I'm confused with this, are there any combustion gasses in the carter and why do they need to be filtered?

What is the Carter gas filter, where is it located and what is its use? Is there a way to estimate if it is for change?

Here is a diagram showing where it is located on BMW engine: enter image description here

and here is what it looks like:

enter image description here

I really can't understand what it is for?

Gas like combustion gasses, not like benzine(gas).

1 Answer 1


(NOTE: Since you aren't talking about an ancient fuel filter, I'll change my answer ...)

This appears to be BMW's version of a PCV (Positive Crankcase Ventilation) valve. It's purpose is to pull gasses which have passed by the piston rings and into the crankcase and force them back through the intake system to be burnt. It doesn't necessarily filter the gases. Gasses left in the crank case cause several problems:

  • Fuel mixes with the oil and contaminates it.
  • These gases exhaust into the atmosphere and cause pollution.
  • Can cause carbon buildup and varnish within the crankcase area of the engine.

I am assuming this is what the part does mainly due to where the tubes run to. Most American cars use one tube which runs to the top of the engine (valve cover). Yours is shown to pull it from both the valve cover and by the dip stick tube, but performs the same function.

  • sorry about my bad English :)
    – Ziezi
    Apr 14, 2015 at 20:54
  • 1
    I got all of the points except: "force them back through the intake system to be burnt". How is this helping the combustion, increasing temperature (as combustion gasses they should be high temp), decreases oxygen?
    – Ziezi
    Apr 14, 2015 at 21:39
  • 1
    @simplicisveritatis - It has nothing to do with improving the combustion process itself or improving how the engine runs. It burns the unspent hydrocarbons so they are not released into the atmosphere. Apr 14, 2015 at 23:20

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