Tires: Tires, inflation pressure, radial tires

Question
are eight ply tires subject to dangerous overheating at turnpike speeds. Years ago I experienced several blowouts with 8 ply tires.

Answer
First, the term is "ply rating" and its use is being phased out because people think that it refers to the actual number of plies in a tire - but it doesn't fit well with radial tires.  So I will use the term "Load Range" and translate your "8 ply" to "Load Range D".

Provided a tire is properly sized, properly inflated and properly cared for, Load Range D are no more prone to blowouts than Load Range C or E.

However, It has been discovered that many vehicles, especially SUV's and pickups, would benefit from larger load capacity tires, so most of the newer vehicles went that direction.  For some this meant an increase in tire size, but in many cases this was simply a change from Load Range D to Load Range E (and a corresponding increase in inflation pressure)

Hope this helps.