Puking Coolant

[Rev Run D]

My m20 was overheating spitting coolant out of the overflow tank, so I pulled the head, assuming and thinking that it would be the head gasket. Took it to the machine shop to get it checked out, and it was cracked where the rocker shaft goes through. The machinist told me that the head wasn't worth rebuilding, and so I went and bought a brand new M20 with valves installed. Installed new rockers, new rocker shafts, and a new cam, and bolted the head back onto the block.

Started it up, and the problem is still there. Second verse, same as the first, a little bit louder and a little bit worse. What might it be? What next step should I do to troubleshoot?

[zaq123]

blocked radiator..., stuck thermostat, bad radiator cap...

[Rev Run D]

Radiator has minimal run time. thermostat and radiator cap was replaced with head. Pukes coolant out of the reservoir with cap off.

[zaq123]

Radiator has minimal run time. thermostat and radiator cap was replaced with head. Pukes coolant out of the reservoir with cap off.

it's normal for it to do that with therad cap off, the entire system (including the tank) is under pressure up to 1.4 bar (rad cap rating, 140 cap). Pretty common issue on these when the coolant level sensor cap gets deformed or its seal goes bad, the car will constantly be losing coolant. Not your issue but it's the same effect you are seeing with the cap off.
You probably think of the tank as an overflow tank (typical car design) where it is being fed after the radiator cap. On E30, the tank is the part off the pressurised system.

[tomstin]

Raise the front of the car, turn the heat on full, run the engine and bleed the air out using the bleeder screw. Use a thermal gun to verify the radiator is working completely. How is the cooling fan and clutch? Search "newspaper test" or replace the fan clutch. Will it cool going down the highway and only overheat in traffic or idle (classic fan clutch)?

[zaq123]

Raise the front of the car, turn the heat on full, run the engine and bleed the air out using the bleeder screw. Use a thermal gun to verify the radiator is working completely. How is the cooling fan and clutch? Search "newspaper test" or replace the fan clutch. Will it cool going down the highway and only overheat in traffic or idle (classic fan clutch)?

I guess I missed the part where he said "overheating". If the coolant not just puking but puking with air , definitely air in the system. Bleed screw on the thermostat housing is high enough to bleed the system well. HF has a power coolant bleeder for $80 which uses compressed air to really get all the air out if your bleed screw seized up