It can go both ways. The air can just not let the fluid decrease pressure. So when the air gets compressed and then de-pressurizes, the fluid has no where to go because of the air pocket.

Welcome to the most divided question there is.

Does it ruin your engine? Does it not? You’ll hear both sides.

Here’s my take. My ass is cold. I prefer it to be warm in the Car. Therefore, that shit is getting remote started until it’s warm. Consequences be damned.