Bleed air from cooling system after fluid change

[prydey]

Hi guys.

I have a 2006 LS focus 2L. I drained the coolant via the drain plug on the bottom of the left radiator tank. Drained about 5L out, give or take. The book says its 6.5L system, but obviously it doesn't all drain out. Filled it back up but it only took about 4L until the header tank was full. I then ran the car with the cap off, and with the heater on full, until well after the car had warmed up (10-20min). I expected the level to drop as the air dissipated out. It hasn't changed.

I took the car for a drive. It warmed up as per normal, but then the temp gauge dropped back to about 1/4. Drove around for around 10min. with the heater on. Everything seemed fine. Got home, popped the bonnet and the level is still the same. Also there was no pressure in the system. I was able to remove the cap as soon as I popped the bonnet. Hoses felt hot to touch, but no pressure.

From inside the cabin, I'm pretty sure I could hear the sound of water running when I turned the car on. This has me believing there is still air in the system, most probably in the heater core or somewhere in the heating system (although the heater works well).

Could the cap be cactus? The car has always seemed to take quite a while to warm up. Prior to doing the flush, the level was good. If the cap was no good, wouldn't it force water out the overflow?

Any ideas to sort this out? I'm assuming if it is just air pockets it will just sort itself out naturally over time. Just have to keep an eye on the level.