I don’t know the maximum permissible temperature in traffic, but…
There is a product called WATER WETTER, by Red Line. It’s a
fluorescent pink fluid, a pint of which is added to the coolant. It
mixes well with anything you’re likely to have in the system, and won’t
damage seals, aluminium, etc.
The product simply changes the specific heat and thermal transfer
characteristics of the fluid in which it’s dissolved. In my experiments,
I was able to generally improve the cooling of my race car by a
substantial margin, and was careful to isolate the action of this
product while making measurements.
My Mk I has a 4.2 fitted, and it can run quite hot. There’s no
thermostat (very mild climate here in San Diego). I added WW, and under
carefully measured identical conditions achieved a 20 deg F drop in
system temperature.
I expect it’s an internationally distributed product, and available
through specialty shops in most markets.–
Henry Eisenson
Introtech LLC
6336 Greenwich Drive
San Diego, CA 92122
(619) 453-7600, fax 552-9050