Hi Paul. It's so far so good with the Honda radiator running without a header tank.
The length of hose I have running back to the bulkhead with the in-line filler in it gives plenty of extra coolant capacity and the water level remains constant after running it up to operating temperature. I haven't tested it on a long drive yet as I'm still at the moon rover stage and don't have private land to hoon around on like Phil J does, but it sat at idle on a blazing hot day for over an hour without overheating, so it should be fine at speed with air being force fed through it.
The only possible issue is that I haven't managed to get the heater working yet. I've put a bleed valve into the return hose but I don't seem to have any flow into the matrix - I can take the cap off the bleed valve completely with the engine running and no water comes out. I've primed it by filling the heater hoses with coolant but it just sits there doing nothing with the cap off. I don't think that's anything to do with the radiator though, it's more likely a blockage in the original heater feed hoses.
If anyone's an expert on the Vitesse heater system btw I'd appreciate any ideas on how to get mine working...
I'd say that the Civic radiator is a good bet for fitting to any Sammio as it's compact and does the job. I've gone for the standard one intended for engines up to the 125bhp 1.5 vti at forty quid brand new. It
does look very small and thin compared to the old Triumph one it replaced, so if you want something that looks a bit more substantial then the alloy racing version of the same is twice as thick and great value at about £75 delivered.
I'm sure there are other suitable radiators available - I believe Trevor B used a Golf rad in No.48, but I couldn't find a new one from any other car at anywhere near the price I paid for the Civic one.
Good luck finding a suitable rad, it's all part of the challenge.
