That's not so different - It's acting just like mine on my T-1.
Maybe because it's easier for the coolers to keep you under 210F by opening the valve at 180F, than it is by waiting til you're at 200F and trying to quickly bring it back down?
There is probably some old French formulae from my ancient Thermo-Dynamics class that explains all that, but I most assuredly was asleep during that lecture. I just know that oil heats and cools faster than water (which is good for most of us).