Good Morning all; Can you guys help me with a viscosity decision? I've searched the forums but haven't been able to get a complete answer on which conventional Pennzoil to use in my two cars: 00 Chevy Impala 3.4 V6 pushrod 55K miles 98 Volvo S70 non turbo Inline 5cyl 67K miles. Both run very well and burn no oil. The Chevy manual says 5W-30 year round, but 10W-30 OK if temp >0F. Volvo Manual says 10W-30 OK for -4F to 104F, but 5W-30 OK if temp <86F. To make things more confusing, I called the local Volvo dealer and they say they use 5W-30 all the time - maybe because they sell & service Toyotas too? I'd like to stick with one viscosity year round, and change every 5K/6 months. Should I go with 5W-30 in the Chevy and 10W-30 in the Volvo? Seems backward to have the lighter oil in the pushrod and the thicker oil in the overhead cam engine. Or should I go 5W-30 in both for the faster flow at startup/fuel mileage, or 10W-30 in both for the better oil stability? Does it even matter which one I use? Thanks for your time!