After having read all this good stuff, here and elsewhere on the BB, I'm still wondering if the volume of coolant moved by the pump might be a bit too small for B20s on warm days. In my case, idling at a traffic light moves the needle to where it's almost into the white portion way on the right hand side of the scale (544). Yet, when I give the accelerator a good jab the needle immediately goes back to vertical normal. I find it difficult to believe that making the fan spin faster for such a short time, let's say 3 seconds, would have such an immediate effect on the temperature of the block. I could believe that, at low revs, there is stagnant coolant sitting in the aft end of the head where the temperature sensor lives, which would not be inconsistent with so many gauges reading high while IF thermometer readings at other locations on the block show up normal.