Many people feel that it’s important to warm a vehicle up before driving off. This has long been the dominant school of thought, dating from when cars had carburetors and many would not run cleanly or respond properly until they reached the correct operating temperature. There was also a belief among owners of cars with aluminum engines that suggested the metal be warmed up before normal driving because of the different coefficient of expansion between steel and aluminum components.
No need to warm up
The truth is that nowadays there is no need whatsoever to warm your car’s engine before driving off. A few seconds of running is enough to get full oil pressure throughout the engine, so you can simply drive off as you would on a summer's day. This has been made possible largely through the global adoption of electronic fuel injection systems, which are calibrated to provide a perfectly combustible mixture at all temperatures, and to provide normal throttle response at all times.
It's OK to drive away
In fact, there’s a strong argument in favor of driving off immediately, and you will find that advice in most car owners’ manuals these days. You see, an engine requires very little fuel to maintain an idle speed, which means there is not much heat being generated. Without much heat, metal in the engine does not expand quickly, and the engine takes longer to achieve its design tolerances—the optimal space between moving parts. As a result, the cold engine experiences a high level of unburned fuel mixture “blow-by,” where gases blow past the piston rings and down into the oil sump, where they dilute the lubricant.
Driving away puts the engine under load, and much more fuel is needed to propel what is, after all, a pretty heavy machine. With more fuel burned in a shorter time, the engine’s components heat up faster, expand quickly, and reach their design tolerance—all of which cuts cylinder blow by to a fraction. Of course, we would not advise full-throttle, high-RPM use on a cold engine, nor would we condone lugging it. But that’s just common sense.
The only reasons we can think of why you’d want to warm your car up for some time before driving would be in icy climates, where you might want heat inside the car along with warm defrosting air to clear windshields for sufficient and safe visibility. In that situation, the additional use of fuel and risk of lubricant contamination may be worth it. Other than that, you can stop wasting fuel and time and simply get on your way.
This article originally appeared on YourMechanic.com as The Importance of Warming Your Car Before Driving.
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