Check to make sure the heat sink is well-seated. High temps usually mean poor contact or poor-grade or insufficient thermal grease. Try reseating the heat sink. This is usually the culprit in my experiences. Monitoring the temp is quite demanding on the CPU so it raises the temp quite a bit (from my experiences anyway). 87C is very high (much above about 60C is likely troublesome). I don't know about the warranty part though.