[Perfectlap]

You're correct and that prompted me to go through my notes. I had the coolant tank replaced two years ago. and in looking that up it turns out I've had this sudden drop/bubble before, the first time I did a coolant flush after the car was 10 years old, or a year before the old coolant tank split. Seems like each time the cap is taken off the coolant tank, I end up with a drop in coolant some time later. First time was the flush and recently with the waterpump. I still have the car's original 2000 cap....

I'm not sure if this is a factor related to the cap issue, but both drops in coolant seemed to occurr when ambient air was hot (over 90F) and I was driving the car around for at least an hour.