Guess I am lucky I have a Polar White xB because the 1/2 thick white packing foam blends right in with the front bumper - couldn't take the low engine temps any more so tonight in 45 minutes I blocked off the entire front grill two openings top was 3 fingers high the bottom 4 fingers high and about 4 feet wide each - both now completely plugged with pressed in slightly larger than the opening strips of white foam. Test ride 9 miles 39.5mpg in 19 degree air intake temps engine peaked at 190 degrees on a modest uphill to a stop sign with heater on recirculate low fan. It then dropped back to 186-184 degrees and still gave plenty of heater heat - much more than usual without dropping the engine temp like it did today before the block install when it dropped to 150 from 158 while driving. Nothing but the springyness of the foam holding itself in the opening of the bumper. Next will be the hood to grill foam sealing to keep more heat in the engine compartment and prevent spray and junk from entering the engine compartment. One advantage of the grill block is it protects the radiator from flying rocks and sand during the winter. Next higher speed runs and mileage checks at higher speed. Outside temp according to weather is 10 degrees.
I am not sure where to commonly get gaff tape. I work in a theatre and we use it here and I bought two rolls from the theatre when the theatre bought a case. I would think any theatrical supply place or maybe even musicians supply place if they have band gear as well. I didn't look on eBay, but they seem to have everything else It is $12 a roll when I bought it so it's pricy.
I honestly thought it might not hold up being on the front in winter, with the salt and car washing and all, so far so good.
Gaff tape is a great idea. I'll have to dig out that roll I bought a while back from a pro photo supply store.
Reality is merely an illusion, albeit a very persistent one. - Albert Einstein