Is a 4WD vehicle necessary?

For standard national park loops, no. A standard sedan or SUV is fine. Only rent 4WD if you plan on exploring unpaved backcountry 'BLM' roads.

How do I handle the heat?

Start your day at sunrise. By 1:00 PM, you should be back in your air-conditioned car or a shaded area. Never hike into a canyon during mid-day.

Road Tripping the American Southwest: A Practical Strategy

To see the major sights of the American Southwest, allocate at least 10 days to cover the loop from Las Vegas through Zion, Bryce Canyon, Page, and the Grand Canyon. Rent a high-clearance vehicle, book your park lodging 6-9 months in advance, and stick to a strict sunrise-to-sunset schedule to avoid the worst of the crowds.

Secure your vehicle and permits. Rent a standard SUV for better visibility and clearance on park roads. If you plan to visit more than three National Parks, buy the $80 'America the Beautiful' annual pass at the first park entrance to save money.
Map your route by drive time. Do not drive more than 4 hours per day. The landscape is vast and monotonous on interstates; stick to 'Scenic Byways' like Utah Highway 12, which turns travel into the main event rather than a chore.
Sync with park peak hours. Arrive at park gates before 7:00 AM. Parking lots at Zion and the Grand Canyon South Rim fill up by 9:00 AM. Plan your heavy hiking for the early morning and use mid-day for driving to your next stop or visiting indoor museums.
Manage your water and fuel. Carry two gallons of water per person per day in your car. In remote areas of Utah and Arizona, fill your gas tank whenever you drop below half, as stations can be 100 miles apart.

Is a 4WD vehicle necessary?: For standard national park loops, no. A standard sedan or SUV is fine. Only rent 4WD if you plan on exploring unpaved backcountry 'BLM' roads.
How do I handle the heat?: Start your day at sunrise. By 1:00 PM, you should be back in your air-conditioned car or a shaded area. Never hike into a canyon during mid-day.