Having it towed is over reacting a bit. If damage was done, it's done, and if you can drive it now and the temp is normal, then don't risk some tow truck screwing up your car.
You didn't mention if it was a hot day and/or if you had the AC running, which makes a big difference.
There are four major possible causes:
~ 1 One or both radiator fans not working. This is the simplest to test. Let the car idle while you monitor both fans and the temp gauge. Turning on the AC will also start them, but that does not prove they will turn on thermostatically.
~ 2 Coolant was low for whatever reason, which could be for any number of reasons including a leaky hose, water tank, radiator core/tank, water pump, blown head gasket, cracked water jacket, etc., etc. The really bad ones are also least likely.
~ 3 Stuck or weak thermostat. This is my bet if you have not recently replaced the coolant or otherwise messed with the cooling system in some way. It is not uncommon for an old thermostat to start opening at exactly at the correct temperature, but then never open all the way. That of course restricts flow and can cause your problem. When you replace it out (which you should anyway after a bad overheat) suspend it and a new one side by side in a pot of water on the stove. As the water temp rises, watch them both closely and see if the old one ever opens all the way.
~ 4 There is an air bubble in the coolant system. This is my bet if you have recently replaced the coolant. The NSX cooling system is tough to bleed properly because the radiator is in front and the engine in back. What the book does not tell you is that when bleeding the system from any given point, you should jack the nearest corner of the car up a few inches to encourage the air bubbles to come toward the bleeder. If this is the real problem, then you could have started to drive and instantly seen the temp fall back towards normal. Not because of increased air flow, but because the air bubble was pushed through the system and your temp gauge sees the real water temp. I have seen this more than once.
There are other possibilities, but I would start with these.
Good luck.
[This message has been edited by sjs (edited 29 March 2002).]