If the power washer calls for a straight 30, the Rotella would be a good choice. As said above, the 10W30 version (either the original or the T-5 semi-syn) would also be good choices. If the pressure washer is used only in warm weather (hey lets's go out at -30 and pressure wash something???!!!) then the thinner oil might be more advantageous. You are fine either way. All the Rotella products are quality.