Mazda CX-8 Diesel Problems
Mazda CX-8 DPF issues around town?
Given the CX-8 only arrived on the market in June 2018, it's a bit too early to say conclusively, but the current CX-5 diesel (which shares its mechanicals with the CX-8) seems to be trouble free under these conditions.
Early versions of the first-generation CX-5 diesel had diesel particulate filter (DPF) issues that caused diesel fuel to leak into the engine oil, but this was fixed with hardware and software upgrades under warranty in 2012.
Having said that, any car will likely benefit from the odd highway run, but I wouldn't have any concerns about the CX-8 around town.