Oil Catch Tank Question



  • My £17 with free postage eBay bargain.
    The plan is to have the pcv and breather that goes into the induction pipe connected to the already fitted tubes. Then to drill and fit the top one to go back into the throttle body.

    What do you think, will it work?



  • Hi Jackdaw,

    Think the idea of two connections is one 'IN' one 'OUT' ?

    I wouldn't bother with the 'drill/tap' of a 3rd connection and feed back to TB!! as your kind of defeating the object of the catch tank?
    you'd still be feeding the TB and hence your combustion with oil/water vapor, diluting the ideal 14:1 fuel/air ratio? ( delete it from inlet altogether)

    Better to put a 'Y' or 'T' into 1 union from PCV/breather to the tank and run a tube from the 2nd union to a little remote air filter (K+N) high up in the engine bay (to allow drain down of condensed gases as engine cools when not running.

    Another tip is to insulate your tank feed pipes and to position the tank low and in or near a duct from the front of the car?…. the idea being that the cooler air from forward motion more readily condenses the gases from the engine and allows the fluids (oil/water) to fall out of the airflow and be 'caught' by the 'catch tank'.

    Just a thought fella :)

    kev b.



  • Right that makes a lot more sense, to take the hot oily air out of the system. Will this affect the tick over though, thought I read some where will cause the engine to die?



  • Hi fella

    Yes it could actually affect idle speed, ie idle slower? as on a system without a catch tank (standard), on idle with the throttle valve closed the vacuum created by induction will:

    A) draw metered air in via air filter through VAF and through IAC (as it should).

    B) draw in 'blow by' crankcase gases (un metered) via PCV valve (front rocker cover).

    When the throttle is opened the induction vacuum will decrease and the PCV will close and allow the two rocker cover breather pipes to then take over which feed the dirty oil laden gases into the induction upstream of the throttle valve under positive pressure, these also carry un metered air!

    It follows that if you delete these feeds to the induction, the only air entering the engine for combustion will be metered by the VAF.

    In essence fitting a catch tank you're trying to create and isolate two separate systems:

    1. Metered induction air. GOOD

    2. Dirty, hot, blow by gases laden with oil vapour and carbon deposits. BAD

    Obviously any pipe that you've routed to the catch tank, its original connection to induction will need to be blocked off!!

    Maybe? connect up your catch tank as described above and then jump TEN and GND and adjust idle speed when normal operating temp is reached so ECU can adjust to new set up :) ?

    You're spot on with engine dying on a standard K8! ie if you pull dipstick, or if you remove oil filler cap, because in effect all you're doing is opening induction to the atmosphere and breaking vaccum and hence the VAF will not meter ANY air and go crying to ECU that engine is 'OFF'!!! :(

    Bear in mind also that MAZDA may have spent millions on emissions and induction design to achieve the best balance in performance and cleanliness! altering either of these may affect drive ability or your offspring's future planet!!!! :o

    Hope this waffle helps and if you notice any difference after you plumb your catch tank in? then maybe report back with your findings to help others considering a similar conversion. :P

    kev b.


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