I replaced my mono valve a few weeks ago, due to lack of consistent heat. The job was pretty easy. One comment I had read previously was that you would get coolant leaking out of the opening when removing the unit, so the advice was to take some out prior to the job... which of course I did not do! So, in doing the job I really didn't notice that I had a pretty good amount of fluid leak out. When I started the car up I hit the panic button... white smoke everywhere, coolant smell, and when I looked on the ground under the car there was a huge puddle of coolant ! Yikes!!
Well I shut the car down and spent a good amount of time cleaning the garage floor and also the inside of the engine area where I also noted a good amount of fluid had found its way down! I examined everything looking for loose or cracked hoses, and went over everything I had touched, but found nothing. I started it back up and spent another 10 minutes searching for leaks to no avail. As I did this, the smoke went away, the coolant smell went away and everything looked good. My bad... I should have drained some fluid beforehand. All was and is well. And I have heat!!