Jim;

I'm sure that material works well to attenuate noise. Unfortunately, ANY sound deadening material will also thermally insulate the hood and keep it from exchanging heat from underneath. So it's somewhat of a dilema...but just think about a modern engine compartment...I don't think if you dropped a tennis ball in there it would make it to the ground...on the other hand, in a 122 (or 1800 for that matter), I (jokingly) say that a basketball would...point is, there's a LOT more air-space in there which will cool the works...yes, in turn, the air will get warm in the process, and will get trapped under the hood at the firewall end (but I bet the temps are nowhere as high as a modern car with a cat. near a stuffed engine bay!). But I believe you have the perfect solution...that electric fan! When driving, the air moving through the radiator exits under the car...so in addition to a cooling system temp sensor, and your manual switch to control it, I suggest you install another temp sensor back at the fuse block area which can also turn that fan on...I think just the fact that you're moving some more air after vehicle is parked (which will also exit out UNDER the vehicle...and aroud the unsealed edges of the hood) will be fine.

Under hood temps in ALL cars creep up after parking...thats one of the reasons you get a heatsoak and it makes a hot start difficult...especially in an SU equipped car (plus, they're sitting right above the exhaust...and that little shield only blocks so much). Some Jags had a battery venting (cooling) fan because of this very problem...I guess the battery was located at the firewall not unlike a 122 or 1800 and they were experiencing (cooked) battery failures. I have seen some 122s with totally louvered hoods...this is obviously a big decision and it's not stock, but, just a couple louvers would certainly be enough to convection vent the heat significantly and make a huge difference.

Bottom line IMO: Move some air under the hood after the car is parked, preferably thermostatically controlled, and I think you'll be fine. I for one will definately NOT let this keep me from insulating under my 122 hood!

Cheers