True to a point Kit. If it becomes really dirty the vacuum will increase under the filter and it will start passing particles that would normally be trapped but that is way beyond it's time to be changed. The service interval on cars is 30,000 and most make that pretty well. I disagree with the 12,000 mile interval on the 1800 is why I haven't changed mine yet.Even the standard OEM unless you run on dirty and dusty roads a lot will still be relatively clean at 30,000 miles. I suppose it would go much further than that under normal conditions, and actually as a filter does become partly restricted with dust and debris it becomes a better filter .