Originally Posted By: Jim Allen
Originally Posted By: mr_diy
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I previously had neglected to change an original air filter (~80k) and after running a OA and getting a rather high silicon reading, I changed it out and the next OA had one third the silicon level. That original filter did not look bad, so maybe it was channeling.
Possibly. Other possibilities are a poor fit in the housing (maybe from being removed a few times). It might have been cleaned at some point and damaged. It's also possible the filter you replaced it with is more efficient.
Most likely iIMO is just the variables of comparing only two UOAs. Unless the differences were significant (say over 25%) it could be simple testing variables. Comparing two tests does not result in very accurate comparisons. To "see" small differences, you need trending. Lots of UOAs in each condition.
I don't believe I ever removed filter prior to the change, and it still looked fairly clean when replaced. The SI dropped from 21 to 7 and the replacement filter was a Purolator classic.
Civic OA
My advice if you are not doing regular OA's, is just change based on recommended schedule. Then is the filter or gasket is failing you get it replaced sooner than later. A restriction gauge would only seem to make sense for very dusty areas where filters fill up faster than normal. Would not warn of a small bypass or failing media.