We've had a lot of discussions about that clutch.

One of the members was in the identical situation and replaced the clutch. He found the same symptoms with the new clutch and concluded it was defective. So he returned the clutch and received a second new clutch that performed the same way as the first clutch.

Apparently, the clutch won't fully couple until the temperature of the bi-metal spring is in the area of 105°C. This is a very high temperature and would require the coolant temperature to be higher than this value because some heat is lost in the radiator.

It seems that the calibration of that clutch is much higher than what we would consider "normal". Understand that replacing it may not provide you with any better results.