re: High Mileage trucks

I tend to default to Synthetic oil and I personally think Synthetic is more efficient for higher mileage vehicles.

I typically use 10W-30 and it just depends on whether high mileage is available. In a high mileage vehicle, i'd keep it 10W or lower and 30 or lower. You want quick oil flow at cold start up since internal components can become more worn out at higher miles. And the higher viscosity you go (30 and above), the heavier the oil, meaning the slower it will flow. Again, same premise for higher mileage vehicles in that you want better oil flow.

Synthetic oil tends to seal and lubricate gaskets better than regular oil, IMO. Better may be a lose term but I believe Synthetic extends life of the motor by decreasing leaks and offering better oil flow. Just my .02.