I read that modern fuel injected engines should not be started early and allowed to warm up on cold frosty mornings as the engine pumps extra fuel into the cylinders which act as a solvent against the normal engine oil lubrication. Why is extra fuel pumped into the cylinders, and why does it only happen when the engine is idling first thing? Does it also happen while sitting at a long traffic light or when stuck in a traffic jam?
That is wrong. I don’t know where you got that info, but it is wrong. You don’t need to warm up modern engines because the oil they use is FAR better than 40 years ago. Has nothing to do with the fuel injection. so your followup questions are moot.
The person that told you that is confused. On modern cars everything is constantly monitored by the sensors for optimal efficiency.
The air/gas ratio will vary according to the engines need. The only harm is to you fuel mileage.
On carbureted engines that was a possibility if the choke did not open correctly.
Yahoo had an article yesterday that warned of causing damage to your cylinder walls by warming up your engine on cold mornings because of excess fuel as I stated. They didn’t go into detail about why the engine would do this only when it was cold, so it didn’t completely make sense, but it was on the internet, so it must have been true, right? ;~)
I can make a case for some short warm-up with my 2.5 liter Nissan Altima engine.
If I start it when cold outside (under 30), and immediately start going, valves rattle like crazy since CVT revs the engine up to 2500-3000 for any reasonable acceleration to happen.
If I’m to get to 50 on the parkway next to my home and merge into the traffic with a bearable 2000 rpms or so, I will be honked at and blinked at with all other cars.
The alternative of letting vehicle idle for around 2 minutes while I’m scaping the ice from the glass and such gives it just enough time for the timing components to warm up and not to give me a heart attack.
This car is 89K miles, and it was doing it from the new.
Lately I hear one of the valves a little bit on the noisy side until warned up, but I can not convince myself to get camshafts removed only to adjust the lash.
Personally, I do warm up my vehicles for 30 seconds to two minutes. Only when it is below about 20F. I also never scrape ice off a window. If I have ice there, I let the car warm up till I can clear it without scraping. I have damaged a couple of windshield with plastic ice scrapers in the past. I’m a car-centric person, so I have (unheated) garages, but in some cases (airports in winter) I will wait a while till I can clear off the ice. My older Highlander does no like the cold anymore. It definitely gives a vibe that says “Give me two minutes” on the coldest mornings.
I had to commute on the road which was under construction for 3 years or such, so my windshield is so pitted by sand, that I can barely find a spot to make a fresh scratch 
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My 1979 Toyota 4X4 had the cylinder wash-down problem at least one winter before I figured out the choke and fast idle and AAP systems. The amount of oil in the crankcase went up - it was actually oil plus gasoline and you could smell it. That scenario does not happen with modern fuel injected engines.
But warming up by idling is in my mind a cost - to self and to environment - with little or no benefit. Start up, put on seat belt, drive away gently for the first block or two - more if it’s below about zero F. It’ll warm up faster and you’ll get less water built up in your exhaust system.
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“Warming up” has different meanings to different people. Anywhere up to a minute or two, I did that in cold (Anchorage) weather to get the oil flowing, I’d then drive with a 3000 rpm limit on my GTI until I felt warm air from the heater. Others think of “warming up” as getting heat out the heater, which is not at all needed, in my opinion. But does it hurt? I doubt it with modern engines.
Friend had a '74 Cougar, he wondered why his oil smelled like gasoline in the winter (he could even light it with a match). I think it was a combination of carb problems and worn rings.
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I live in an area with a cold, snowy, and icy winter. I start my car early to help clear the front windshield and to help melt ice on the windows and make scraping easier. Most mornings I can’t start driving until I have heat in the engine because the windows won’t clear and I can’t see unless the defroster is blowing warm air. To avoid shivering in my car and waiting for the heat to come up, I start my car five minutes early and then turn on the defroster when I am ready to go.
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Letting the engine warm up by idling doesn’t warm up the other lubricated parts of the vehicle. That’s why it’s prudent to drive gently the first few miles.
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The fuel air mixture is made much richer in a cold engine as some of the fuel more easily condenses out of the mixture onto the cold intake manifold. In times past, this duty was handled by the choke. The PCM is in charge of that now.
I’ve been warming up my Corolla’s engine 3-5 minutes for 27 odd years every morning before leaving and never had any gas in the oil problem yet. I don’t think that’s an actual problem. The reason there’s more fuel injected on cold starts is b/c the engine won’t run well unless the fuel/air mixture is enriched until the coolant temperature reaches normal operating temperature. I doubt idling takes any longer than driving to reach the final coolant operating temperature, may take less time. So there’s more gas being injected on and immediately after cold starts whether you are idling or driving. What’s probably true is that warming up the engine w/modern fuel injected cars offers little to no actual benefit to engine life or performance. So its a waste (albeit small) of gasoline. I do it mostly by habit, and in the winter b/c the heater is working better by the time I get ready to shift into gear & go.
The only reason to warm up the engine is to clear the windows on a very cold day. Modern engines with synthetic oil in them will have oil flow to the valve gear in less than a minute and without a carburetor or choke you can drive right off. I would not try rapid acceleration or very high speeds until the engine has warmed up.
It was a warm 27 here this morning, minimal frost on the windshield, so I started it up, gave it 15 seconds, put it in gear, then drove off gently. I rarely let my car idle in the cold just to warm up anymore
Yeahhhh, there are lots of people writing “articles” on automobiles that have absolutely NO clue about them. They are often interviewing people with no clue as well. To a “journalist” writing about cars, a guy that works at a tire shop or a quick-lube place is an “automotive expert.”
Even IF the “journalist” speaks to an actual expert, it becomes much like trying to teach the pet dog calculus. He may cock his head to one side and nod, but he doesn’t understand any of it!
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Yahoo is full of clickbait articles all the time. They also do not seem to police their ads very well as I see lots of malware and scams come in through their links. Google is much better about taking out this digital trash. I remember one where they had the worst engines ever made and they didn’t even mention the Chrysler 2.7L or Ford SPI. They actually mentioned some that I am familiar with and although underpowered for most people, they are solidly reliable. It seemed like more of a cool factor was involved than actual reliability of the engine.
I might let the engine run for 10-15 seconds before going on most days. Basically I start the car and get into my seat belt. Now when it is EXTREMELY cold I might give it a few minutes but most of that is for my comfort and not the car. Remember that many cars are coming with 0W20 oil these days and it flows well when cold.
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I’m not sure why everybody is so obsessed with a question if oil will flow right off the bat or not.
For 99.9% of modern oils it will, end of story.
As you start driving that cold engine and you might need to use more than 10% of its power, that’s where things turn ugly, at least to some engines, just listen to the sound of the timing working like a bunch of small sledgehammers.
It’s not that they should not it’s that they don’t need to be
All engines require enrichment when they are cold for the reasons stated above. Back in the day a mechanical choke performed this duty and was not as precise as modern fuel injection with feedback control. So there is almost no extra gas to wash down the cylinder walls as there was “back in the day”. Old advice that has no merit today…
The enrichment only happens when the engine is below operating temperature. It is gradually reduced as the engine warms until no enrichment occurs. Rings seat/seal better with pressure so that’s why it is preferred to start the engine and proceed to drive almost immediately to minimize combustion blowby and to more quickly get the engine warmed up by doing some work. Modern oils at the recommended viscosity will provide more than adequate protection under these circumstances. Of course, you should drive conservatively as the engine warms up. I start my engine and by the time I have my seatbelt connected, I’m putting it in gear and driving off. No warm up time whatsoever…