by jp928 » Thu Jan 17, 2008 10:22 am
I have been at a lecture by a Ryco filter man and the filter change topic came up. He pointed out that all filters are a compromise between getting out the particles that matter, and time to clogging. If you start taking out say 10micron particles from start, by the time you have all these and larger out, the fabric will be starting to clog early. Most normal car filters aim at 20micron starting up, and as the 20micron pores get closed, the smaller particles will get caught as well. In short, changing filter TOO early before its started to take out the smaller particles can defeat the purpose somewhat.
The best type, if you can get them, are those that combine a normal bypass section with a full flow section - the bypass takes 80% of flow, and ensures that no part goes without oil; the full flow takes the other 20%, but its going to clog before the bypass section. Some 4x4s have such filters available AFAIK.
Also a guy in a Porsche list decided to systematically test their 15k mile (24k km) oil change interval by doing a base test on an oil (Mobil Delvac 5w40) new, and then follow up with Used oil Analysis every 3-5k kms. In a hard driven 1990 928 (5l V8) over a year doing 15k kms, every test came back as "Suitable for continued use" from the same test lab. One test showed a blip in Silicon, and when he checked , the air cleaner element had come off its seat and was letting dust past.
Conclusion was that in modern engines with modern oils, changing at less than recommended intervals in normal usage is a waste of money.
jp