that's possible, I have a gauge..
There was the beginning of coolant boiling in the plastic reservoir.
I think the coolant in the overflow tank was just on the verge of boiling, but I shut off the engine (both times) before that could really get going, so not sure about this.
Assuming a properly functioning cap and a properly sealed (aka no detectable leaks) system, Removing the cap in and of itself would have caused the evidence of boiling you saw....IOW you created your own "problem."Yes, both the radiator and reservoir caps were properly installed during my two brief op-checks. Both times, immediately after shutdown, I removed the reservoir cap and peeked in and thought I saw a few bubbles starting to form. Not conclusive, but I didn't want to risk any more damage.
Radiator condition is a question mark.
I am not stating that removing the rad cap caused the overheating, I am stating that removing the rad cap would reduce the boiling point of your coolant instantly. If the coolant was already boiling with the cap on, taking it off would only exacerbate the problem.The story on my previous X was, the orange Dex-Cool mixed with the standard green antifreeze already in the system, creating a thick gray sludge that ruined the entire cooling system, including the heater core, and ultimately caused me to sell the car as a test mule to a 'programmable EFI' developer.
And Dan: I did not remove the reservoir cap while the engine was running! I only removed it right after shutting down. That did NOT cause the overheating. Also, I had made a radiator drain plug repair and wanted to check the integrity of that under pressure before adding a full 50% of antifreeze, so the coolant at that time was mostly distilled water - I'd guess probably 70-80% water. Thus the boiling point would have been a bit lower than your numbers for 50-50. Regardless, the temperature was climbing out of control.
I am not stating that removing the rad cap caused the overheating, I am stating that removing the rad cap would reduce the boiling point of your coolant instantly.
Evidently the 850 cooling system is a conventional rad system with an overflow reservoir....not an expansion tank like an X1/9.Dave said he removed the overflow reservoir cap, not the radiator cap. Removing the reservoir cap wouldn't do anything, regardless of the engine running or not.