Well, I've finished replacing spark plugs and flushing, refilling the coolant, and replacing the thermostat and housing.

First problem: Idling too high - around 1000. Gap was set at 1.3 according the Bosch recommendation (Platinum Plus spark plugs). This isn't urgent but I need to do something, what is urgent is next:

Second problem: The god damn thermostat housing is leaking between the top and bottom housings. I replaced the thermostat, then put the black rubber o-ring on top of the thermostat so it sits between it and the top housing, then bolted on the top housing. I used a bit of vaseline on the o-ring as I have nothing else (as per another thread I read here).

Since I just put $40 worth of coolant in it, I don't want to have to drain it completely again to put in the paper gasket that came with the housing instead of the o-ring (and I read here somewhere the o-ring is better anyway). Do I need to drain it all or just take the top house off and drop the level a bit from the top house.....

Its in the driveway leaking and my only car, so quick advice would be good so I'm not there at midnight....

should've put some form of sealer in between. i used silicone sealer. just rip it off. you'll loose a little bit of coolant. and 1.3mm sounds a bit big. i though 0.9 for a Falcon

I used a gasket maker material. You need to on the housing mating faces. That O'ring does f**k as you've just noticed.

0.9 is to small for a N/A. 0.8-0.9 for a boosted falcon, 1.0-1.1 for a n/a. You'll loose f.a. coolent by takeing the top hose off. Just bend it back once you take it off a secure it back then put sealent on the thermostat housing.

There is a slot in the inside of the O-ring, which fits over the outside of the thermostat. If fitted properly the O-ring should be good.

Not much coolant leaks out when you open the thermostat top only. Best to park the car with the nose up, with the coolant cool, and with the pressure cap on to reduce any siphoning.

Thanks all for your replies but I've worked it out in the meantime. Not as stupid as I thought. Would have prefered not be finishing at 9.10pm though

Yes, not withstanding another thread saying the rubber o-ring is good, it is f*cked. I syphoned a bit out of the overflow, loosened the housing bolts a tad and let some coolant leak until it stopped, then replaced with the 'paper' gasket that came with the housing. Now its as dry as a bone.

The idle now seems to be 850 ish, but I was running the heater on full too, so I'll take it for a run when the misses calls for me to pick her up from work and see how she settles. I take it that it could be the gap effecting the idle? If it does drop to about 800, will I leave it or adjust the gap again - or see how its running first?

Thanks again, I knew I could count on Fordmods members when I got stuck.

Theres always some unknown factor when I'm doing my own servicing, just trying to get adventurous and do a few things more other than changing oil - even my grandmother could do that. In a few months I might even attempt to change the pads and replace the rotors with slotted. The workshop manual makes it look easier than I thought. Time will tell...

I keep forgetting about those stupid bloody covers on the clamp screws, it took me 30min before I twigged from once before. Christ!