Temp Drop - Yeast problem

My latest 10 gallon (in 2 carboys) batch was fermenting nicely in a large cooler with water to act as a temp buffer. It was brewed on Wednesday and I pitched 1000ml of good starter into each carboy. The fermentation took of nicely but the temp began to ramp up from 68 yesterday as it was about 90 degrees. There was a nice 2 inch krausen and I just cracked a window in the room to keep it from ramping up any higher, it had already climbed from 68 to 70.

Well, got up this morning and the damn things had cooled to 66 and the head had disappeared almost completely. I brought it up to 70 again and gently shook the carboys. There is some fermentation still going on but I'm pretty sure I shocked the yeast.

Should I just take gravity readings and chill or should I prepare a second starter ASAP and repitch?

It dropped 4 degrees overnight? That should be quite alright. Think about yeast surviving outside. If they freaked out every time it dropped 4 degrees, they would lose at life.

If it's still going, you'll be fine. 4 degrees isn't that big of a deal. I wouldn't recommend letting it happen again, but it shouldn't be a problem.

And I usually ferment all my ales around 66, so that temp shouldn't hurt the yeast at all.