oil temp goes up when turkey breast is dropped - why?

WHY DOES MY OIL TEMPERATURE GO UP FROM 350 TO 400 OR 425 WHEN I LOWER A BONE IN TURKEY BREAST AND THEN IT WILL REMAIN THERE FOR ABOUT 20 MINUTES WITHOUT THE BURNER ON - TURKEY COOKS FINE BUT THIS PUZZLES ME - ANY THOUGHTS (HAVE DONE THIS TWICE NOW WITH SAME RESULTS)