Quote:
Originally Posted by DBS404
Dont get me wrong mate, i admire your enthusiasm and diligance in this subject, not to mention the interest it brings to the forum, but few people have the time, inclination or ability to carry out these tests and these are the people that the manufacturers must protect.
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You have a good point- for most people in most cars it makes sense to follow the manufacturer recommendations carefully, whatever they may be rather than turn you car into an experiment. As a mechanic, you would put yourself in a dangerous position of being personally liable for failures if you maintained peoples cars differently than officially specified.
However:
1) I think the D24/D24T may be an exception, since not using Group IV synthetic seems to result in stuck rings, and rapid engine wear (unlike most diesel engines such as Mercedes which seem to experience only about twice the metallic wear rate on non-synthetic). Since our engines require nearly 2 gallons of oil, extended drain intervals with synthetic are really the only economical option for us. The fact that our engine manufacturer (VW) actually specifies extended drain intervals on synthetic for the TDI (a newer evolution of the same engine family) also lends credibility to this approach.
2) In some cases people have bought into marketing hype (from companies selling oil) that 3,000 mile changes will improve engine longevity, so they're actually using shorter intervals than their manufacturer recommends. They probably should follow the factory interval instead, since there is some evidence that needlessly shortening the interval could accelerate, rather than reduce wear.