pressure back through radiator!

[87 WE2]

Is the problem happening under boost or normal driving?

 

[Powder]

If you're really lucky you may still have air trapped in the engine, especially if your heater isn't pumping out heat. It sometimes help to purge the air by raising the front of the car then cycle the engine(heat and cool) and refilling the overflow.
If that doesn't correct your high temps then rent a coolant system pressure tester from autozone test the system. If it doesn't hold pressure and you don't have any coolant leaks than you have an internal leak. Headgasket,etc.
Good luck with it.
MH

 

[FastRegalWE2]

Mine was pressurizing the coolant too. My heads were lifting @ 10-12 PSI. I took off the steel shims and put Fel Pros on.