illy said:
25k per change thats crazy! the oil does break down? that seems a little extreme to me
Of course it is extreme... But, I've been doing that with vehicles since 1977 and most of mine run in excess of 250K before I sell them, and they are still not using oil at that point.
I do change the filter at mid-point of the year and add a quart of oil (or whatever is needed to top off the system). No filter will last that long, but TRUE Group IV oils certainly can and do last that long.
Early on, I tested with Blackstone, but my tests always came back clear, so I decided to forego the testing for the most part, just sticking to my regular schedule of annual changes. Many years I run less than 25K miles, so that is the outer limits, and when I do run that many miles, it is because I am doing a LOT of highway driving, which is generally lighter load than city stop and go, with constant accelleration and frequent stops.
For the record, oil really never does "break down." Rather, it gets clogged with contamination from combustion process, over-heating, etc. With proper (by-pass) filtration, synthetic oil could last 100K miles and many have done just that with frequent oil testing to verify oil condition. Used motor oil is often re-cycled and sold as semi-synthetic (and tests well!). One popular brand that does this is Wal Mart's house brand oil, Supertech.
Also, the high costs of pure Group IV synthetics that many complain about is offset by less frequent changes.
Here are some rough numbers to consider:
Pennzoil -- 6 chg. @ 3000 mi -- 5 qts 5W-30 @ $3.00 per qt -- $15.00 -- $90.00 per year or per 18K miles.
Fram Filter -- 6 change @ 3000 miles @ $5.00 -- $30.00 per year or per 18K miles.
Amsoil -- 1 chg @ 18,000 mi -- 6 qts. 5W-30 @$8.00 per qt -- $48.00 per year or per 18K miles.
Wix Filter -- 2 change @ 9,000 miles @10.00 -- $20.00 per year or per 18K miles.
Totals: Pennzoil and Fram -- $120.00 Amsoil with extended interval change -- $68.00.
And, I will suggest that Amsoil is better oil at 18K than the Pennzoil is at 0K miles... I have a TON of anecdotal experience to back up my personal views of the difference between oil and filter choices mentioned above, most having something to do with engines throwing rod bearings before 100K miles and some having to do with what an engine looks like when the intake is removed during the rebuild process (and confirmed by my long-term machinest, who tells me he can tell his customers which oil they ran simply by looking at the internals of an engine).