big trucks do it in the winter time ...(ignore the joke line...) to get heat at all. on long drives through the mountains and such, their HUGE radiator is such a giant heat sink, that even with the Tstat closed, they get little to no heat. our radiator can do the same thing, but covering it will not really help noticeably the warm up time. and DG's tip is there to help COOL down an engine. so also not an option. if you have a good tstat, and your fan clutch is disengaged, your car should be putting heat into the cabin in 5 minutes of idle. if it is REALLY cold (sub zero) dropping a cardboard sheet between the condenser and the radiator could help speed up the warm up time, but I don't know if it's worth it or not, and don't forget to remove the cardboard before you drive, or use a laminated cardboard sheet and cut a 6" or 10" square out of it and leave it in all winter, but keep a sharp eye on the temp gauge.
try it and see, then let us know how it works.
John

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!