where do you live and what is the climate like?
i use penzoil 10w30 in my 1600dp 365 days a year and it seems to work great. the motor runs smooth and at a good temp during vancouver city driving and long hauls (seattle, vancouver island). every time i stop for gas i check the oil level, feel it to make sure it's still \"slippery\", smell it, and then i always check it for foriegn particles when i change it out (every 2500 miles).