Have you you checked the coolant system for pressure when cold? If the upper rad hose is solid when squeezed, and the car builds pressure rapidly after a cold start, before it warms up, you may have issues with the cylinder head. If the cooling system is pressurising itself through a crack in the cylinder head, the cooling system can get very irratic, temps can vary, seemingly for no reason, say climbing rapidly at idle, etc. The system is also unable to draw from the overflow tank hidden in the wheel well/front fender area (124). I sincerly hope I am wrong, and that it is something simple unrelated to a -14 cyl head issue, I'll keep my fingers crossed.