norbs is on the money, also note that most toyotas run at approx 82 degrees, your fan is effectivly trying to cool the engine cooler than its proper operating temp, this is probably why the fan will not turn off.
the optimum setup would be to only need the thermo fan when u are sitting in traffic, with an efficient cooling system, normal driving should keep the temp floating around 82deg. so ON at ~90 off at ~85 is not a bad setup
i kint blemember my exact fan on/of temp settings but on regular 25degree day stuck in traffic my fans only need to run for 30seconds at a time.