Hey folks, few opinions on the interwebs on this.

On the DW12 TD4, what can you tell about the condition of the engine (piston rings and amount of blowback, more specifically) if you do the oil filler cap removal test with engine running? I tried this at idle, I get a moderate amount of white smoke (white to my eyes, at least) but no change in idle speed or any other symptoms; engine has a smooth idle with or without the oil filler cap. I can add a video if useful.

Opinions valued, much obliged.

If there's no pressure, then it's fine. You can tell if there's an issue, simply by releasing the oil cap but leaving it in place. If the engine is OK, then the cap will just jiggle about on top, but won't move out of place.
These engines are generally good for 250k + miles. Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Thank you, just tried it, all good!