Can I trust that little gauge?????
Our 07 Dodge - 5.9 Cummins - has a gauge like this on the air filter The owner's manual says to depend on this gauge to tell you when to change the filter. In fact, on page 391 it says never...
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The reason is that opening the air filter box to inspect the filter can introduce dirt into the engine. It's almost impossible not to get some contamination into the air system if the filter is removed for inspection.
The appearance of an air filter is not a reliable way to judge its condition most of the time. Ironically, air filter experts have said that a brand new air filter does not filter as well as a used one. The reason is that the layer of dirt on the filter element actually helps keep additional dirt from getting into the engine. What appears to be an absolutely filthy filter may be doing a better job than when it came off the shelf. Of course, when this reaches the point of restricting air flow to the engine, it becomes a negative. The gauge is designed to indicate when this is happening.
Thus the logic of trusting your gauges, unless you have other indications to the contrary, is a well advised procedure.
The appearance of an air filter is not a reliable way to judge its condition most of the time. Ironically, air filter experts have said that a brand new air filter does not filter as well as a used one. The reason is that the layer of dirt on the filter element actually helps keep additional dirt from getting into the engine. What appears to be an absolutely filthy filter may be doing a better job than when it came off the shelf. Of course, when this reaches the point of restricting air flow to the engine, it becomes a negative. The gauge is designed to indicate when this is happening.
Thus the logic of trusting your gauges, unless you have other indications to the contrary, is a well advised procedure.
