mk1 golfs suffer from the water jacket on the oil cooler rusting through putting oil in the water or vice versa if you are getting pressure build up in the water system then more than likely headgasket can you get it to a garage for a sniff test
Thats because they grip more if you had 50psi the tyres would more than likely spin rather than grip Same as if you are doing 1/4 mile sprints you lower the pressure to create bigger footprint of tyre on the track
ask your self why you got rid of the rado and golf b4 then ask yourself what possesed you to buy a Beemer. you should be able to answer your own question lol