Please, warm your car up in the winter, despite what you may have recently heard in the press. Here’s why.
Metals expand and contract at different rates, based on temperature. Aluminum, for example, contracts about twice as much as steel at low temperatures. This means that crucial tolerances, like those between your crankshaft and bearings, can be VERY tight at low temps. Does your car turn over slowly in the winter even with thin oil? It’s because your engine is basically almost seized as some parts have contracted more than others.
You probably also have aluminum pistons in steel cylinders, which expand and contract at very different rates. At cold temps, your aluminum piston will contract more than the steel cylinder, creating a larger than normal gap between your pistons and cylinder walls. Do a compression test on a cold engine and you’ll see what we’re talking about.
What’s worse is that your pistons will expand much quicker than your cylinder walls and block, because the pistons are small and light, and the block is big and heavy. This means that your pistons will be at full size, and the cylinders that they travel in will be smaller than normal. There is a window of time when your pistons are warm but your block is still cold, and revving or putting load on your engine while it has these extra-tight piston clearances isn’t good for anything.
Your engine block, heads, crankshaft, cylinders, pistons, piston rings, camshafts, valves, bearings, etc are all made of different metals that are effected very differently by heat and cold. It was designed with a reasonable operating temperature range in mind, and we as drivers need to respect that and avoid driving outside this temperature range whenever possible.