2016 Verado 300's. The other day I lowered one of my motors all the way down and right before it reached the bottom, I heard the cap pop off. I haven't touched anything there since last season.

1. I checked the fluid level with a zip tie. I wasn't getting any reading, and I stuck it down there several inches. So, I added fluid. Lowered the motor again and the cap popped off again. I just put the cap back on, and ran the motor full up and down a few times, seemed fine.

2. I checked my other motor next. When I loosened the cap I heard a little puff of air. I checked the level and again I wasn't getting a reading. I put the cap back on, ran it up and down and the cap popped off on that motor too?

3. Put the cap back on, ran it up and down a few times no issues. I ran the boat the next day and the trim seemed to work fine.

Is it possible that I have air in there causing the caps to pop off? I was worried about the cap popping off when I was in the water, but it seemed fine?