I would like to put my two cents in - do with it what you will.

In my experience and knowledge, the warm-up period is to get body fluids of your car running around...specifically oil into the engine. Think of it like this:

You warm your body up before running to get the blood flowing so you don't get muscle cramps. You drink water to accomplish the same thing before and after warming up/warming down. Your car works the same way.

If your engine runs without oil, it will get too hot and friction will cause damage (metal to metal). The warm-up period is to get oil into the cylinders of the engine. When you check your oil level, you do it after your car has been sitting a bit. That's because all of the oil is now out of the engine and in the oil pan. So, the warm-up period is to get the bodily fluids running around in your car so as to not cause damage. That's what the oil pump does - delivers oil into the engine. The water pump (hence water getting into the engine straight-away) isn't as important. Tranny fluid creates pressure to change gears. The warmer the fluid, the better the car changes gears, and the better it is on your tranny. Also, the tranny fluid drains from the gears, and when you warm up the car, it causes the fluid to start running around in the tranny as well (although the tranny fluid depends on the tranny being in gear to effectively move the fluid).

Anyway, that's my take on it. Warm-up time (at least 2 to 3 minutes) is essential for lower engine wear, whether it's summer time or dead of winter.

 

With older motors, the need for a warm-up was actually a necessity to prevent pre-mature wear. The older motors had lots more clearance between parts and due to them being made out of slightly different materials, the gaps could get rather wide (relatively speaking, we are talking on the thousandth's of an inch scale here). This could lead to excessive play and parts slamming into each other. By letting the motor idle, you are letting things warm up, expand and tighten the tolerances. With the modern day motors, things are built with much tighter tolerances and therefore the amount of slop in the engine is minimized. This is one of the reasons why motors are lasting so much longer these days. So, the need to let the motor sit until it is up near the normal temp band is no longer needed. But, with that being said, it is a good idea to atleast give the car a few seconds (say 10-15) to sit there and idle to allow the oil pump to get lubrication to all vital parts. With the colder temperatures, the oil is thicker, therefore doesn't tend to flow as easy and will take longer to get to the furthest points on the engine (ie, main bearing next to the tranny and the cylinder 5/6 lifters). By letting the engine idle, the number of movements of these items is minimized.

So, the need for a long term warm-up is no longer needed, but a short fluid movement time is needed. In warmer temperatures, the time needed to simply start the car, put it in gear, check to make sure all is good before moving is more than enough time.

 

I just warm it up so I don't shiver the first 20 minutes I'm driving waiting for the heat to kick in, which seems to take a while in my S-Type, but once it gets heated, it works fine. Having my bum warm in the meanwhile sure helps.

 

Well, as someone who also lives in the -50C climates I can say that as long as the car has been plugged in, all is usually well and it takes about 30 seconds or less to warm it up. Once the rpms drop from the inital 1200 or so at start up down to around 800, the car is ready to go. Any longer is just for my comfort! Now, for those mornings when I forgot to plug the car in and it was left outside and dropped down to -45C that night, I have to let it run for a few minutes until all the yelling and squealing stops! At those temps even the best oils need some time to warm up if the car wasn't plugged in. I also find that after about 5 min of driving, there is heat comming out of the vents and I can start to feel my limbs again!

 

Ya, I know that one. I find it easier to let my passengers just wait inside the house though.

 

When the high Idle comes down it's time to drive slowly for a short distance and then drive normally.

 

The Jag will warm up while driving. I took a shop class for fun one month and the specialist with 30 years experience told us that "warming" up the car does nothing other than damage it. Fluid flow and such are not optimal while idling.

 

From website of the Car Talk Radio Show on PBS:

Briefly:

1. Your engine warms up quickest with some load on it, i.e. driving it.
2. An idling engine runs very inefficiently and pollutes more than a loaded one. In addition, your are not moving while you're idling; causing even more waste.
3. The fuel/air mixture during idling is not the best for maximum engine life; raw gas washes the oil off the cylinder walls.
4. If you warm up the engine first, than take off fast, you are putting incredible strain on the other components of the car that are still cold. Taking off shortly after starting warms up the whole power train and suspension together.

In spite of the (4) points, you need to idle the car long enough to get the engine oil to circulate to the valve gear on top of the engine. In most of the US, with 5W30 oil this takes no more than 20 seconds or so. If you start the car, belt yourself in, check mirrors, you should be ready to take off gently and when the temperature gauge is half way to normal, you can blast off.
In all cases, make sure your windows are clear before taking off.

http://action.publicbroadcasting.net...st/669811.page

 

Remembering of course that the temp gauge needle is only registering the temperature of the coolant not the engine or transmission oil temperatures.