I used a pusher to bring an E-Class (approx 1550t) into an aerobraking maneuver, and it will start to overheat at 63000m (asteroid and craft were traveling approx 3200m/s), and will explode under 45000m leaving the attached craft to continue onwards without exploding. I have screen shots of a decent into Upper Kerbin atmosphere without dipping below 50000m but shows the temperature gauges rising and nearly maxing out.