Water lines oem why did they do that???
 

thinking about my recently rebuild 1.8 block I am left with a few questions:

Waterlines:From the water pump the coolent is going 3 ways.
1 through engine to the heater core
2 through engine to the oil cooler , the trottle body and to the thermostat
3 directly to the thermostat.(->radiator-> waterpump)

My 1st question: how can there be any flow in the oil cooler (youll have the same pressure @ both sides (at the cilinder head)

My 2nd question: the small hose between the waterpump and the thermostat wtf does it do??? (youll hook the turbo onto this hose)

3th question: is the coolent coming from the heater core cooled enough or are w just inserting hot water into the engine again?

Maybe you can route it back after the thermostat so all hot coolent goes through the radiator.

regarding #3, that is the purpose of a partial bypass. It takes the hot water and puts it into the radiator to be cooled instead of back into the engine.

On your question 1, I believe that it is to keep coolant moving at the thermostat and thus have it react quicker when closed.

I did a coolant rerouted on my 97. The coolant now leaves the heater and goes back to the rad directly. It takes longer for the heater to get hot, but the water temp never creeps up like it used to.