Originally Posted by SouthArk370Z

Stick with your 30 weight. The engine was designed for 30; 40 will be too thick for optimal operation. 40 probably won't do enough damage to worry about (more stress on the pump, &c), but why use the wrong stuff when the right stuff is readily available? If you were making long hauls in the desert, there might be an advantage to using 40; for everybody else, stick to the factory recommendations.