I have had a few trucks with this little cylindrical clear plastic indicator with a multi-colored piston inside. It is located between the air filter and the throttle body in the air intake tract. The piston within the clear cylinder shows green with a good filter, and with a blocked filter, the air flow restriction creates enough vacuum to pull the piston into the red zone (if that makes sense) indicating the need for a filter change.
I have never had a filter get bunged up enough to cause the indicator piston to move into the red zone, however before that happened, UOA's showed it was time for a filter change. When this happened, the filter actually looked pretty good.
Has anyone ever seen one of these go into the red, or are they just useless indicators (with the exception of extreme blockage situations)?
My guess is you're going to see driveability issues to accompany any red indication.
I have never had a filter get bunged up enough to cause the indicator piston to move into the red zone, however before that happened, UOA's showed it was time for a filter change. When this happened, the filter actually looked pretty good.
Has anyone ever seen one of these go into the red, or are they just useless indicators (with the exception of extreme blockage situations)?
My guess is you're going to see driveability issues to accompany any red indication.