I will post a general guideline to what has to be serviced so that you guys get a general idea on whether it is necessary to change.
This is an alternative to BMW’s factory-recommended maintenance schedule.” It is actually BMW’s maintenance schedule, more or less. This also represents my opinion, based upon my experience and that of my readers, tech advisors, and professional BMW technicians both dealer and independent. I have prepared it because of the large number of misguidance amongst many forummers. The fact that my opinions may differ from those of others does not mean anyone is necessarily right or wrong. You will get a different answer from every person you ask about routine vehicle maintenance.
The most common reason for BMW drivability problems in contemporary cars with over 100,000 KM is that they need a tune up – spark plugs, air filter, and fuel filter.
Break-in Service for New Cars
Traditionally, BMW performed a break-in service at 2,000 KM on new cars, which included changing the engine oil and filter, manual gearbox oil or automatic transmission fluid, and differential oil. Recently, BMW stopped performing break-in services except on M cars.
I have seen that the engine and drive-line oils in new modern BMWs are literally full of metal at 2,000 KM– as has always been the case with any new car. For this reason, I recommend a 2,000-KM break-in service.
Engine
Oil and Filter Intervals
BMW recommends their Castrol 5W-30 synthetic motor oil in all BMWs except contemporary M cars, for which they recommend their Castrol 10W-60 synthetic motor oil. The factory oil change interval is controlled electronically, but is presently about every 25,000KM.. If you are running BMW’s oil, I recommend an oil and filter change interval between 13,000 and 17,000 KM. PML has since reduced this interval because many cars came in with sludge build up which required dis-assembling the engines completely and cleaning it up. This is largely owing to the fact that in our climate, oil becomes sludge fairly quickly with the default service interval that BMW Ag sets in Europe. But Europe is not Singapore in terms of weather.
Filters
Original BMW filters are recommended for price and quality, or MANN, Mahle or Bosch.
Air Filter
Stock paper element, check every 25,000 KM, tap out dirt, replace if necessary, standard interval 50,000 KM, use Original BMW filters or aftermarket filters such as Knecht, MANN, Mahle, or Bosch.
K&N oiled cotton gauze filters, clean every 25,000 to 50,000 KMs depending on condition, use only K&N approved cleaner and oil, and follow K&N cleaning procedures.
Fuel Filter
Replace every 50,000 KM, also replace if fuel pump is replaced, use original BMW filters or Bosch, Knecht, MANN, or Mahle.
Microfilter
All modern BMWs filter interior air through a replaceable fine particulate filter called a "microfilter". On the latest vehicles, the microfilter(s) are located in easy-to-reach spots under the hood and take only a minute or two to replace. Since a microfilter was an afterthought on the E36, however, it's wedged in the only place BMW could think to put it -- on the upstream side of the evaporator coil. In other words, it's under the dash in a really inconvenient location.
The microfilter is aptly named, as it is sufficiently dense to catch more than just large leaves, twigs and bugs. The before/after shot above demonstrates how well it does its job. For this reason, if left installed beyond its recommended replacement interval it can contribute to odd smells in the interior, and if left in place beyond all reason, it can clog and thereby reduce the KM, and based on my experience that's perfectly reasonable. The procedure to replace the filter is very simple in principle.
Valve Adjustment
Perform every 25,000 to 30,000 KM where applicable.
Timing Belt, Tensioner Pulley, and Front Cam Seal
Replace every 5 years or 80,000 KM on vehicles so equipped, water pump replacement also recommended as preventative attendant service, but not required.
Engine Drive Belts
Replace O.E. or O.E.M. BMW poly-ribbed serpentine belts every 60,000 KM.
Replace O.E.M. Continental or Pirelli or original BMW V-belts every 45,000 KM.
Engine Coolant Service
I recommend changing engine coolant at two-year intervals, using only factory BMW anti-freeze mixed 50-50 with distilled water (reason – BMW anti-freeze is phosphate free, phosphates cause aluminum oxidation, which blocks cylinder head coolant passages and causes head gasket failure, others may claim to be “aluminum safe” or “phosphate free” – make your choice, but I’ve used BMW anti-freeze exclusively in many cars and have never had an aluminum oxidation or head gasket problem)
Spark Plugs
There is no reason to deviate from the factory-recommended Bosch or NGK spark plug specification, changed at 50,000-to-60,000-KM intervals, depending upon the car and severity of service. Basically, any BMW produced after 1993 can easily run 60,000 KMs on a set of spark plugs.
The factory also has part numbers and applications for “Long Life-KM spark plugs.” These are good too, and are capable of high mileage of service assuming no other problems, which might cause them to foul during that time. However, in engines with spark plugs recessed into the middle of the cylinder head, oil can leak into the spark plug recesses past the valve cover gaskets. This is a hidden leak if the plugs are left in service for an extended period of time, because no one looks in there until they’re changing the plugs or chasing a problem. An oil leak in the spark plug recesses, left to fester, can cause ignition coil failure and even ECU failure. So, even if you want to leave the plugs in service, you should at least check the spark plug recesses for signs of oil leakage at least every 50,000 KM. And at the point you’re in there, you might as well replace the plugs. This is the issue with high-mileage plugs.For high compression engine like the ///M cars and Direct injection engines like the N54, change it at 20,000KM to be safe. Most of the modern BMW cars use spark plugs as knock sensors. They do not have an independent knock control system in place. So essentially, the spark plugs are also the sensors. So be careful.
Hopefully the above helps most at least interms of a general guideline on the servicing.