Thermostats normally fail in one of two ways. They can stick open and the engine takes a long time or will not get to full temperature. They can also stick closed, in which case engine temperature will normally be elevated and the engine may over heat.
RepairPal Certified shops can diagnose and repair your 1995 Toyota Celica. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.