It won't hurt, but I wouldn't rely on changing it 5-7K. Yes I know oil can go that long if not longer, but if I'm going to be anal enough to dish out the dough for syn then I might as well be anal to do it every 3000. Truthfully though, I do mine about 3-5K.

 

Why do they recommend to switch to synthetic at 12-15k miles and not when the car is brand new? Or within the first 1000 miles?

 

Well as the story goes, more friction is present with dino oil versus synthetic which allows for the normal break-in process. Use synthetic too early in the engines life and expect a prolonged break-in.
My feeling is that total engine performance only occurs with a total break-in so why delay this process with a synthetic in a new engine?
I realise that a few new autos come with synthetic installed but the S2000 is not one of them. My advise- Break the car in with dino and then if you want to switch ,go with a synthetic.

 

a few posters mentioned early... once you switch to synthetic, stay synthetic. Mixing dino and synthetic isnt the best idea.

As far as waiting too long goes, 25k is not too long.

The only worries that are had when switching from dino to synthetic is in higher mileage motors, lets say 90k+.. depending on how you drive of course.
The myth is, is that when switching to synthetic from dino at higher mileage causes leaks from one or more seals. The extra cleaning additives in synthetic help clean as well as lubricating.. as i call "shampoo". If you've used dino oil for 100k, dirt may have built up around the seals and actually help seals not leak. When you switch over to the synthetic oil w/ cleaning additives (shampoo).. it helps clean the motor and clean the seals...
but what if the dirt was really helping the seals not leak? Then switching over to synthetic just caused you a big headache, as you would start seeing oil leaks.

So thats the myth. I personally have not seen any oil leaks from my motor (1997 Honda Prelude), and i switched to synthetic at 130k, b/c i was starting to drive more... its a personal choice to switch on a daily driver IMO.

 

I'd take that with a grain of salt, there are a lot of cars that come with synth from the factory.