[kamona]

Hi, my N52B25 is consuming 1 liter of oil in about 700-1000km. I have replaced the PCV unit but it had no effect. If I drive shortly and let the car sit for maybe an hour or so, it sometimes makes a rather big cloud of smoke. It doesn't always smoke on startups, but sometimes a little.

Looking at the pistons with a borescope camera all have some carbon buildup, but one seemed wet of oil.

To me the intake valves looks reasonably clean, with some colouring. Is it possible that only the exhaust valve stem seals are causing this? Or is it likely that it is a piston ring issue?

[NZE90]

What year is the car? They did have oil control rings issues but this was corrected in later production models.

[gaze2]

I am in the same position as you, early magnesium cover n52b25, 400k km on the car, burning 1 liter ~1000km atm
Intakes looked clean in my opinion, however after seeing yours I can say they are pretty dirty, with gunk around the valve guides.
Changed PCV, used to burn 1 liter every 400-500km
Changed spark plugs, they were all covered with this white mineral thing (row 2, 1st pic but worse), none of them were wet like that one you have (last row 1st pic). Don't have borescope, so didn't check inside.
I am pretty sure I am affected both by the pistol oil control rings thing issue and valve stems leaking. When I would coast with little to no throttle and then floor it, engine chokes a bit and smokes. Or for example if I drive/coast slowly to my parking lot, and then when I reverse in a spot I enter my own smoke cover. Otherwise no smoke on start up (on warm start revs jump to 1500-2000 and instantly go back down), if I idle for 10-15 minutes and then floor it, no excessive smoke. I have all my cats.
I will upload pictures when I get home from work.

My plan is to try to use the Liquimoly engine flush next oil change, as there is quite a lot of gunk under the valve cover. I do not plan to change valve stems nor open engine to fix piston rings. Swapping to an N52B30 seems the better option.

[kamona]

Originally Posted by NZE90

What year is the car? They did have oil control rings issues but this was corrected in later production models.

This is a 2005 so could very well be the oil control rings. Would it help to do a piston soak?

[NZE90]

A piston soak?

[mictang]

At this age and mileage, you likely have both valve seal and oil ring issues.

My 2007 325i came stock with the B25, exhaust valve stem seals were leaking pretty bad, very easy to tell, heavy black gunk build up literally dripping out of the valve guides. Intake is washed by fuel so it won’t be easy to tell.

Liqui Moly Oil Saver can be pretty effective on worn seals alone.


That being said, anything before ~2010 will have the piston/oil ring designs that are known to burn oil (this is B25 specific).

At around 250K km, my original engine's cylinder 6 lost compression almost entirely and I confirmed it was ring issue as adding oil brings back some compression. Other cylinders were still good. I was burning 1L maybe every 2000-3000km at the time (with Oil Saver, 40 weight oil).


In your case, I would do a compression test/borescope the cylinders first. If it's bad/has noticeable scoring, you are looking at either a rebuild or engine swap. Best case scenario, you can get away with piston and ring replacement, which is a relatively common (but still major) repair for the B25. I ended up getting a B30, mechanically it's plug and play, ECU flash is needed for full function but you can start and run the car on B25 tune.

If you have good compression, then Oil Saver will reduce valve seal consumption noticeably, and flush might have limited success on oil rings. The oil rings are on the crank side so piston soak might be less effective, worth a try though.