How many bars on your temperature gauge do you guys have when the temperature is almost or past 90 C (or any temp) without AC? With AC?

 

With the stock cooling system you should always see 3 bars, period. If you ever see more you should pull over immediately and let the car idle with the heater on full heat/full blast.

 

I think that the heat range of a single bar is pretty broad. I have the Mugen Thermostat / Thermoswitch / Radiator Cap, and I get up to 3 bars within 1 minute. I've taken temp measurements side by side with another stock S2000 at extended idle, and found that there was at least 20 degrees F difference, but both showed 3 bars.

 

I added a redline water weeter on my cooling system. It works really good on my previous turbo car.

 

It's been shown (see for example http://hondas2000accessories.com/serv03.htm) that the 3rd bar first comes on when the coolant temp reaches about 120 deg F, and the 4th bar lights at about 220 F. So, there's a 100 degree range captured in that 3rd bar. Presumably Honda intended this to represent the full-scale normal/safe operating range for the car, so that you could check the temp Goldilocks-style (2 bars = too cold, 4 bars = too hot, 3 bars = just right!).

BTW, did you mean 90 F (e.g. ambient air temp)?

 

twhhoos is right.

I have a digital temperature gauge and it's usually at about 120 degress F when the stock gauge hits 3 bars. In normal conditions, the water temp ranges from about 160 to 185. When it gets higher, the fans cool it down to about 175. My digital gauge also records max temp during a run, and I've never seen that over about 210.