hasn't been changed since 2016. If it really hasn't been changed since then than this car has not had lot of miles put on since and or it's been operated in a region with very good air quality.

I've pulled filters from the CR-Z with ~15-20K miles on them that looked way worse than that (in a known poor air quality city). The topside of yours at least shows that it was still filtering good, but does look characteristically caked underneath, which may be responsible for some MPG degredation.

The dirtiest filter i've seen was on tractors that were run on really dusty acres. Oil bath filters were the best imo.
The only thing worth noting (which can't be seen in the photo) is how much heavier it was than the replacement OE filter.
Felt like it was packed with mud.