I have started doing oil analysis on my '02 Suburban after running Amsoil's premium full synthetic 0w-30 for 2 oil change cycles at the recommended 35,000 miles per change with filter changes at 12,500 & 25,000. At the last drain, I took a sample and sent it in to Brookstone Labs where they do a spectro analysis for $20 and give a detailed report. I also actually talked with the tech guy there. At 35k, the additive package was all used up and the oil had begun to increase its viscosity, a sign of breakdown of the oil. Of course, with the additives gone there's little protection against corrosion. So I've decided to drop back to running 25,000 mile oil change cycles, still with the filter changed in the middle. I'll do a new analysis each time the filter is changed, which'll be every 12,500 miles. I also run the same oil in our XJ8. Neither engine has given any trouble, though at 100k and 80k for the 2 cars, one wouldn't expect any. I did a cam chain & tensioner replacement job on the XJ8 recently and the inside of the engine was just about perfectly clean. You can see pics at: <http://www.willapabay.org/~rogerhol/Jaguars/> http://www.willapabay.org/~rogerhol/Jaguars/ I plan to switch a 3rd car onto this program, and in all cases we'll do oil analysis at each filter change. You learn a lot from the report and can catch a situation that portends underhood gloom before it progresses to finality. I'm not suggesting that it won't work to run a van for 200k without an oil change; synthetic oil is amazingly good stuff, and it's hard to argue with their 200,000 mile success story, if true. But it's also hard to believe that with the thickening of oil after about 25,000 miles and the total consumption of the additive package that you're doing anything but inviting an expensive disaster. Besides, why add a quart of expensive oil every 3,000 miles, along with a filter, instead of running 25,000 with a mid-term filter change and then a full drain? You spend the same or probably less and have better insurance protection. This regimen only makes sense with cars driven relatively often. Our 3 all get 20k+ per year. Our lower mileage cars synthetic we use, not. Roger '67 GT500, etc =================== It's from Roger and Jane!
