Nice to hear that others have experienced long warm up time. Here in MN, my NSX seemed to take forever to warm up @ 25-30 degree temps. I clocked it anywhere from 12-15 minutes. I was actually concerned that the thermostat had failed, but I guess it hasn't.
This does bring up an interesting question. I plan to have all the coolant hoses in my 91 NSX replaced once water returns to a liquid phase in MN and was curious if the thermostat should be replaced at that time as well?
I have been experiencing long warm-up times, beginning very recently. Based on my research on prime, I really don't think long warm-up times should be the norm. In my car under normal warm-up, the heater used to begin providing warmth after about 2-3 minutes, with full heat after driving 5 minutes, this after a cold start with no idling, ie start and go. Recently, warm-up has taken more like 12-15 minutes. Granted, it is cold and snowy here now, but I still think this is too long.
Yesterday, I added coolant (50/50 mix) to the overflow bottle under the rear glass. On the way to work, it took the same long period to warm up. But on the way home from work, it started warming at the usual point. If the coolant is
very low, it will cause overheating, but if it is only low, then I think it causes the car to warm up more slowly. If you are experiencing slow warm-up, my recommendation would be to first add coolant to try and achieve the proper level. Only after ascertaining that there is sufficient coolant should you consider the thermostat as the possible culprit.
If after you are satisfied that the coolant level is correct, then I think thermostat failure becomes likely. Reportedly the NSX has a rubber gasket that frequently swells and breaks, causing the thermostat to become blocked open, causing slow warm-up. Aftermarket thermostats eliminate the rubber gasket and work just fine.
The good news is that the thermostat is very inexpensive. Pep Boys sells a Stant (very reputable brand) 180 degree (oem temp) thermostat for the NSX for less than $17 (I called them yesterday to see if they had any in stock; they did). Even the oem Honda thermostat isn't terribly expensive. If you are an intrepid do-it-yourselfer, you could probably replace the thermostat for less than $20 (thermostat and a little coolant). I think you could get thermostat replacement done at the dealer for less than $250.
If I were having the coolant hoses replaced, I absolutely would have them to go ahead and do the thermostat.
