I have been testing a few of my bypass kits out on my car, Cam's PM35 and a turbo V35, all showing good results. Hopefully Cam can add his logging data to the thread later.
It consists essentially of a hose connecting the block to the coolant return line back to the radiator via the heater hose. I decided to fix the air bleeding issue at the same time, with a ball valve for easy filling and purging. I was hoping to make up some funnels to screw into the ball valve also but they aren't really required. The pushlock fittings aren't cheap and I still need to get quotes for the laser cut alloy block plates so I have no firm pricing as yet, but I need to gauge interest as I don't want to get many more than I need cut.
From my testing this kit makes filling the coolant simple, just top up the radiator, start the car, then fill through the ball valve. One closed it seals the system but allows simple air bleeding as required.
It allows more coolant to circulate through the radiator, keeping temps much more stable. I have done a few track days recently and although the temps rose it was much less than I would usually see, and the stock radiator I am using was coping well. (shame the gearbox didn't stay as cool.) On the dyno the coolant temps were more stable and when pushed it would rise, then drop back to normal straight away making the tuner more confident with multiple high power runs. I feel a larger radiator would still help keep the track temps under more control.
Here are a few instal pics, the hose will require heat shielding from the exhaust as you can see.