I have also found that things do not work well.....fluctuating temp. etc......if there is air in the system.
Having to add a gallon of water would indicate that a lot of coolant has been lost.......someplace.
It IS normal for the water level to rise as the engine warms up.....and when the cap is on, the coolant will go into the overflow bottle.
Then when the engine / radiator coolant cools down....the coolant is sucked back into the system.....from the overflow bottle.
Now, if you have a leak........coolant will go out through the leak.....on the warm cycle.....and then.....air can be drawn in on the cool cycle.....which will then cause all the problems of a air pocket in the system.
The water will be flowing through the "bypass" tube, through the heater hose that goes out on the driver's side.....through the heater core.....then back into the engine on the passenger side.
A blocked thermostat will not interrupt the flow of coolant through the engine, or heater.
When the thermostat opens, the coolant will flow OUT to the radiator through the TOP radiator hose.......into the top, driver's side of the radiator....
There is a plastic "tank" on each side of the radiator......and it is hollow from top to bottom.
The water will flow through the alluminum radiator tubes....to the plastic tank on the passenger side.
Then the coolest water will flow down to the bottom radiator hose....and back into the engine.
Take note that if you have air conditioning, the fins that you see on the front of the radiator are the air conditioner condensor coils.....not the radiator fins.
So.....that said.....the bottom radiator hose will be the last thing to get warm.
I am guessing that you have a leak.....which is causing you to loose coolant.....and then air is being drawn into the system......which is going to cause things to not work well......especially if air is at the water pump....as it will not move air enough to push water.....
I would say to look for steam in the exhaust to see if it is a head gasket or lower intake manifold gasket.....but at 20 degrees outside.....there will be a good amount of steam and water dripping out of a good engine.....and the mind can play tricks (been there also)....now if you have green coolant.....you could see if you have green water dripping out the tail pipe.....
Again, 1 gallon is a LOT......so you should be able to locate the leak.....
FIRST place I would look.....would be one of the heater hoses......or that pesky little elbow (if the '95 has it).......it is a "U" shapped elbow....only about 6" long......a metal tube comes out of the water pump.....pointing toward the firewall.....and then there is a small hose that connects to it.....that turns back toward the radiator.....and connects to the water bypass tube.
I have a picture of the water bypass tube posted in my pictures.....
But...again......they used a different intake manifold on the 95 than on any of the other years......but really give those heater / bypass hoses a good look.......as it is much cheaper and easier than some of the other options.