Dumping coolant again

[mozzie26]

Last week I did a track day at Lakeside on my GSXR750K5 and the guy next to me had the same model K4. His bike did the 8 laps in the 15 min sessions ok until he came back into the pits then after about 3 mins sitting there shut down the coolant in the expansion tank would start to boil and spew out the over flow hose. Did the same thing the next two sessions too. When the bike came into the pits the display read 97 degC when switched off but the temp would rise after shut down and spew coolant back out over flow. He was a bit worried because he had only just had the engine rebuilt.
We pulled the fairing off to top the coolant back up. He said he had replaced the radiator a few month ago but to me it looked like it was second hand. The cap locking tabs looked a bit damaged and suspect as well. I recon he had a blocked radiator core that was not cooling enough.
I run my track bike with the rad fan removed and have no problems.