Guys,
Mine just did the same thing...the SC would work then it wouldn't...it all happend on a trip coming back from Charlottesville, VA this past weekend.
I replaced the pump with the Johnson I bought last year and just never installed. Up until this trip the car NEVER had a problem even in the dead of summer with the AC on high. Anyway i put the Johnson pump in...and everything seemed to be okay going in to work and then it started again....I never checked the No. 13 fuse. It is a 10 amp fuse and it was blown. I guess the Bosh pump being old and weak, blew the fuse, but the car has just enough cooling capacity to allow the SC to kick in sometimes even if the pump is not working (this is just normal highway driving and NOT racing).

If your SC is kicking in and out and you are not racing, check the fuse and then replace the pump with a Johnson CM30 - Remember to Burp the cooling system after you replace the pump to get any air out. Your car will be screaming like never before even in the hot Atlanta Sun.

Once you start racing it, do like everyone else has recommended and seperate the system and put in a SuperCooler. You won't regret it.

Waldig has a great post and pics on Burping your cooling system after you install the pump. There is a link to it in my recent post "Loss of Power".

Good luck.

Cheers,
KrzyFast