Oil consumption
Maximum oil consumption
Beyond the rates above, the owner needs to take action. Leaving the engine excessively burning oil will inevitably result in semi-clogged or fully clogged catalytic converters, depending on the burning rate.
In worse cases, misfires, cylinder compression loss, cylinder bore scoring and fatal pre-ignition if the rate reaches its stage 3.- Stage 1: 1L/4000kms
- Stage 2: 1L/2500kms
- Stage 3: 1L/10000kms
Excessive Oil consumption in a NA engine.
Piston / Piston Rings
1Worn Piston Oil rings.
All N52b25 prior to June 2010, have faulty pistons with mal-positioned oil drain holes plus low-tension oil rings which are designed for chamber high-lubrication. Click here to Read the corresponding service bulletin (SIB)Facts
- While the N52b30 pistons were made by Mahle (CR 10.7:1), The faulty N52b25 pistons were made by KolbenSchmidt (CR 11.0:1).
- BMW in its SIB claims the position of oil drain holes is unfavourable especially when the engine sees lots of short drives and start/stop events. But does not indicate what happens technically (Clogged oil drain holes? Gunked oil rings? or Both?)
- Experience shows that the N52b25 due to its higher compression ratio, is very sensitive to gasoline quality. It was designed to run optimally with RON100 fuel. Repetitive usage of dry RON95 (Bare minimum of legal additives), short trips, excessive idling, lack of spiritied driving (High engine RPMs), makes for a fast clogged piston oil control ring and drain holes.
- The piston design of the N52b25 is inherited from the BMW N42 piston (Made by KolbenSchmidt and has also 4 oil drain holes offset on the skirt side)
- An academic study from 2018 proved that the optimal number of piston drain holes is 4 and their optimal position is on the skirt side. This is what we do see on the upgraded 2020 Mahle piston made for BMW B58 engine. What the study missed is that this is only the case when the operating conditions are favorable. In real world cases, oil drain holes on the skirt side get easily clogged by carbon/deposits. This is exactly the case of Toyota 2006-2009 2.4L petrol engine 2AZ-FE. This engine with oil drain holes on the skirt side, suffered from oil burning issues after a certain mileage. Toyota fixed the issue by moving the holes to the wrist pin side and many users by drilling two additional holes on the wrist pin side on old pistons when rebuilding the engine.
N52b25 old version piston over-sludged oil control ring.
N52 piston clogged oil control ring.
N52 piston over-sludged rings.
N52b25 old version piston coked piston crown caused by excessive oil burning.
N52b25 old version piston vs updated piston (Re-positioned oil drain holes).
N52b25 old version piston vs updated piston (Re-positioned oil drain holes).
N52b25 with sludged oil control rings and piston drain holes requires fully-synthetic premium oil. Amongst High-Ester (Diester, Lanolin, Polyol, Synthetic faty acid Esters ...) synthetic passenger car engine oils produced by brands like HPL, Redline, Ravenol, Valvoline... Rule of a thumb, the greater the amount of Ester in an oil, the more expensive it will be. They tend to have a high value of Oxidation values revealed by VOAs, outsdanding low NOACK (Evaporation loss ratio) values and suprisingly a VI (Viscosity index) that falls below 170, (Very low amount of viscosity improvers). This type of oil through short OCIs beside its ability to help swell valve stem seals, should be able to clean the carbon deposits on piston ring lands (The carbon molecules are softened/broken then dispersed in the form of liquid to be trapped by the oil filter), slowly but effectively as long as the fuel used is toptier additived RON95/RON98/RON100 gasoline, fuel treatment with high PEA cleaner is periodically used (Every 3 or 4 tank fillups) and short-trips/idling are minimal/avoided. Some of these oils that have made their reputation are:
Some of the best high PEA fuel system cleaners are:In case of semi-stuck piston rings or partially-clogged drain holes because of heavy carbon deposits (Not critically worn rings), A faster and more effective approach (Boutique oil additive cleaner) can be performed:
HPL EC30- Two 3000 kms oil changes using HPL EC30 (1 liter per 5L of 5W30 Shell HU ECT C3 oil or any BMW LL04 Group III GTL based oil. Best for avoiding conflict of different types of Esters)
- At least four 5000 Kms oil changes with HPL PCMO Euro 5W30
- Few hundreds of kilometers before each oil change, run one of the PEA fuel cleaners mentioned above
- Hot Shot Secret Stiction Eliminator is specially made to remove the hard carbon produced by burnt oil. The treatment usage for the N52 consists of a dose of 500ml poured into 6 liters of oil.
- At least four 5000 Kms oil changes with HPL PCMO Euro 5W30
- Few hundreds of kilometers before each oil change, run one of the PEA fuel cleaners mentioned above
- Xenum M-Flush A boutique engine cleaner. Is solvent-free, seals-safe and does not destroy the oil protective film. One bottle for 100km should dissolve a good amount of piston carbon
- At least four 5000 Kms oil changes with HPL PCMO Euro 5W30
- Few hundreds of kilometers before each oil change, run one of the PEA fuel cleaners mentioned above
- Auto RX Plus is based on Laninol esters and is designed to safely break piston deposits.
- 1 or 2 bottles blended with a GTL based oil. Preferebally Shell HU.
- At least one 5000 Kms OCI with the cleaner
In case of completely stuck piston rings, a correctly performed piston soak method can drive the oil consumption down by at least 3 or 4 times (This method can be repeated 2 or 3 times to get satisfactory results). It is based on using a highly concentrated fuel system and uper cylinder cleaner. Products that proved to be extremely effective are:
- AcDelco FSC and UC cleaner X66P 88861803 (GM endorsed but very Hard to get)
- BG 44K (GM endorsed)
- Redline SI-1
- Chemtool BerryMan B12
- Use Berryman Chemtool B12 as the cleaning substance (~ 60ml per cylinder).
- Cover the spark plugs wells with towels and let B12 soak for at least 20 hours before turning the crank manually or using the starter
- Pour more B12 onto the cylinders and wait at least 8 hours before cranking manually 4/5 times or with the starter
- Pour more B12, wait at least 4 hours and crank again few times. Ideally use a tube similar to XADO Red Anticarbon
- If using the starter, it is a good idea to plug a battery maintainer/charger to avoid battery discharge
- When done, it is mandatory to make sure you vacuum out remainders of B12 and broken carbon chunks from the cylinders. Use a powerful device.
- Vacuum out any left B12 from the the top of the catalytic converters eventually, through the upstream O2 sensors holes
- Change the oil and eventually the filter (Make sure to prefill the filter)
- Pour a tiny amount of thin oil (~ 50ml) through the spark plug wells, and turn the crank manually 3 or 4 times. Use a long thin spray tube to be able to reach all edges. This is to avoid the engine starts on dry cylinder walls and piston rings.
- Vacuum out the excess oil from each cylinder, before starting the engine
- The engine may start with difficulty the first time and run rough with gray smoke from the tailpipe. Let it idle for 10~15 minutes before driving. First drive trip should be gentle.
- TIP 1: Since the engine is angled in longitudinal position, jacking the car on the front right side, would help the B12 substance to be distributed evenly around the piston crown
- TIP 2: To make sure no cylinder wall scoring occurs, put Liqui Moly Ceratec into the oil, 300/500 kms before starting the soaking operation. CeraTec will form a protective solid ceramic film on engine internals.
- TIP 3: If possible, measure compression in every cylinder before starting the soaking procedure and inspect each one of them using a borescope camera.
- TIP 4: Ideally change the oil twice before going for an italian tuneup to clear catalytic converter and break-in any unstuck piston ring
Once the piston soak procedure is finished, the driver must continue using one of the oils mentioned above.
For curiosity, BC B12 composition is as follows
- Toluene (40-50%)
- Acetone (20-30%)
- Methanol (20-30%)
- 2-Butoxyethanol (5%)
- Methyl Ethyl Ketone (MEK) (less than 5%)
- Isopropyl Alcohol (less than 5%)
Let us note that the N52b25 that came with Low Compression pistons (S858A) (9.7:1 instead of 10.7:1 or 11.0:1) was not affected by the oil consumption:
N52b25 low compression engine piston ( S858A). (This piston was not affected by the oil burning issue as the oil drain holes were correctly positioned).
N52b25 low compression engine piston. (This piston was not affected by the oil burning issue as the oil drain holes were correctly positioned).
Cooling system
3Malfunctioning cooling system causing the engine to run very hot and thus the oil to thin out
.Climate
3Hot climate regions like middle-east
.Driving style
2Short journeys
Frequent spirited drivesValve seals
1Worn Valve Stem Seals (Oil seeps into the combustion chamber, past the valve seals, and gets burned).
N52 exhaust valve seals prior to mid-2006.Crankcase Ventilation System
1Stuck open/close CCV system
CCV Diaphragm and/or CCV hosesLow Oil quality
2Oil incorrect grade and specifications
Very long oil service intervalsSevere oil pan leak
3.
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