You Shouldn’t Warm Up Your Car On Cold Mornings: Another Reader Weighs In

We’ve heard from more readers about the ongoing debate of whether you should or should not warm up your car and let it idle on cold mornings. With Arctic cold moving into many areas of the country, the question isn’t just academic.

And it’s not just practical, either, though we did hear from a police officer, who offered this: “Two words: auto theft. Then we have to respond to the location of incident, professionally scold the owner, issue a citation, then write a report.”

John Zupanc, a reader from Hamtramck, Michigan, said the author of this letter to the editor — Here’s Why You Should Warm Up Your Car on Cold Mornings — who was wrong when he wrote:

“In the real world of engines and cars, the engine oil needs to get up into the engine and circulate among the valves and many other metal parts to prevent metal to metal contact and minimize wear.

“This can’t happen unless the engine is warmed and oil ultimately reaches operating temperature. When the water is not warmed and engine oil cold and not able to circulate until it gets warm, then the engine is actually subject to unnoticeable internal damage and will not go for the long term if that’s your goal.”

Zupanc writes:

The above is highly misleading if not outright false. All cars use multi-grade engine oils. One of the most common multi-grade combinations is 10W-30. I am sure that most people have heard of it.

What that means is the oil has a range of viscosities ranging from 10 when the engine is cold to 30 when the engine is hot. Thus when the oil is cold and has a low viscosity it flows just as easily as when the oil is hot and has a higher viscosity. Accordingly the oil circulates just as easily at low temperatures as it doses at higher temperatures. Moreover, all car engines use positive displacement oil pumps thus guaranteeing a constant flow rate for a given engine speed.

The only disadvantage to not warming up your engine before driving it is that the piston rings may not seal quite as well, but well enough as they do once the engine is warm. This may in turn somewhat increase blow by for a short period of time.

Premium Fuel vs. Regular Fuel

The only difference between the two fuels is that premium fuel has an additive which decreases the propensity for the fuel to self ignite. Nothing else. Premium fuel is only required for use in high performance engines.

High performance engine may have any or all of the following

• High compression ratio
• Greater advanced spark timing.
• Turbochargers

Any of the above results in higher air-fuel charge pressures in the cylinder which ultimately results in heating the fuel-air charge to a temperature sufficient for self ignition. Hence the charge will ignite before it is required, causing decreased performance, spark knock and may damage the engine. The spark plug should be the only source of ignition and it ignites the fuel at a very precise crankshaft position. Premium fuels only begin burning when ignited by the spark plug. Regular fuel will self ignite in a high performance engine.

Non-high performance engines run at lower cylinder pressures, hence they do not heat up the charge to a temperature sufficient for self ignition. Thus there is no need or advantage for using premium fuel in a non-high performance engine. As a matter of fact, some premium fuels have a lower specific energy content which results in lower engine performance and decreased fuel economy when used in a non-high performance engine. The only time that a midgrade or premium fuel should be used for regular engines is in the case for an older engine that may have hotspots in the combustion chamber caused by carbon build-up that results in spark knock.

The bottom line is this, warming up the engine before driving the car is a waste of time, money and unnecessarily produces more greenhouse gasses. Using premium fuel for a car that does not have a high performance engine is a total waste of money. I have seen a price differential of as much as $0.40/gallon between the two fuels. Additionally, I am sure that the additional processing required to make premium fuel alone uses extra energy and produces greenhouse gasses. So using premium fuel when it is not required is also not the green thing to do.

Photo by Isaac Wedin via Flickr Commons