Gripenfelter

Many moons ago...

Back in the days of the carburator, there was a law that people lived by. And it said...

You must thoroughly warm up your engine before driving the car.

This law was deeply rooted in poor vaporization of the gas in a cold carburator and intake manifold. It was accepted then that it was best to warm up the so as to eliminate hesitation, stall, or throttle tip-in sag. While this scenario may have served the driver well, it was the worst possible scenario for the engine.

A cold engine experiences excessive wear due to the rich mixture required by the EFI system. This tends to wash fuel from the cylinder walls and aggravates wear between the rings and cylinder bores.

This driver believes that one should limit the amount of cold running time and accelerate the warming process. This can be done by driving the car at light load as soon as the oil pressure comes up to level.

An engine that is driven immediately will have much higher coolant and oil temperatures than one that idles for 5 minutes. At the same time you will also warm up the rest of the drivetrain like the transmission and wheel bearings. Something idling can not do.

What do you think?

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John98R/T

As a kid i was always told to let your car warm up before driving it, but of late my outlook on cold weather driving has changed. I believe that as long as you dont turn your car on and drive it 70mph as soon as you leave your driveway youll be fine. Car manufacturers dont tell you, "now every day before you drive let it idle for ten minutes" i dont see a real problem with driving your car cold, as long as you dont hot rod it until you engine temp is up to regular operating temp. i could very well be wrong, but its a fact cars break, and every once in a while you have to fix them. As far as cold starting and idle time go i dont think there is a huge effect on your engines performance as long as you drive like a normal person in cold weather. Simple stop and go traffic is much worse on your engine than cold starts.
Peace....
:flash:

JD@af

Sounds good. I have been unsure about this for years, and often believed it best to air on the side of caution, and drive your car less as opposed to more before it was fully warmed up. I have followed the rule of waiting for the coolant to come fully to temperature before driving your engine hard, but it seems this only address part of the picture. Thanks for the insight.

i_rebel

I don't know if there's any real value in doing it . . . but I try to do so religiously. At least when I'm not late for work anyways . . .

John Napkintosh

I do it. Rapid changes in temperature cause materials to expand and contract, and warpage can occur. Whether or not this is happening to a large enough degree to cause permanent engine damage is another question, one for which I have no answer.

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Gripenfelter

Unless you are racing as soon as you start the car, I'm sure you're fine.

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sq_man

You are absolutely correct. Slowly drive the car to warm up the engine as quickly as possible.

The worst thing you can do with a modern engine is sit there idling.
There is no load on the engine so it is producing little heat.

I have a 2001 BMW 325i which has a technology called "engine mapped
cooling". This means the engineers include in the ECU an analytical/semi-empirical mathematical model of the heat transfer within the engine. It is basically a super-thermostat. The ECU uses information from various temp- and flow-sensors to adjust the parameters that affect an engine heating: coolant flow, richness of the mixture, etc. This is all designed to heat up the engine as quickly as possible. Pretty clever. Damn they are good engineers.

Don't worry about parts heating up "too quickly" as mentioned above. An engine's thermal mass is quite large and it is designed for thermal shock in the pistons. (ie burning fuel) Though thermal stresses are a real problem when not managed properly (puring hot coffee into a thick glass) an IC engine is designed to handle it.

ivymike1031

I figured I'd chime in with the "no warm-up" crowd - warming up just puts more hours on the engine, and doesn't get you anywhere. I also agree that you should keep the revs down until the engine warms up a bit. Piston - liner clearance (and thus piston secondary motion) changes significantly as the engine becomes warmer. Some valvetrain configurations (but not all) will also have much higher lash under cold conditions than under hot conditions (especially in cold weather), and thus dynamic control of the valvetrain might not be there for ya if you rev it up cold.

CharlesW

Little or no warmup has been my procedure for years. Several of our cars have exceeded 150,000 miles following that guideline.
The warning to "take it easy" is very correct. Not only to protect the engine, but to give the rest of the driveline a chance to get to operating temperature.
The correct oil viscosity is very important as well. Synthetics also help in getting the lubricant where it is needed right away. Low temp flow characteristics of the synthetics is much better than regular oils.

sciguyjim

I think it was in a book called Drive it Forever by Robert Sikorski (?) where he says that it's safe to drive the car as soon as the oil gets circulating, then don't exceed 40 mph for the first 2 miles. This is what I've been doing for the last 13 years.