HeatFX was disabled a few builds ago as it caused gfx issues on a few cars ("distortion bubbles" is my best description). Have not seen it been enabled again.
The feature is still there, working like a charm. Just drive the EVE at Spa 66 and you'll notice. S397 simply don't add it anymore to new cars sadly. (BTW, it is a terrific sight to start from the back and see the heat around the engine along the straights. Same goes for the long gone birds at Mills Metro Park. All this stuff added so much to the immersion. Maybe it is just me but it made rf2 uncomparable.) Anyway, I would love to have it back and blown up into the hole scenery,....calculated.