How's that pressure test of your engine worked out?
I'm not saying it's related but it can be - I once a had a lancia delta hf integrale, I blew the head gasket on that engine 3 times.
Every single time before it happened I got coolant or/and oilproblems and then problems staring the engine when hot before the engine failed totally.
Usually game over in the morning when cold actually.....
After a few years I considered myself a master in changing the engine head gasket in that cramped integrale engine compartments
That 2 liter lancia engine was a marble, the most entertaining and sporty enginge I've ever driven, as long at is was working mind you. I wish I could have a flawless working lancia 2L 16v turbocharged engine in my A3 - that would have been great
Well, back to your engine - A human with a cold doesn't like to run, A sick engine will not accecpt to be pushed hard.....
I say get your engine sorted before chipping it or you
might be sorry....