steamedturtle

There is a lot of anecdotal evidence across this forum and across the internet about warming up your car in cold weather, driving short distances, idling the car and the like. What I'm looking for is a technical description of what happens in certain specific scenarios. I know that I can probably put all this out of mind and drive as I normally do and everything will be just fine, but being the curious and obsessive person that I am, I just cannot put it to rest right now and desire a technical explanation of whether or not to do A or B in different situations.

1.) I do know that idling your car is not great for it and can lead to carbon deposits and that it is pointless to let your car "warm-up" by letting it idle for a while before driving it. So I generally get in my car, turn it on, set the air and fasten my seat belt. By this time 30 seconds has passed and the oil has circulated, for lack of a better word and I start driving gingerly (don't rev above 4k / gentle throttle inputs) until the car has completely warmed up.

Say for example I'm picking up someone 1.5 miles away and when I get there it is a 5 - 10 minute wait before we are on our way. The car and engine will retain most of its heat in 10 minutes, so I suppose it is best to turn off the car for the 10 minutes while waiting. Logically, this makes sense to me. Technically, what exactly is going on with the engine?

2.) What's the difference between driving 3 miles and 30 miles, especially in sub freezing weather? I have heard someone people say that if you make a lot of short distance drives you should mix in a half hour joy ride because it will somehow "repair" some of the damage inflicted by the short drives. What's the deal with this.

3.) My car warms up much quicker than my previous car (8th Gen Civic) according to the engine temperature gauge on the dash. I can drive 3 miles in thirty degree weather and have the temperature gauge be at normal operating temperature. Based on the answer to question #2, does this mean the car has driven a "safe" distance and is safe to turn off with minimal engine wear?

Thanks for looking. If I think of more, I'll post it, but I think these are the questions I've always wondered about.

zeroptzero

I don't know about answers to all of your questions but here is my opinion, not saying it's right but this is what I follow.

Firstly, in really cold weather there is nothing wrong with warming up the car IMO, it is wasteful of resources, but I don't like the sound of a cold engine with piston slap in very cold weather and trying to drive to keep rpms low for the first few miles. We regularly see -10 to -15 degrees Celsius in winter months here. In warmer climates minimal idle for sure. I think excessive idling can introduce fuel dilution to the oil due to richer a/f mixtures and some people think the low oil pressure at idle is worse than higher pressure while driving.

The vast majority of engine wear occurs at start-up, and cold start-up is the worst. Oil flow to parts at start-up is critical. Once the oil is up to hot temp and you are cruising down the road at light load there is almost zero wear occurring in the engine. It takes about 20 miles of driving to get the oil up, this is not the same as coolant temp and bars on the temp guage, it is the temperature of the oil. Hot oil burns off impurities in the oil so it works better in the long term when you can make trips of 20 miles or more,short trips are worse because the oil doesnt get hot enough. If I was picking up a friend in really cold winter temps I'd leave my car idling if the engine isn't fully warmed up to avoid one more cold start, if it was fully hot I'd shut it down.

SpitfireS

IMO:

1) That's the best you can do.
Idling from a cold start is also bad for the transmission as the oil pump does not pump when you're not driving.

To answer your question: I would also turn off the car, even after 1.5 miles after a cold start.
Maybe let it idle a bit in freezing weather, but not for long.
Idling is idling, low load, low fuel consumption, not much energy to warm up the engine.

2) Every car runs rich(er) when cold, even with an ECU.
More fuel washes more oil off the cilinder walls, during the inlet stroke.
A rich fuel mixture burns more easy but also doesn't burn completely.
So you get more unburned or halfburned fuel > all kind of nasty chemicals and water too.
They will be neutralized and contained by the oil.
Once the oil gets warm the unburned fuel and water will evaporate.
Its not that you regenerate the oil, because those nasty chemicals "use" some of the additeves, gone = gone.

The rest is simple: on a 3 mile trip you're running richer for (lets say) 1 mile = 30%
On a 30 mile trip you're running richer for 1 mile as well but its only 3%.
And on a 30 mile trip your oil will get really warm.

3) The F20/F22 has an oil-to-coolant heat exchanger, so the oil will warm up quicker that on cars without.
Because most wear is at start up, the damage is done, now way to repair that by driving longer.
No start = no wear = rust

What does help is using a true syn 0W-30 oil.
Its much thinner when cold and will flow faster through the engine.
I've been using 0W-30 for 3 years now and noticed a real improvement during a cold start, coming from a 0W-40!
The engine runs much smoother from the start, in any weather and temp.
Don't forget the 2000 rpm cold start peak.