> I'm aware that blocking off radiator air might not help, but it's free and
> easy to try, so why not.

Errr... because it's already been determined that the radiator is not
getting any circulation at that temperature and is not the issue?

Reminds me of the old joke about dealership service techs:
(company) = GM, Ford, VW, Dell, Verizon, or whichever company you've had bad
troubleshooting experience with

How can you tell a (company) service tech who has a flat tire?
He's changing the tires one at a time to see which one's flat.

How can you tell a (company) service tech who has run out of gas?
He's changing each tire to see which one's flat.

--
John Bange
'90 Vanagon - "Geldsauger"