[99LeCouch]

Running synthetic is good for the environment since it can go 2-3 times as long on a change. For the transmission, it runs cooler. That extends the life of the transmission before rebuilding. And, it requires fewer fluid changes since it doesn't degrade as fast.

Running the thinnest oil your car can safely run is another way to get statistically better fuel economy. A 0w-XX oil helps with cold-start lubrication by getting pumped around faster than a 5w-xx or 10w-xx oil.

I have 5k miles on the synthetic 5w-30 (well, it's really 5w-20 since it's a very thin 30 weight) on my Buick. It won't be changed until the springtime, when it will have accumulated 10-12k miles.