In the first part of this paper we recall the difference between nonionic and ionic amphiphiles with respect to the effect of thermal energy on their distribution between water and oil and the consequences that result therefrom for the preparation of microemulsions if temperature, the composition of the oil, and that of the brine are prescribed. In the second part we demonstrate how to monitor the position of the three-phase interval of ionic microemulsions on the temperature scale by means of an "lipophilicity scan", that is, by using a sufficiently lipophilic double-tailed ionic amphiphile and varying its effective lipophilicity by adding either a less lipophilic single-tailed or a more lipophilic double-tailed ionic co-surfactant.