Two Air Filters?

Hi Clif,

If you are talking about the carbon filter located in the lid of the engine air filter housing, its purpose is to capture hydrocarbons that come up from the intake manifold when the engine is off. As Evan said, this does not require maintenance, just don't get it wet.

 

The carbon thing adsorbs gasoline VOC's. My FJ has one too, it's considered permanent

 

I bet if you trace the air passage from the intake duct you will see that the carbon comes after the replaceable filter.

 

Hi Clif,

I notice your signature block indicates that you get 52.2 mpg. My guess is that you don't achieve this via frequent full-throttle acceleration - am I correct?

Since the only point of removing the carbon filter is to potentially slightly improve air flow to the engine, at the expense of emitting more hydrocarbons into the atmosphere, it doesn't seem that this is a modification that a Prius owner would be quick to do.

If this concerns you, I suggest that you remove the housing lid, so that neither the carbon nor the paper filters are in the air flow path. Then do a full-throttle acceleration run and see whether you note any performance difference or not.

 

I love that about the Prius owners doing mods to the car. They are environmentally conscious.

When I had my Celica, people in the newcelica.org forum were removing the butterfly valve to gain a few extra hp without any regard to the emission.

 

I change my carbon filter in my home furnace every 3 months becasue it no longer removed cig smoke like a new one. I cant understand how this filter is perm and how it can somehow remove hydrocarbons for millions of miles. Its a nice trick but does nothing in the long run beside restrict air flow and collect dirt.

 

Presumably it's to keep oil and fuel vapors from escaping the engine after shut-off. They get re-emitted by that filter and burned when the engine runs. Any crud that might clog it up gets stopped by the replaceable upstream paper filter (unless someone has removed that, hoping for more "performance").

 

Just because you don't understand how it works doesn't mean it's a trick. Cig smoke is partially a particulate, and filtering particulates is different than filtering VOC. A furnace filter is also a completely different application.

The filter does not permanently collect VOC. The collected VOC is returned to the intake air and burned off during vehicle operation. This is why it does not need replacement. It's located after the main air filter in the airflow, so if it's getting dirty, your engine is too.