From the sounds of it, I'm not sure that you had your coolant expansion tank plumbed correctly.
The bottom connection is an outlet from the expansion tank back into the cooling system, and the top connection is for bleed/steam lines. The connection on the neck is an overflow to atmosphere (or an overflow bottle), and should only be open when the pressure cap opens.
The bottom connection should be plumbed to somewhere lower like just before your waterpump inlet, not the top (steam line) of your radiator, otherwise air may not be able to escape from your radiator if the top of the rad is higher that the bottom of the tank.
The top connection(s) are bleed lines, which should have small diameter pipes from the high points in your system, such as the top of the radiator, top of the engine, and perhaps the highest point around the heater matrix. These allow any air in the system to escape to the top of the expansion tank. When the system heats up and the air expands, it pushes the coolant in the tank down into the system. The expansion tank should be mounted as high as possible, so that the airspace inside the tank is higher than the rest of the cooling system.
There should only be one pressure cap and it should be on the expansion tank. If you have a cap on the radiator, it should be a plain sealing cap (and the bleed line from the rad needs to be open all the time, ie. not the pipe on the rad neck which will be closed off by a sealed cap).
Coolant filling is then done via the expansion tank only, and should be filled to about half full. The bleed lines in the system mean that you just pour your coolant in and as the level rises, any air gets squeezed up to the top of the system, then exits via the bleed lines into the expansion tank. No messing about trying to burp the system or anything like that.
Anyway, sorry if I'm teaching you to suck eggs. Car looks great by the way. I'm sure it's terrifyingly fast.
PS. if I were you I'd take a trip to a scrapyard and look for a larger, clear plastic expansion tank that you can squeeze in somewhere. It's much easier to see what's going on with a clear one, and your one there looks a bit small for what is presumably a large cooling system.
The bottom connection is an outlet from the expansion tank back into the cooling system, and the top connection is for bleed/steam lines. The connection on the neck is an overflow to atmosphere (or an overflow bottle), and should only be open when the pressure cap opens.
The bottom connection should be plumbed to somewhere lower like just before your waterpump inlet, not the top (steam line) of your radiator, otherwise air may not be able to escape from your radiator if the top of the rad is higher that the bottom of the tank.
The top connection(s) are bleed lines, which should have small diameter pipes from the high points in your system, such as the top of the radiator, top of the engine, and perhaps the highest point around the heater matrix. These allow any air in the system to escape to the top of the expansion tank. When the system heats up and the air expands, it pushes the coolant in the tank down into the system. The expansion tank should be mounted as high as possible, so that the airspace inside the tank is higher than the rest of the cooling system.
There should only be one pressure cap and it should be on the expansion tank. If you have a cap on the radiator, it should be a plain sealing cap (and the bleed line from the rad needs to be open all the time, ie. not the pipe on the rad neck which will be closed off by a sealed cap).
Coolant filling is then done via the expansion tank only, and should be filled to about half full. The bleed lines in the system mean that you just pour your coolant in and as the level rises, any air gets squeezed up to the top of the system, then exits via the bleed lines into the expansion tank. No messing about trying to burp the system or anything like that.
Anyway, sorry if I'm teaching you to suck eggs. Car looks great by the way. I'm sure it's terrifyingly fast.
PS. if I were you I'd take a trip to a scrapyard and look for a larger, clear plastic expansion tank that you can squeeze in somewhere. It's much easier to see what's going on with a clear one, and your one there looks a bit small for what is presumably a large cooling system.