Quote Originally Posted by Valda View Post
And у них жар is nice and short. Can I use it instead of температура and лихорадка ?
Жар and температура are mainly interchangeable but former is normally used for a moderate increase of body temperature while latter - for a strong one.

Лихорадка is mainly used as a part of specific disease name (hay fever, gold fever). There is a verb "лихорадить", but if usually refers to the general feeling of distress, unhealthy excitation and tremor, rather than high body temperature ("Меня лихорадит").