Synthetic Oil Change Intervals ???

Advice and opinions please....
I'm currently doing oil changes (w/filter) at 3500 miles using conventional oil.
Many posts indicate using synthetic oil offers protection far superior
to conventional oils.
What I would like to do is move the oil change / filter interval from 3500 to 7500 making it compatible with the 15K 30K 60K mileage service intervals.
Is using Synthetic and a good filter at 7500 a good move....or
should I stick to 3500 w/ conventional oil.
What's your experience... I've heard that Shell's Rotella is a good oil, so is Mobil 1. Still undecided on the oil filter to use.
Car is a 1990 Oldsmobile Silhouette APV with 77,000 miles. Normal use, no stop and go.
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Here I have a mix of City/Highway driving (50/50 or thereabouts). Have been using a 10,000km (6,200 mile) interval for oil & filter for many years w/o problems. Mobil 1 5w-30 & AC-Delco filters. I would think 7,500 miles is not much of a stretch. IMHO the major factor is the amount of sulphur in the gasoline. You Americans have a major advantage over us Canucks for the moment there. Much cleaner gas south of the border. Averages something like 150ppm US vs 600ppm Canadian.
Regards, Al.
On Thu, 10 Jul 2003 11:11:32 -0400, Peter <> wrote:

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I use Amsoil here, and NO I'm not a dealer so I'm not trying to sell you anything. I use the Series 2000, oil filter change at 6 months or 12.5k miles and oil/filter change at 35k or 1 year, if I'm not mistaken. Been working great for me for a few years now. And go ahead and bash or try to say something else is better, I don't really care, Amsoil works for me :)
On Thu, 10 Jul 2003 11:11:32 -0400, Peter <> wrote:

-GV
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