I run Mobil full synthetic, in my modified (bored, cam, high compression, etc..) SBC S-10, NAPA (WIX) filter. I'm in no hurry to switch over my '99 Silverado, though I probably will eventually.
I've also run full synthetics in other cars (VW, BMW) with no problems, even after other oils had been used.
Keep in mind the type of driving you're doing. If it's hard miles you're putting on the engine and you're changing oil every 2000-2500 miles or so, you are still doing your engine good as long as it's a good brand oil. Changing to a synthetic will ultimately give your engine longer life but there's the added cost of a synthetic to consider as well. Products like Red Line were desigend for more extreme conditions. Thus their molecular struction will show superior to that of conventional oils, synth. blends and even Mobil1.
Changing brands of oil was thought to actualy help sludge build up since different brands contained differnt additives and would break each other down but still provide protection to engine vitals. With the advancements in oil technologies I'm not sure this applies any longer. I personally don't consider any truth to changing oils and oil usage unless going from a good brand to some generic discount brand.
