As the title states, I'm just wondering if I should do it like you'd normally bleed the s5's cooling system and turn the heater on.
Or if anyone had a better idea?

 

Does that series five RADIATOR have a pressure cap?

IF it does...........loosen THAT cap. Then fill at the series four neck at the water pump (I assume you have a pressure cap there and remove it to fill). IF the cap is loose on the radiator water will start to flow out around THAT cap. So as water flows out there, put THAT cap back on good while still filling at the waterpump.........til you overfill at the water pump and then stop and put that cap back on and your through.

In other words the cap on the radiator is where you bleed air off if your a series four with the original filler at the water pump and have a radiator cap on the series five radiator. THAT cap is the bleed screw.

 

http://www.handsontools.com/Lisle-24...it_p_5079.html

Turn the heater on high, and fill with this guy. Let the car idle like that for about 5 minutes and presto.... no more air bubbles.