Driving a car while cold is not a very good way to warm it up , it is however as the governments, enviromentalists, and car manufacturers of the world decided a number of years ago , a great way to conserve fuel and reduce air borne pollutants (in this it has done a stellar job, in the last 20-25 years this recomendation has probably saved us an ocean of fuel).

However the automotive engine ( basically unchanged in the last century ) is still made of metal and still a slave to the laws of physics.

When manufacturing or rebuilding an engine , the specifications allow for heat expansion (operating temp). When running cold many of the internal parts are slapping around in there until the heat expansion brings them up to proper fit ( if parts were cut to fit cold, the engine would sieze upon warm up).

Driving on a cold engine can lead to increased piston skirt wear, cracked pistons, out of round bores (sometimes requiring drastic over-bores at rebuild time hence shortining the service life of the block).

If using regular oil , when cold it has a tendency to foam. When put under load this foaming oil has a reduced film strength , and can allow metal to metal contact , in extreme cases it can lead to spun bearings.

While driving with a "light foot" until it reaches operating temp, as my manual says is a nice idea for some , in reality many people have to stand on it just to get out of their driveway with fenders intact.

True a proper functioning system will minimize water vapours in the engine, but if it never gets warm long enough to burn them off, thats where the sludge comes in. It's cumulative and once it reaches the sludgy form it tends not to burn off as well.

While I wouldnt use a winter front (ok bra with grill restriction for you sports car fans:-) in moderate climate, but in extreme cold a cover on the front (with a permanant opening in the area in front of the fan clutch) is a perfectly acceptable way of speeding warm up, maintaining under hood temp while making stops about town, and preventing radiator freeze up. In extreme cold climates,( no I'm not talking Bakersfield California cold, more like Billings Montana cold:-) this arrangement properly used (yes pop it off on the hot days) will not lead to overheating.

-----Robert