Burping a 1992 radiator & cooling system

There are two types of cooling systems. Closed which has a pressurized overflow bottle and open which has an unpressurized bottle. I have a 1992 XJ 4.0 auto trans with the open system. I've found info about burping the closed systems and a little about the open ones but I'd like a definitive answer addressed solely to open systems.

After a recent engine swap I simply filled the radiator all the way up via the filler neck and filled the bottle to the full mark. My thermostat has a small hole in it which I drilled and positioned at 12 o'clock. The engine has been thru several heat/cool cycles.

The reason I ask is that when cold the overflow bottle is at the the full mark, but very shortly after starting it rapidly fills to nearly the top. Makes me think that there is air in the system that is expanding. I can remove the radiator cap when engine is stopped. When cold the fluid is nearly ready to flow out but when hot the horizontal part of the neck is empty.


What should I do?

Thanks!
Mike

The "full" mark is not all the way to the top because the bottle needs room for the hot pressurized coolant to escape, be stored, and then sucked back into the radiator when it cools down.

You don't really need to "bleed" the system, but if you want to get the air out it's pretty simple. Park somewhere with the nose of the jeep uphill (I use my dad's yard which has a berm next to the driveway), turn the heater on with the hottest setting (opens the heater control valve), and cycle the engine on a couple of five-minute runs. Add coolant as needed to keep air from being reintroduced.

Or you could just remove the upper radiator hose from the tstat housing and fill from there.

I like to thwap that hose periodically to help the air bleed out