today we removed the plenum to see what's happening underneath.... everything seemed fine! the HBV valve is working accurately and has no leaks what so ever, the hoses around also... the complete back of the engine is dry, so no leaking from the cooler then....
the reason we want to bypass the oil cooler is to stop letting oil in the coolant system, because it constantly get clogged somewhere and that leads to overpressure and air bubbles... today after refitting the plenum, the car had some leaked coolant underneath, but that may have been due to the work we had done... we left the car running, it heated normally, fan on, then revved it quite a bit - no leaks.... we left it to cool for a good half an hour - no leaks.... we drove it 20kms - no leaks! normal heating in cabin, normal running temperature... hasn't lost any coolant. Also all the hoses are firm and warm, as it should be.
I will not drive it until we bypass the oil cooler and flush the cooling system - after we make sure that is operating correctly and makes the right working pressure, then we check for leaks - if no such, than I will be happy.... in the spring hopefully I will get to the point of bypassing the coolant part of the cooler too and probably make a outside aftermarket cooler with a thermostat.
so puzzled today again... two days ago, before we discovered the clogged lines in the cooling system, the leak underneath the car was like you left the sink running slowly! ...