I have my 1.8 Blacktop plumbed in as per Raceline's spec, i.e. no expansion tank, pump to bottom rad, with a heater take off, other heater take off on the raceline rail, stat housing out to to top rad, rad is V8 MGB so plenty big enough.

The car runs fine and doesn't overheat, but if it has been hot enough for the cooling fans to kick in, when I switch off, it spurts about a cupfull of coolant out of the overflow?

I'm thinking I need to upgrade to an expansion tank? anyone had a similar problem?

I had the same using a Rover header tank with I think a 7lb sq/in cap. Fit a Ford one which are 14lb sq/in and all OK. Suspect newer engines run higher pressure.

I have the same setup. I assume you have the modified cross-flow TS housing on the rail with a pressure cap fitted? If so run a thin diameter tube from the overflow on the TS housing to a drinks bottle with just enough coolant in it to cover the end of the pipe.

Additionally if you've not already done it, either hollow out the TS or drill a 3mm to 5mm hole in the ring opposite the ball bearing. Mines hollowed out, which gives enough restriction during the warm-up phase but allows good flow when hot.

Dan