Hello GC1,
Replaced the air cleaner on our 350 CAT at about 22,000 miles because I thought it was clogged. The Vacuum indicator was at about three notches from the red. The drain valve at the bottom of the air cleaner was missing and I thought a lot of dust from dirt roads we travel had been sucked into the cleaner. Easy enough job to replace but turned out to be unnecessary. The new filter went immediately to 4 notches from the red. Cleaned and kept the old filter.