There is a procedure see:
Ok; it covered before somewhere but here goes:
1. Park car on slope with nose upwards (aids air bleeding),
2. Put heater on highest setting.
3. Remove thermostat and thermostat housing top.
4. Fill to top of thermostat housing via thermostat housing.
5. Replace thermostat (make sure its a dual acting one with
6. Replace thermostat housing.
7. Fill rest of system using a funnel to full from the small
bleeder hose that is on top of the thermostat housing and runs
to the coolant overflow bottle; hold hose in air above highest
point of engine or radiator while doing this).
8. Replace bleeder hose and top up over flow bottle.
9. Screw cap on overflow tank loosely one turn.
10. Start engine (heater still on max setting) run for 10
minutes at 2000 rpm or go for a 10 km drive.
11. Let cool top up and tighten cap.
12. Have a beer and toast the Ford engineers who designed such
an air lock prone system.
If you're changing coolant brands flush with distilled water
before doing this (i.e. fill with distilled water and go for a
20 km drive, let cool then change coolant).
If you don't follow the correct procedure (which originally was
on a sticker on that coolant bottle) those air bleed hoses may
eventually purge the system but don't count on it; and in the
meantime risk overheating or doing the pump in. The plastic
supply tank has a min and max mark on the side but fill it to
about and inch below the cap; just so the tips of your fingers
get damp when you stick them in.
A hole in the T stat might help accelerate the system self bleeding but....I've never needed to do that yet.
Also make sure you have the original type dual acting thermostat
fitted. See http://www.vtr.org/maintain/stag-cooling.html