I shall now describe a specific situation with my car. At one point, the liquid in the radiator is boiling and the engine began to overheat. All topped up - went there for a couple of hours. After inspection found the problem - the junction of the radiator and expansion tank. Decided to remove and glue sealant - but did not last long. Removed the ring from the radiator cap (to relieve excess pressure) and put on a heavy-duty sealant - the result was better. Now flooded liquid was enough for a few days, then had to top up. And I pour water became normal. In this mode it was possible to ride, but was a fun little romp with checking the level and topping up with (this time for water to evaporate through the cover without rings). Besides, winter is coming, and constantly pour antifreeze is expensive. Something had to be done. And just needed to find the reason why e36 radiator was created excess pressure, which led to the problem of a leak at the junction. The same pressure and does not allow to properly seal the junction of the tank with the radiator.
Now about the problem. The problem of excess pressure in the cooling system of the engine is primarily a valve cap from the expansion tank. With it you can remove one or both of the sealing rings, and correct replace with smaller valve pressure. Costs about 10$ to 15$. And only by removing the excess pressure in the system can be satelilite the junction of the tank with the radiator. Or try something different-to change the gasket for example. If the pressure in the system will remain, it will not work to fix the leak for a long time.
Let us mention here another problem of the cooling system, which can be together with the excess pressure. If you have cars jumping the temperature of the engine - say constantly above or below normal, then you need to check the thermostat. It is on the bottom larger pipe between engine and radiator.
Replaced easy. Only need to pre-drain the engine cooling system. Then unscrewed, replaced, spun, poured and all.