The above clip comes from the YouTube channel Engineering Explained which does exactly what it says on the tin. As the guy in the video explains, you don’t actually need to warm up a car’s engine before driving if it has electronic fuel injection, which automatically compensate for temperature changes.
In fact, it could actually have a detrimental effect on your engine:
Cold [fuel injected] engines run rich to compensate for poor fuel atomisation. This means extra fuel is injected into the combustion chamber.
Now fuel is a solvent, so when extra fuel gets on the cylinder walls, it washes away the oil from the cylinders and pistons. Less oil on the cylinder walls means less protection, and because the oil is cold it makes it harder for it to be replaced. This means the longer you spend with your engine cold, the more wear you’ll have. Idling the engine doesn’t put much heat into it, so the car remains cold for a long duration.
If it’s cold outside, you can wait 15-30 seconds to ensure that oil is flowing, but you don’t need to wait for the engine to be warm. It will heat up faster by driving the car lightly. By heating it up faster, the oil gets to operating temperature more quickly, and this is what you want to prevent wear. If it’s really cold outside, the time it takes to scrape off the windows so you can see will be plenty of time for oil to start circulating, so you can get in and go once you can see out the windshield.
So the next time you’re stuck in the passenger seat of a car freezing your arse off while the driver warms up the engine, politely explain to him that he’s probably doing more long-term harm to the engine than good.