QUOTE(SteveG @ 2nd October 2017 21:08)

Had a similar issue - no sign of water loss but header tank would go down to about 1/3 full, no lower. Eventually, with engine running and up to temp I noticed a very fine jet of water, which I first thought was a cob web, coming out the side of the header tank to the inner wing. There was a hairline crack in the tank.
Good luck finding your leak.
Thanks for that, just been and had a really good luck but can't see anything.
I think the 146 is off to the scrap yard soon, unfortunately. Sad day, as sentimentally attached to the old girl after 18 years!
Looks like its a head gasket issue. I took the radiator out to check it over, impressed in that it took 20 minutes to remove. Well surprised everything came apart so easily. However it did show the outer legs to mount the bumper on have disappeared completely! So would need welding before MOT. Also bad idle means replacement ICV needed, although I suppose a head gasket problem may cause idle issue as well. Also sunroof rusted and leaks etc etc.
The wife has a Spider, called Slug, so I thought I'd better get that back on the road. The rear brake bias valve rusted it's pipes in the Summer, so I replaced all that and it sailed through French MOT (to my amazement). So 2 days of driving it and horrible knocking noise from the engine. So now in the process of taking the aux belt off to see where the problem is. So I came on here to find G.E.'s work through. Good grief but the work he did was fantastic! He deserves thanks for all the cars he kept on the road for so long!
Now looking at buying a cheap 147 to get us on the road. I'm currently down to my 1971 MGB GT so scraping the barrel a bit!