Packing Vent Temperature of Reciprocating Compressor

We are operating the reciprocating compressors of ARIEL JGT/4. They have trip security on the packing vent temperature.

Suction Temperature: 35 deg C

Discharge Temperature: 100 deg C

Alert on packing vent temperature: 121 deg C

Trip on packing vent temperature: 135 deg C

Last week we were facing the problem of high packing vent temerature which reached upto 132 deg C. We replaced the packing and initially the temperature rose to 125 deg C but gradually decreased to 65 deg C. I have following queries;

1- Why the packing vent temperature is higher than discharge temperature when the packing is leaking ? As after passing through packing rings the temperature must drop due to throttling effect, also ideally speaking it may not increase beyond the value of discharge temperature

2- The metal (cast iron) back up ring (radial cut) has zero clearance with the piston rod, what is the rule of thumb about the metal back up ring clearance with piston? As i believe that initial temperature rise is because of rubbing between the ring and piston rod which subsided with passage of time.