Persistent Coolant Venting Under Load: Good Cap, 0 Misfires, 216°F Peak (Graph Attached)

Hey everyone,

I’m dealing with a persistent coolant venting issue on my 2010 Gen 3, and it's driving me crazy. I'm attaching a Torque Pro graph of my coolant temps from a recent long highway trip for context.
The Symptoms: After long, sustained highway trips (ambient temps are very hot right now, around 95°F-100°F / 35°C-38°C), my engine coolant reservoir level drops, and I get pink crust spraying around the cap threads and around the side of the coolant reservoir.

BEFORE THE TRIP COOLANT LEVEL:


AFTER THE TRIP COOLANT LEVEL AND VENTED PINK CRUST AROUND BOTTLE


Work & Diagnostics Completed (Radiator to EHRS): To get ahead of the usual suggestions, here is everything my mechanic and I have already addressed, verified by live Torque Pro data and physical inspections:

• Radiator & Loop: System serviced and checked for standard external leaks. To be absolutely certain about flow, I replaced the electric water pump rotor. I verified its flawless operation multiple times via a professional scanner, and even physically disassembled/inspected it twice. It is pushing coolant perfectly.
• Reservoir & Cap: Scrubbed the bottle clean to track new residue. Swapped the engine cap with a known-good OEM 108 kPa (16 PSI) cap. Verified the side overflow nozzle is completely open and unobstructed. It still vented coolant on my last long drive.
• Engine / Head Gasket: I am logging all 4 cylinders in Torque Pro, and I have exactly 0 misfires across hours of driving. Engine holds perfect compression and runs beautifully smooth, even under sustained 93% load on steep highway inclines.
• EGR System: The complete EGR unit was previously removed and deep-cleaned by my mechanic. My live data confirms it is moving freely, stepping perfectly from 0 up to 71 steps under load.
• EHRS (Exhaust Heat Recovery): System serviced. The internal flap is definitely unstuck and functioning. My logs show EHRS temps successfully peaking around 239°F (115°C) on the highway, proving it is routing the extreme exhaust heat properly.

The Data (See Attached Graph): As you can see in the log, my engine coolant temp (7E2) fluctuates normally but peaks at about 214°F to 216°F (101°C - 102°C) during heavy uphill highway stretches.

Graph1: Different temperatures against other PIDs

Graph2: Cylinders misfire graph against other PIDs


If the system is sealed with a good 16 PSI cap, the head gasket shows absolutely zero signs of failure, and 216°F shouldn't be hot enough to boil a fully pressurized system, why is it still pushing steam/coolant past the cap?

I would love to hear your thoughts on what I should investigate next based on this data.
Thanks!
Ali