[Christ]

That blanket is primarily to keep heat from escaping during the rising expansion of air volume.

Underhood areas aren't necessarily "drafty", though they're obviously not sealed. The blanky holds more than one core purpose, based on those facts.

We could find it safe to say that while the blanky is somewhat effective in holding heat into the engine bay, it's more effective at reflecting the rising heat, and thus is used to protect the paint on the hood of the car from damage due to heat soak. (Talk to carbon fiber hood guy... he can tell you)

A second use would be to help deaden noise and dampen vibration of the thin sheet metal of the hood, which causes further noise. Again, not the prime use, but one of the many uses.

So, those things said, and any other uses considered, the original poster's question was "will it be helpful to retain heat by putting a blanket on my hood". And the answer is still "no, it is more trouble than is necessary, and you'll face alot of stupid looks on your way back to the car."

Ford Man - I find it amusing that both of your fuel logs show close to the same mileage per gallon, yet based on your percentages above EPA rating, obviously the older car had a higher efficiency rating...

Is there a reason that auto-makers are allowed to continue saying that efficiency has improved since the 80's, when it so obviously hasn't?

C'mon.. since when is 30-40 MPG a landmark of efficiency? I've never gotten less than that in any small vehicle I've owned, including my trucks.