Folks -

Interesting situation, and I didn't see the same symptoms in the archives:

Car warms up and drives fine, temp to middle of the range no problem, probably 85-90 degrees C. In traffic (this is winter, mind you, ambient temp somewhere around 45 degrees F), car will heat up to a solid 110 degrees, until I turn the heater on full blast, at which time the temp drops IMMEDIATELY back to the temp as noted above (85-90). If instead I rev the engine, it drops some, but slower and not as far. Thoughts?

-Reed
1990 300CE
1984 300D-T
1970 BMW 2800