Assessed the new toy, will give it a decent tidy up in the weekend and hopefully get it installed:

https://autotrader.co.nz/showroom/subaru/subaru-announces-trio-of-sti-tuned-special-editions-for-tokyo-auto-salon   Like shuffling deck chairs as the Titanic goes down...   Why don't they pull finger and build a real STI.   🤣  

Indeed, I know its not the most accurate spot, but purity and all that. I'm not too concerned about absolute precision (otherwise Subaru would instruct differently ie cylinder 3 gallery plug), more just gauging that I'm in line with other systems considering all this stuff is almost 30 years old   I still wonder how in the heck it could ever read 120-130+ in that location though...

ooh it's a haze of those days when I cared about that stuff hah, yeah 90 sounds about right?   A tapped Drain plug is also the coolest spot? (heat rises) and ya getting max airflow / cooling in the area too if you've not got a undertray too

OP isn't a regular here anymore and I'm not ECU savy : but the 1st question is But why?   is your car Auto?