Overflow bottle

[tyasman]

When I bought my '68 Elan, the overflow bottle has been replaced with a coke tin into which the pipe from the radiator sits. It is not sealed. I notice the manual states the bottle should have a sealed top. Is this necessary? The car runs a bit hot and I'm wondering if this could be the cause as it means that the radiator is effectively not pressurised.
I'd be grateful for comments

[alan71]

I noticed that too, ?over flow tube must be an air tight fit on both bottle and radiator?. I can see why it needs to be airtight on the radiator to suck coolant back as the system cools. If it was airtight at the bottle it would pressurise the bottle when there was any overflow, is this necessary? I think the important thing is that the tube is always below the level of fluid.

Alan.

[types26/36]

The car runs a bit hot and I'm wondering if this could be the cause as it means that the radiator is effectively not pressurised.

The radiator is still pressurized if you have a nomal radiator cap, the Lotus overflow system (the bottle) is not pressurized and works on an expansion/contraction system through the overflow pipe, all the pipes must be a good fit or the system will not work
I do not like the system and have fitted a non pressurized radiator cap and a pressurized tank with pressurized cap (the type that was fitted on the old Mini/1100 range)
As the water expands it fills the tank(which is half full when cold) and returns to the radiator as the water cools keeping the radiator perimently full.

[tyasman]

thanks to all