have you checked the accelerator pedal position sensor on the shock tower? has the cable to it snapped off - similarly check under the dashboard for the cable connection to the pedal. (mine did that once, the cable was popped off) - car had no error code and a dead gas pedal.

then also check for the check engine light and whatever corresponding error code it has recorded.


the reason its reaching beyond 80C is because its not moving, (no airflow on radiator and the fan will lazily spin when its 95C) - the sludgy mud on the cap is a bit strange, if it were mayo like - then its normal for it when its only been abt 10 minutes after cold start.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)