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Comment by alphabettsy | Hacker News Reader

> Remember that a lot of people have to spend 10-15 minutes warming up their cars before they drive them in cold weather.

People choose to do this. This isn’t required and it’s recommended against in modern vehicles.

> I do not want to go into details, better car mechanics than me should, but there is all kind of chaos that can happen if your engine freezes and you try to drive it immediately.

Engines do not freeze in the conditions common in most of the US, even with winter like we’re currently having. The engine coolant is a mixture of anti-freeze and water.

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> People choose to do this. This isn’t required and it’s recommended against in modern vehicles.

I’m curious about that recommendation, do you know why that is?

Because it’s much more efficient to heat up a modern car by driving it than it is to let it idle.

You need N joules to heat up the 300kg of the engine. It doesn't matter if you sit there for 15 minutes freezing your ass with an engine running at 1500rpm (and all other car parts still freezing) or 5 minutes actually driving at 3000rpm - you still spent N joules on heating, difference is the time. And the car heater runs on the engine heat, not on the electricity, so the sooner you would warm the engine the sooner your car interior start to warm and stops seeping the heat from engine.

It's actually more importantly to have enough viscosity in ATF, but again, the sooner you would go the sooner it would warm.

It's possible you need to idle for 10 minutes just to scrape the ice off your windows though :)

You don’t need to idle the car for 10 minutes to scrape the ice off. You can scrape it off with the engine off.

For the good of the engine maybe. For the good of the driver... when you're finished scraping off it's better inside. Plus the windows kinda warmed up so it's easier to scrape.

Not sure what is the assumption. I have the opportunity to scrape the ice off of the car many times a year.

Depends on the weather. There were a multiple times when the running engine heating up the windshield was the necessary prerequisite to scrape the ice off.

Its just that I care more about my comfort than wear on the engine

I've definitely had a serious enough layer of ice on the windshield that my nice scraper was an exercise in futility. Maybe 2-3 times a year, but it's a thing.

> I’m curious about that recommendation, do you know why that is?

I was always told (since the 90s, anyway) that it's better to drive off slowly with a cold engine and let all the components come up to operating temperature together than to drive off with a hot engine, and cold gearbox, driveshafts, tyres, etc.

I generally let a cold engine (i.e. overnight) idle for maybe 30s before driving off slowly, and it reaches operating temperature in about 5m or less.

Because your car engine does not get the right mixture until you start driving.

In a 2022 car I have now even the cabin doesn’t get proper heating from the aircon until it’s driven.

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