DIY Solution to M54-M52TU CCV problems

[cn90]

I am trying to figure why this mod (more vacuum in crankcase) reduces oil consumption, and I think I have the answer (any engineers in forum?).

Quick review on 4-cycle engine: Intake, Compression, Power (Explosion), Exhaust.

- Compression, Power strokes have positive pressure inside the chamber (thousands of psi), creating blow-by.
- Exhaust is kind of neutral, maybe hundreds of psi or close to 0.
- It is the Intake phase that creates suction in the combustion chamber (thus the vacuum in the Intake Manifold).

My 1998 528i M52 has no oil consumption, even at 165K miles.
My 2006 X5 M54 has brand-new CCV and drinks about 1qt/500 miles. From reading mlody post and blog (aka ElbowGrease on youtube channel), the oil ring (the bottom ring) is low-tension and has a gap of 2.5mm after some 120K miles. This gap allows oil to sneak up and sucked into the chamber during intake stroke.

- My X5 Stock brand-new CCV: when removing oil cap, there is a slight hiss but no big deal, so the vacuum is not much.
- My X5 AFTER CCV Mod: when removing oil cap, there is a moderate hiss, so the vacuum is more than stock.


When the M54 is new, the gap is small (? 0.4mm), so virtually no oil sucked into chamber.
As mileage adds up, this low-tension ring wears out, creating the gap of 2.5 mm.

Anyway, the work around CCV mod that increases crankcase vacuum reduces oil consumption.

So, this is my theory, feel free to correct me. Numbers are arbitrary strictly for discussion...

1- Stock CCV: there is not enough vacuum in crankcase (neg 16 in Hg and neg 4 in Hg = difference of 12 in Hg), during Intake stroke, the differential in vacuum allows oil to be sucked into the combustion chamber ---> oil burned.

2. CCV Mod: now there is more vacuum in crankcase, close to I.M. vacuum (neg 16 in Hg and neg 12 in Hg = difference of 4 in Hg), during Intake stroke, the differential in vacuum is not enough to drive oil into the combustion chamber ---> very little or no oil burned.

Anyway, just a theory and would love to hear from some engineer gurus out there.

- First photo is the principle of 4-cycle engine.
- Second photo is Stock vs CCV Mod.



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