fitting new coolant header tank

[elsid]

I have just fitted a new header tank to my 1985 T25 fitted with a DG engine. I siphoned the coolant out of the old tank before removing it and fitting the new one. On refilling the tank it only took half the coolant that came out, I squeezed all pipes in the engine bay and had a few air bubbles come out. I opened the vent on the radiator and it was free of any air, I opened the vent on the large hose at the front of the engine bay and nothing seemed to be happening. I ran the engine up to temperature, the radiator got hot all over but the top long hose along the front of the engine bay was only warm. Despite running it up and cooling it down I can't get anymore coolant into it, in fact even when cold if I tried to remove the cap coolant comes out. I am concerned there is an air lock in the system which could cause the engine to overheat. Everything seems perfect when running it, temperature gauge stays normal but it idles faster than before. I find it difficult to understand a cooling system where the top of the radiator is 10" higher than the header tank! I find it even odder when both the Haynes and the Brooklands manuals say you should jack the front of the van up 15" making it even higher! The Brickyard method says there is no need to jack up the van. I have read through loads of posts on the forum and Wiki and tried just about everything without success. Has anyone encountered this problem? Would it be safe to take the van out for a run or is there a risk I could boil the engine?
Sid

[lloydy]

I'd take it out for a drive, get it nice and hot. The air in there will soon shift. I've found after draining and filling mine I've had to top up the expansion tank a couple times over the next few days. You'll never get all the air out first go

[elsid]

I took the van out for a 10 mile run today. Everything seemed OK, the heater was hot and the temperature gauge stayed in the middle. The header tank was still full to the top and the expansion tank was still at the same level. The top pipe running across the front of the engine bay was still only warm though, perhaps that is normal! I still can't understand why it took 2.1/2 litres less coolant to fill it up than came out when I drained the header tank. I am going to Cornwall in the van on Sunday towing a trailer so I hope it is OK!
Sid.