before you start unhooking the coolant lines to disconnect the cooler , I've read you can drain like a quart of coolant out so you don't have to bother with any coolant mess , but when you are done and you put the coolant back in , has anyone had any check engine lights come on from too much air in the coolant lines ? or should you put the car in maintance mode and run it like you did a coolant change?
That was probably me. Yeah, I'm not sure how much you need to drain, but I guessed 2 liters (or quarts) would be plenty, and that worked out. Keep in mind a small amount of coolant is trapped at the back corner of the cooler: just be careful not to tip it when lifting off. When everything was reassembled, I poured the coolant into the reservoir (it was quite low once drained, but not completely empty) and the level ended up a little high, maybe 1/2" higher than at the outset, at the most. As I was pouring it back in I burped a few of the big coolant hoses within reach. I also, left the air-bleed bolt open. That's on a hose, just above the cooler, on 2010~2011 model years. In 2012 Toyota deleted the air-bleed bolt, not sure why. Still, I would think of you just disconnected a hose, right at the former bleed bolt location, and quickly reinstalled when coolant started coming out (as you refill), it would accomplish the same thing. With a day or two driving the car, the coolant level settled back to normal, with no further intervention (say running the car in maintenance mode), and I didn't get any codes.
