90 degrees seems about right to me. It's only when it gets over 100 that you have to worry.
However, there is a very simple and effective way to make your car 'cooler' (and no, it doesn't involve 18s).
There is a conversion known as a 'top-hose' conversion (usually done on Integrales etc, but it works on all cars.)
The temperature sensor that measures the water temperature is normally located at the bottom of the radiator. The conversion involves removing that sensor and relocating it in the hose that runs at the top of the radiator.
A simple 'T' bracket is required to mount the sensor in the top hose.
Are you all following so far? Good.
You have to use another sensor to blank off the now vacant hole at the bottom of the radiator. This sensor performs no function other than to blank off the lower hole.
Right, now as we now, heat rises, so the top of the radiator will get hotter before the bottom of the radiator and therefore, a top mounted temperature sensor will register 90 degrees before a bottom mounted sensor will, having the effect of making the fan cut in earlier. (the fan cuts in at 90 degrees normally).
Having this conversion results in the fan cutting in before 90 degrees, as the sensor is tricked into thinking that the engine is hotter than it actually is.
Clever ain't it.
The car runs noticeably cooler (even if it is on 18s !) especially stuck in traffic. You can feel all the warm air being blown away from the engine if your window is down.
Over heating is a major cause for gaskets to perish and leads to engine failure.
The 'T' bracket costs £12. The conversion takes 10 minutes.