You clean the engine air filter on a Case flagship combine once a year? Pretty impressive. Running two machines side by side I clean them every day. The 40 series stays cleaner than the 30... the 7230 gets pretty caked up with fine dust every day. I suspect a single combine running in a field would stay clean much longer. Not sure how often my cousin has to clean the engine air filters on his CRs. Every few days at least I suspect.