Yes normal.... temp difference in garage creates pressure that yes will push fluid out wherever it can. It's common for someone to park in a heated garage with a full tank of gas and then get evap problems because fuel was pushed up and into the vapor canister, destroying it.

A good safe practice is to never, absolutely ever leave gasoline unattended. Period. I mean in a gas can, but not while you have the fuel system torn apart. Also I hope you had a proper fire extinguisher that is rated for gasoline withing arms reach. Fires happen quick which can lead to an explosion... blowing your garage apart and possibly killing someone.

Think about it.

Al

 

Yes, fire extinguisher is present. I just found it odd, because I changed the filter about two years ago and only remember a few ounces dribbling out.

 

Yes, fire extinguisher is present.

But no operator present - just saying. Don't take it personally, but I've seen a service station explode when they were draining a gas tank in the winter with the doors closed and the gas fired water heater lit. Blew every window out of the shop.

 

Differential pressures can do this, but the general reason would be you created a siphon.

Since the fuel level is higher than the now open fuel filter, it will drain until the fuel level is at or below the fuel filter opening. If the siphon is strong enough, it will drain your tank, since the fuel inlet is at the lowest point in the tank.