Get your Coolant from the dealer (Honda Type2 Coolant I gallon OL999-9011 x2). Techinically you are supposed to able to use any Ethylene Glycol based Coolant that is free of both Silicates and Borates. Never Dex-Cool (orange).

Long story short, just buy Genuine Honda Type2 from your dealer. I think I got 2 gallon jugs for $16.00 even. I wouldn't bother trying to find a substitute. I did some reading about Coolants (several years ago now) and basically they are formulated differently for different cooling systems. Some contain additives that are actually supposed to plug microscopic holes in the system over time. I'm not talking about the "fix-a-flat" stuff for radiator, just coolant. Other's are supposedly additive free. If the wrong coolant is put into the cooling system or mixed into a system it can cause serious damage.
Just use Honda Type2 coolant, it is the right stuff for the S2000's cooling system. Don't mix it with your Type1 coolant. Flush the system first.
I have no way of knowing if it is true, but I have been told that Honda's coolant is a high quality product regardless.

 

hey thanx for all the info. Why switch to type 2 if my car already has the type 1. Wouldnt it make more sense to just keep using type 1.

 

I think it is discontinued. That dosen't mean you won't be able to find some really old stock somewhere. One reason would be once it is Blue you will be to visually identify what type of coolant by color, as there is no Blue Type1.
I also just noticed that there is more detailed info on Coolant change in the Owners manual then in the Service manual. I actually just went out and filled my resivoir to MAX line with the system cold.
I also noticed this in the Owners Manual (MY03):

Always use Honda All Season Antifreeze/Coolant Type2. This coolant is pre-mixed with 50 percent water. It does not require any additional mixing.
If it is not available, you may use another major-brand non-silicate coolant as a TEMPORARY replacement. Make sure it is a high-quality coolant recommended for aluminum engines. However, continued use of any non-Honda coolant can result in corrosion, causing the cooling system to malfunction or fail. Have the cooling system flushed and refilled with Honda antifreeze/coolant as soon as possible.

It sounds a little more urgent then the normal "We recommend only Genuine Honda" marketing spiel.

 

Yup, that's how it works. The coolant level needs to be at least between the Min/Max.
The cooling system will self bleed through the reservoir. Even though you bleed the air from the system when changing coolant, some air is still left behind.

 

Thanks for the clarification Slows2k.

 

you can use any coolant in the S2000 as long as the label on it says silicate-free. if its a different color then what you have in there now, do a drain, flush, and fill.