Just recently, my ls/vtec swap (b18a1 block,GSR head w/ ctr pistons) has been acting up. Basically, whenever I get on it now (anything up 6-7k) about 1 minute after I got on it, my heat suddenly goes cold; the temperature gauge goes a bit past the halfway point towards hot, and sits like this for about 20 seconds.

Then it just immediately cools off, like the temperature gauge just drops back to normal.

sometimes it will do its cycle one more time and then it is fine again. I'm not sure what's going on, so any help would be appreciated.

 

Try checking your coolant level and changing your thermostat if it hasn't already been done. Its cheap and a good idea for maintenence anyway. Also take a good look at your rad to see if there obvious damage like missing fins. It sounds like your car overheats when you get on it. I had damaged rad awhile ago and it caused the same thing, cool during slower driving (low rpm), hot when driving faster (high rpm). Good luck