The Libra has a small bore hose from the radiator to the expansion/header tank. I believe it's to reduce the chance of air in the front of the cooling system.
Is this actually necessary? The Elise and MGF don't have one of these and they obviously don't need one, so why on the GTM? The front outlet for this hose isn't at the top of the radiator so I can't see it being that much help.

Hi Nik.

Not sure which radiator you have.

The one fitted to my car by Mathew prior to my ownership is from a VW Passat, and the bleeder/expansion tank port is uppermost, above the top hose port.

However, unlike either a Metro or Passat, this isn't the highest part of the system in the Libra - the heater hoses and heater matrix are, so it would make more sense to bleed the system here if that is what you mean.

Can't comment on Elise or MGF.

Phil.

That hose is there cos that's how GTM said to do it in the build manual. The metal pipe it comes off of is a metro one that normally runs across the top of the radiator so any air trapped in that part of the system (on a metro) escapes to the expansion tank.
It's supposed to serve the same purpose on the Libra but the positioning of the take off is lower then the top of the rad so not ideal. Also the fact the air has to be pushed down and under the car to get to the exp tank is maybe not great either.

All this only applicable with a metro rad.

I modded the hoses in that area so the take off is above the level of the rad top. I have a tap in that line at the tank end so can switch off that return leg. I left the hose in place cos it's useful to pump coolant down it when filling/bleeding to force air out of the system.

I think The answer here is that the hose probably isn't really necessary.
The reason I ask is that I'm planning on using a header tank with 2 inlets (as opposed to 3) so dispensing with the hose in question would be helpful.
I just wondered if anyone else has got rid of it?

Yes, I originally ran mine with the return pipe back to the header tank. I removed it a while ago and shortened the pipe to just act as a breather when refilling the system. It didn't make any difference to the cooling so my conclusion is that it can indeed be taken out.
Nigel

Thanks. I’m going to remove mine when I fit the new tank with level sensor. Makes the job a bit more straightforward.