Actually cleaning out build up can be bad - you are changing an existing operating property and as a result unexpected results can occur. Having said that I think high detergent oils are the way to go.
The results obtaned are never bad in terms of the engine - only good. The most common claim is the opening of a leak. The leak was always there, the issue with the seal was always there. It is merely a fact of the removal of sludge and dirt that the leak opened up. Is this bad? No, considering that this means that your engine was dirty and now is getting cleaner. By the way, your reccomendation of a high detercent oil is nearly the same. A strong detergent/dispersant package in a fully formulated motor oil will solve and remove/suspend junk just the same as a synthetic basestock. The rates of doing this may differ, but the phenomena is the same. Diesel oils, given their design to actively suspend soot, are what one would classify as a high detergent oil. None of the standard passenger car oils would be. Further, any so-called unexpected results (such as having a leak and running low/out of oil) are the result of poor PM/recordkeeping and check-ups of one's vehicles condition. This is a fault on the driver, not the oil or the machine.
IMHO the difference between traditional and synthetics comes down to cost and service frequency. If you change your oil often there is nothing wrong with traditional oils and you will save money.
Agreed. Other than some specific situations, it is poor economy to do 3 or even 5000 mile OCIs on syn oil.
I use GTX in the 91 318 changed every 3K; Syntec since new in my MINI changed every 6K, and Syntec in my 325 every 6K. I use these intervals because they are 5 and 10K kilometers in the Great White North and thus easier to remember when to change.
You coud liklely extend those rates, motor oil has come a long way, and it generally will hold up (syn that is) in excess of 7500 miles with negligible difference in wear rates from when new.
A couple of additional benefits from synthetics are they do have longer shelf life which can be handy in low mileage vehicles, and the viscosity range is larger which also allows for less need for a change.
Shelf life is about the same for all oils. The issue is generally additives falling out of sollution in time. In that regard, conventional oils are actually better... But this is a virtue that is analyzed in years, and even in seldomly used cars, years is not a good duration for oil changes, due to the buildu of moisture. One place where syn oils are more stable is in terms of 'shear stability', or the reduction of viscosity with respect to use. Syn oils need little to no viscosity index improvers, so they stay in grade much easier. Syn oils are the best in this regard, HD diesel oils, such as the key 15w-40 oils and 5w-40 oils from the manufacturers are the next best, with standard engine oils last in the hierarchy, and still often showing issues.
The M42 get GTX every 3K or 3 months and the viscosity is 20w50 in the summer and 10w40 in winter. These are the manual's temp dependent recommendations.
Thats a fine choice - that said, motor oils have come a long way from API SG and 1991 chemistries. Though people like to make blanket statements about why the world is moving to lighter oils, please consider that everyone, BMW included has moved to lighter oils over time. It is not because there has been a significant change in tolerances and build quality in engines, changes in metalurgy, fuel economy, etc. While all of these things are good concepts, and partially true, the key thing to realize is that whether via requirement push or technology pull, the chemistries have improved so much so that a significantly lighter, more stable oil can be put into a significantly more power dense machine with all other things (build quality, toplerances, etc.) equal. This is thanks to the advancement in the shear stability, oxidative stability and enhanced performance of the additives put into fully formulated motor oils.
I hope this helps and is informative.
JMH
