I have an audi 97 a4 6 sylander and i had to change the metal pipe wich transfer water from reservor to termostat housing do i need to bleed the system after fix and soo wher is the bleeding valve thanks fred

Yes you need to bleed the system. There is a hole in the coolant hose going into the heater core. Back of engine at the firewall . Loosen the clamp and slide the hose part way off the pipe. Add coolant to the system expansion tank until it flows out of the hole in the coolant hose . Slide hose back onto pipe and tighten the clamp. Close cap on expansion tank ,turn on heater controls , Start engine and run at 2000 RPM for about 3 min. Continue running engine at idle until the lower hose on the radiator becomes hot. Check coolant level in the expansion tank and add if necessary when system is cool. DO NOT open expansion tank cap while system is HOT.

You dont have to bleed the water it automatically takes out the air when it runs and the thermostat valve opens check the level again after a run of 5 miles or when the temp is in the middle

remember not to check when the engine is hot