Coolant level, defender 90 1989/200tdi conversion, Metal expansion tank.

Can anyone tell me what the coolant level should be in the metal expansion tank - The Haynes manual refers to the seam half way - but makes no mention of what type of expansion tank - I understand there are different ones, the later being plastic. The engine looks to be losing coolant , droping from half way level, and I'm wondering if we are over filling the tank. I searched here, but can't find any info.

About half is right for most coolant tanks. When I fitted a 200 into my 1990 truck I fitted the plastic tank for a Defender. Don't know if it matters but has greater capacity.

Thanks for the reply. Seems we prob have bigger problems with coolant being ejected and the heater filling with gas!