Loop heat pipes (LHP) combine the classical heat pipe operation principle with a loop configuration, i.e. evaporator and condenser are located at separate places as dictated by thermal and configurational reasons and are connected lines for fluid and vapor transport. Experimental investigations of such LHP revealed certain temperature oscillations under certain conditions. This paper presents the results of analyses of such temperature fluctuations and offers possible explanations for initiation and termination of such behavior. Two types of temperature fluctuations have also been confirmed experimentally by testing different kinds of LHP.