inner outer preheater hoses

[whizbang]

Howdy gang,
I have a a newbie question on preheater hoses on a 69 911E. It looks there is only an inner hose on the car now, with small hose clamps to match. I ordered inner and outer hoses from our host, but am not sure how to mount them. Does the inner just slide inside the outer and a single large clamp go on the outside of them both? Thanks for your help.

[whizbang]

I may have an answer to this. On further research and some more crawling around under the car, I spotted a hose that runs from the front of the left heat exchanger to a pipe through the bottom of the car. The other end of that pipe has the hose that runs to the thermostat. My guess is the latter hose is the inner hose (inside the engine compartment) while the former is the outer hose (outside the engine compartment).
Is that correct?
In the pic below, is the hose above the left side heat exchanger and lower valve cover the outer pre-heater hose?


If so, the style of the outer hose is very different. My current outer hose is thickly padded rubber (neoprene?), while the new outer hose is just concentric paper and foil.

Also, the new inner hose, (also concentric paper and foil) has a slightly larger diameter than the old inner hose, which while it was paper and foil seemed covered in almost a plastic finish.
Inner pre-heater hoses; new on left, old on right:


Any problems with using this somewhat larger diameter for the inner pre-heater hose? Is that plastic type finish important?

Thanks for your help.

[Rot 911]

First the inner preheater hose slides inside the out preheater hose and that is the hose that connects to your MFI thermostat. The hose underneath should be made out of rubber.

[whizbang]

Thanks for the response. My existing (40 year old!?!?!) hose was only a single, although it did have a plastic like finish on the outside. So the hose to the thermostat is actually a double hose, one inside the other. Interesting. Any idea why they do that?