This may be adumb question but my Cobra has a normal radiator cap on the header tank with open ended overflow pipe. Now every time I switch off, heatsink causes it to pump out some radiator fluid onto the garage floor or road which means that I have to refill the header tank every 3-5 trips with about 2 litres of fluid.

Can I simply convert the system to a closed one by replacing the header tank cap with a closed system cap and putting in (and piping up) an expansion bottle with radiator cap or is there more to it than that?

Could try the simpler system used on some Japanese cars including 1990s Hondas simply lead the overflow to expansion bottle open to atmospheric pressure.

If I am right the MX5 has an expansion bottle which allows coolant to vent when hot and suck back as it cools. Seems to work ok.Might be an easy mod to make.

Yeah on most jap car the overflow catch bottle is mounted on a neat little bracket, an old idea invented during WW2 for the 8th Army here are a couple of photos of SAS Jeeps (one real one wannabe) showing what they called a surge tank.

I would like to mess with these guys !
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