A biased reply, based on 25 years of using and selling AMSOIL

AMSOIL for the top line, Mobil 1 my next choice.

The others have very good products, but (except for Redline, far as I know) they all use Group III base stocks, which can approach but not reach the capabilities of the Group IV (PAO) stocks. There is also a significant difference in additive packages.

Many years ago, in the dark ages, I ran some oil analysis on my 1985 245 turbo wagon (before I put a bypass filter on it). The oil samples showed the oil suitable for continued use after 11,500 miles (1 year and 3 times the recommended drain). I dumped it then, mostly because it was starting to look bad. Now that is the backup car, and I have a bypass filter on it. I usually change it every other year.

Without oil analysis, I'd use AMSOIL for twice the recommended drain (or 1 year) in a turbo, for 25-35,000 miles (1 year) in non-turbo.

After the initial ATF change (complete), I change what it is in the pan evry 50,000. Differential fluid stays in for life (check level from time to time) unless the car gets parked under water.

I would not try to extend the factory recommended drain interval with any synthetics other than AMSOIL unless I used oil analysis. However, any of the name brand synthetics should be easily capable of going the reommended drain.

I won't bad mouth Mobil1 motor oil (although I would never try the real longer change intervals with Mobil1). Mobil1 is second best to Amsoil in readily available oils.

I will challenge their inferiority in gear oils. The small difference in price for solid performing gear oils and ATF such as Amsoil or Redline is easily justified in low wear, longer lube life, etc.
--
http://www.fidalgo.net/~brook4/oilslubesfilters.html

I use Mobil 1, with amsoil sdf 42 filter. I change it twice a year (filter and oil). If I didn't have a small leak, I'd use Amsoil oil, but at at least 1.50 more a quart, its not really worth it.

Roguls
New York, USA

Best value is Mobil 1 or Valvoline. Better quality in Amsoil and Redline, but much more expensive (unless you live near Pablo S or Dick in Falls Church).

I use Mobil 1 with genuine Volvo filters on my 965. I change it every 10K miles. I had the oil analyzed at 5K and then at 10K to know how often I should change it and at 10K the oil was fine. I just don't go over that b/c it's a nice round number to remember.

Lance