Being an air-cooled engine, the 2CV needs to remove heat from the engine bay. It does this by having a pair of heat exchangers that take warm air that has cooled the cylinders and passed over the exhaust and direct it out under the wings (or into the passenger compartment for heating).
To get the air from the heat exchanger outside the engine bay there are short cardboard tubes that fit through a rubber grommet in the wing.
However, these tubes don’t age well, especially if they’re exposed to the wet – which is highly likely under the wings. As a result the round tubes no longer grip the oblong heat exchanger outlet very well and the hot air will escape into the engine bay.
To remedy this Burton 2CV parts do a rubber heat dump-off tube that fits both the hole in the wing and the heat exchanger.
Fitting is a very easy job if you have the wings off and I suspect it would still be pretty easy with them on.
First remove the old cardboard tubes and the wing grommets. The smaller flange of the old grommets is on the outside of the wing so they’re easier to remove towards the inside.
The new rubber tubes have the grommet as an integral part but the smaller flange is on the inside of the wing so they need to be fed in from outside. A small amount of silicone grease (not petroleum based lubricant) between the flanges makes mounting easier and will protect the metal in what could be a water trap.
They should be mounted so that they point downwards.
When the wing is refitted to the car the oblong end of the tube fits securely on the heat exchanger outlet and the accordion section will help absorb vibration to prevent the tubes becoming dislodged.