'83 4ks TD cooling dilemma

[JIM_WALLACE@HP-Canada-om1.om.hp.com]

Greetings,
I'm still waiting for a Bentley to arrive; meanwhile, I hope someone from the 
list can help me out. I had the following experience on Saturday:

1. The car was never getting up to temperature. (Stuck open thermostat, I 
figure.)
2. Replaced thermostat with new 190 degree unit.
3. Car now begins to warm up nicely at idle.
4. Take for test drive - zoom - temp skyrockets.
5. Get home quickly, temp settles back to mid point with car idling.
6. Top up coolant; it takes about another quart.
7. Test drive again, temp skyrockets again.
8. Back in garage, doesn't need more coolant, but car is idling rougher than 
before.

Note: I took out a thermostat that has had its working section removed i.e. 
only the flange was there. I am now suspicious of the previous owner.
Then, I find the following cryptic label: (reproducing from memory only) "When 
topping up coolant, open the thermo timer switch on the outlet adapter on 
cylinder head. Close again when fully drained." That's right, you're both 
topping up and draining simultaneously by the looks of this message.

So,
a) where is this switch and what's it look like? There are lots of sensors etc. 
on the head.
b) do I have an air lock someplace?
c) do I need a water pump?
d) is it something else? Like maybe the coolant will only leak through that 
previously undetected crack in the head once it gets good and hot?

At one point I thought the thermostat might be in backwards but it only fits 
one way.
Any input is appreciated; the car is out of service until this is either 
resolved or I go back to the thermostat flange only, but then I can't defrost 
the windshield.

Thanks in advance,
Jim Wallace