Step 1...
Coroplast blocking plate over existing custom-sized grille opening. Note actuator linkage leading to cockpit.
Step 2...
Monitor coolant temperature while under way. At desired temperature, manipulate actuator.
Step 3...
Step 4 ...
(simulation)
Step 5...
Et voila!
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Notes:
1) Best suited to convertible or sunroof-equipped vehicles.
2) The first time I pulled the rip cord, I was going about 50 km/h (30 mph).
Too fast! It flew over the cockpit and almost snapped the actuator linkage! Next time I tried around 15 km/h. Still too fast!
3) You don't want to be too concerned about the finish on the aft end of your vehicle -- the grille block will bounce & flap around back there before you get it reeled in.
Despite the silliness, it works. Speeds warm-up time, and improves aero. It was used on the last part of my recent record tank:
53 MPG tank in 1990 Mazda Miata: personal best (4.5 L/100 km)