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, Mobil 1 ... Rule of a thumb, the greater the amount of Ester in a given 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 true VI (Viscosity index) that generally falls below 170, (Very low amount of viscosity improvers if not none, thus no viscosity breakdown at high temperatures and constant loads).

Those with outstanding cleaning properties are usually based on a blend of Esters with Alkylated Naphthalenes (ANs)

This type of oil through short OCIs beside its ability to help rejunevate 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. The cleaning property of Ester/ANs must not be confused with detergents responsible for neutralizing acid, usually based on Calcium/Magnesium. It is also interesting to note that oils that are more resistant to causing piston high temperature oxidation are those with high Flash Point values, generally greater than 240 (Not a general rule). The second type of cleaning oils is premium fully synthetic PCMO blended with a proprietary active cleaning molecule/agent. Some of these oils that have made their reputation are:

• Valvoline Restore and Protect 5W30 & 5W40 (BMW LL04) The HTHS is 3.5 for both viscosities. Let's note that the US version is not ACEA C3 compliant and has a HTHS of 3.26 which is still greater than the HTHS specification of BMW LL01-FE: 3.0 as well as BMW LL12-FE: 2.9 - and a viscosity of 10.8cst at 100°C, greater than the BMW LL01-FE specification (In May 2017 BMW released a document making BMW LL01FE a supersession to BMW LL01 for N52k and N52T). For example, Ravenol FES 0W30 is approved for BMW LL12-FE and ILSAC-GF6 (Valvoline R&P US approval). In conclusion even the US version of Valvoline R&P can be used on a N52 engine as long as the oil drain intervals are reduced to 3000 Kms, the oil filter (BMW Filter or MANN Filter) monitored/changed every 1000 kms and the car is driven gently (No Spirited driving). Top tier gasoline is mandatory. The two first OCIs will see very slight improvement if not a slight increase in oil consumption. It is usually at the end of the third OCI (~ 10K Kms - 15K Kms) that significant results are observed. This oil should also clean the internals of the HVA tappets reducing the infamous lifter tick. Valvoline RP presumably does not use a similar patented blend of PAO, Polyol Esters and Alkylated Naphthalenes, as their Former Premium Blue Restore oil but a proprietary molecule that cannot be revealed by ordinary oil analysis yet. Information yet to be confirmed in the future. The BMW LL04 version of Valvoline R&P can be purchased across different european dealers like Opie Oils in UK and AutoAZ in Hungary (Unix Auto) or RacingLubes.fr in France.
• Mobil 1 Advanced Clean AFSMO (Similar to Valvoline RP, but not yet enough user feedback on whether it is achieves the same results)
• Mobil 1 FS ECF 0W40 (BMW LL01). With FS 0W40 that delivers outstanding cleaning to a dirty engine. (Claim by Mobil 1 UK). Active cleaning agents + Esters.
• Mobil 1 FS X4 0W40 (BMW LL01). Active cleaning agents + Esters (37)
• Mobil 1 ESP 0W30 (BMW LL04). Active cleaning agents + Esters. Blend of PAO/GTL and Polyol Ester or Alkylated Naphthalenes.
• HPL PCMO 5W30 Euro (Exceeds BMW LL04). Boutique Blend of PAO/Ester and Alkylated Naphthalenes
• Torco SR-5R Synthetic Racing oil 5W30 (Exceeds BMW LL04). Blend of PAO, Ester and Alkylated Naphthalenes
• Redline Euro 5W30 (BMW LL04). PAO and Polyol Ester Blend. In Europe it can be bought from atomic-shop.eu or from the Hungarian parts supplier autoaz.de
• Ravenol VMP 5W30 (BMW LL04). POA/Ester Blend
• Redline HP 0W40 (BMW LL01). PAO and Polyol Ester Blend.
• Motul 300V Power 5W30 (No approval but exceeds BMW LL04). Blend of PAO/Ester
• MANNOL Legend 504/507 0W-30 and 0W40 (Exceeds BMW LL04)
• Valvoline Premium Blue restore 10W30 (Extremely effective in cleaning piston ring lands from carbonaceous deposits after only one oil drain - Virgin oxidation value greater than 120, which translates to a huge amount of esters- , but is designed only for Cummins engines) - Likely discontinued and replaced by RP -

Some of the best high PEA fuel system cleaners are:

• Redline SI-1 CFSC
• BG 44K
• Chevron Techron C+ CFSC (Made in Belgium)
• Liqui Moly Proline DI cleaner
• BerryMan FICUCLC

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

• This additive is based on a PAO/Ester (virgin Oxidation value: 110) and AN blend
• 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. The Shell HU is made of natural gas + ~20% PAO)
• At least four 5000 Kms oil changes with HPL PCMO Euro 5W30 ideally or one of the oils mentioned above
• Few hundreds of kilometers before each oil change, run one of the PEA fuel cleaners mentioned above

Valvoline VPS Top Treat Oil System Cleaner

• Powerful yet safe solvent-free engine cleaner designed to free stuck piston rings and clear tiny oil galleries
• Exists in two types, as a complete oil service and as a flush.
• Add one bottle and half to the crankcase right before an oil change and let the engine idle for 10 minutes.
• Do not use if the overall engine has excessive sludge (Oil sump thick tartar, heavily coked cylinder head) not to overwhelm the VVT oil passages.
• This cleaner is best for accelerating the softening of the piston rings deposits at the end of each OCI with one of the oils mentioned above
• Works the same way as BG EPR

Stiction Eliminator

• 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 ideally or one of the oils mentioned above
• Few hundreds of kilometers before each oil change, run one of the PEA fuel cleaners mentioned above

Triax Pro engine flush

• Triax Pro EF An excellent boutique concentrated engine cleaner based on PAO/Ester. Solvent-free. One bottle in the crankcase and idle for 15 minutes. Repeat at every oil change (at least 4)
• At least four 5000 Kms oil changes with HPL PCMO Euro 5W30 ideally or one of the oils mentioned above
• Few hundreds of kilometers before each oil change, run one of the PEA fuel cleaners mentioned above

Xenum treatment

• 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 ideally or one of the oils mentioned above
• Few hundreds of kilometers before each oil change, run one of the PEA fuel cleaners mentioned above

Auto RX Plus Engine cleaner

• Auto RX Plus is based on the natural 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

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In case of semi or 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 unless the rings are already severly worn-out). It is based on using a highly concentrated solvent-based fuel system cleaner. Products that proved to be extremely effective are:

1. AcDelco FSC and UC cleaner X66P 88861803 (GM endorsed but very Hard to get)
2. Chemtool BerryMan B12
3. BG 44K (GM endorsed)
4. Redline SI-1

BerryMan B12 Piston Soak

• Use Berryman Chemtool B12 as the cleaning substance. If You can't get a hand on B12, what you need to know is that the main carbon dissolving is made by the mixture of Toluene and Acetone which is what some Brake cleaners are generally made of.
• Otherwise, you can use a mix of 20% Acetone, 50% Toluene, 20% ATF and 10% isopropyl alcohol.
• In Europe, B12 can be found online at the Polish Carbon Clean Shop
• The Engine must be cold. Cylinder head and crankcase temperatures not beyond 40°C.
• The target Cylinder should be at BDC. Using the crank (Breaker bar with a 22mm socket) and then moving 25° back and forth. to effectively shake the B12 fluid.
• Setting the Cylinder at BDC is very important. As the N52 is tilted to the exhaust side by around 30°.
• Once your pour B12, while the Cylinder is at BDC, let it sit for few hours then turn the crank manually 8 or 10 times to allow the fluid to circulate through all around the rings.
• If you observe that the fluid has drained at a faster rate, add some spoons so that the whole piston crown gets covered again.
• Repeat turning the crank manually every 2 hours or so so that the B12 finds its way to the ring lands. Do that 4 times during the day. Add B12 if necessary. Some of it may escape to the crankcase in case of full stuck compression rings.
• Thread the spark plugs back in to avoid B12 liquid evaporation. Only 2 or 3 threads in
• Let B12 soak overnight before turning the crank manually again
• The fluid after few hours, will likely get past the rings, fill the ring grooves and then drain to the crankcase. Pour more B12 onto the cylinders and wait at least 4 hours before turning the crank manually 8 or 10 times. The purpose is to distribute the fluid evenly on the piston crown and help it flow through around pistons rings. BerryMan technical support recommends 60-90 ml per cylinder. That is for a flush flat cylinder. However for the N52, much more is needed.
• Normally in order to flood the whole N52 piston edges with the fluid, 60 ml is insufficient. At least 125 ml is required while the piston is at around BDC.
• The N52b25 for example has a bore of 82 mm and a stroke of 78.8 mm. Knowing the engine is tilted 30° to the exhaust side, we need at least 125 ml to cover the whole piston crown but not more than 350 ml as a safe maximum. This is the key point to a succesful/failed piston soak on a tilted engine. The mistake most mechanics make is pouring a safe quantity of B12 which ends up soaking only a part of the piston crown. So even with the help of rocking the piston with the crank to distribute the fluid, only the lower part of the piston gets correctly treated and not the upper intake part. This in some cases can worsen the sealing of the compression rings and thus cause cylinder compression partial loss.
  
  
• Pour more B12, wait at least 4 hours and crank again few times. Ideally use a tube similar to XADO Red Anticarbon
• 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. Otherwise the engine will be hydrolocked
• Vacuum out any left B12 from the the top of the catalytic converters eventually, through the upstream O2 sensors holes. B12 is extremely flammable. Once the engine starts, this could easily trigger a fire hazard inside the converter.
• Change the oil and eventually the filter (Make sure to prefill the filter). Use a cheap 5W30 sacrificial oil. The purpose is to change again the oil after driving the car later for 40 minutes. This way, we are sure the B12 is completely flushed from the oil system.
• Pour a tiny amount of thin oil (~ 30ml) through the spark plug wells, and turn the crank manually 5 or 6 times. Use a long thin flexible spray tube to be able to reach all edges. This is to avoid that the engine starts on dry cylinder walls and piston rings.
• B12 will strip all the protective oil film from the cylinder walls and the piston rings. It is mandatory to lube these latter before cranking the engine. Failure to do so, will result eventually in scored cylinder wall and loss of compresssion
• Vacuum out the excess oil from each cylinder. A syringe with a long tube should do. Extracted fluid must not be stored in plastic.
  
  
• It is strongly advised to plug a strong power supply to avoid heavy battery discharge
• Before even starting the Piston soak, make sure the battery is fully charged.
• At this point you may use the starter to crank the engine 8 or 10 times. This will eject any excess oil/fluid from the spark plug hole. cover the engine cover with a large microfiber, as the oil/fluid will splash all over the engine bay. B12 will instantly damage the paint clear coat and melt plastic.
• Plug the spark plugs back, re-connect ignition coils and reconnect the fuel injectors wire harness strip.
• Keep the power supply connected if needed, and attempt to start then 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.

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• TIP 1: Since the engine is angled down towards the exhaust side position (30°), jacking the car on the front right side, would help the B12 substance to be distributed more evenly around the piston crown
• TIP 2: To help on avoiding cylinder wall scoring, 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 with double vision. A scored cylinder bore or dented piston will not be fixed by a piston soak.
• 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 (successful), the driver must continue using one of the oils mentioned above, ideally Valvoline Restore & Protect ACEA C3 which has a proprietary oil additive capable of dissolving stubborn carbon from the piston ring lands.

For curiosity, BC B12 composition is as follows

• Toluene (40-50%)
• Acetone (20-25%)
• Methanol (20-25%)
• 2-Butoxyethanol (Less than 5%)
• Methyl Ethyl Ketone (MEK) (less than 5%)
• Isopropyl Alcohol (less than 5%)

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).