Originally Posted by Groucho
BTW how often should tranny & diff fluid get changed? My commute (mostly high speed from sea level, over a 4500' mountain, then down into slow traffic) is probably fairly tough on these...
This is a tough one and I've seen it debated many different ways. AMSOIL recently reformulated its best gear lube. In reading about this reformulation, it seems the industry is coming to believe the most severe gear lube application is high performance cars like our vice long haul trucking. Seems diffs in street cars, particularly ones like ours, see pretty extreme conditions: high heat intake from the exhaust running right by them, low airflow (hence no cooling), small fluid volume, high RPM, etc. AMSOIL rates this new gear lube, which is designed for this severe application, for 50,000 miles in severe duty, which I feel is reaasonable for our cars. Personally I fail a little conservative on this and change my diff fluids at 30k (my Vette I change it every 8 track days or so).
AMSOIL Severe Gear Extreme Pressure Synthetic 75w140
Tranny fluid is a similar thought. AMSOIL rates its ATF for triple the manufacturers rating which again is slightly outside my own comfort margin. I change my tranny fluid also at 30k. I've reached 30k on my F350, but not my wife's Trailblazer yet. Again, my Vette gets tranny fluid changes every 8 track days or so.
Given how many miles you put on your car, you might consider this oil from AMSOIL which meets the manufacturers specs, is warrantied by AMSOIL, and rated for 35k or one year. I'd suggest you start slowly and change the oil at 12,500 miles which is what AMSOIL rates their filters for. That's double what you are getting now, but still fairly conservative given what the oil is rated for. Once you are comfortable, particularly if you do some used oil analysis, you will probably be able to comfortably extend that further.
AMSOIL Series 2000 0w30