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Should I drive gently when my engine is cool?

Our neighbor’s 63 Chevy had a yellow “cold” light. When she’d give me a ride to school in the winter, it’d take maybe 4-5 blocks for it to go out. I think that would correspond to getting to the first notch of the temp guage.

Cavell writes that “well, our new honda has a blue dash light to inform you the motor is cold”. I’m guessing the light to which Cavell refers is like the “Low Engine Coolant Temperature Indicator Light” on my 2013 Mazda 2. This light (a picture of a thermometer, sort of; I don’t know how to post an image) according the Owner’s Manual “…illuminates continuously…” (in blue) “…when the engine coolant temperature is low and turns off after the engine is warm”.
Could someone explain for those of us who are not mechanically-inclined whether the light staying illuminated means that the “motor is cold”?
It is frequently below 20 degrees when I start my car around 8 am in Boston. However, I do not let the car idle for more than a few seconds before starting to drive, though it takes me at least six minutes to get to the interstate. If I recall correctly, a few weeks ago it was about 12 degrees and the blue light remained illuminated for about eight minutes. I don’t recall any problem with operating the car, however.

@Jazzhands Our Mazda also has a “cold engine” indicator light. Our Toyota has a temperature gage in stead.

The Mazda blue light only tells you that the engine has not warmed up sufficiently to use the heater. It’s not a failure indicator light. If the car overheated, it would turn RED; that’s the time to immediately stop the car and call the AAA.

This is all explained in the OWNER’S MANUAL.

Read the Owners manual- Now there is a novel thought.

@VolvoV70 Yes!! The owner’s Manual is the world’s most unread bestseller!! As they say, when all else fails, read the instructions!

As I used to put it RTFM ! (Read The F… Manual)

I have a Mazda AND I read the manual. The blue light means the engine is cold so you can’t get any heat AND you should drive gently. The red temperature light means the engine is overheating. The red light will FLASH when the overheating is serious. I prefer a temperature gauge but I imagine that the lights are more appropriate based on the automotive IQ of most drivers today.

My preference, and the way my dad taught me is the following.

Above freezing, Let the engine idle for 30 seconds to a minute.
This is normally when I realize that I forgot my cel phone or wallet anyway!!!

Below freezing, I let it idle at least 3-5 minutes before putting it in drive. By the time I am to the major road the engine is plenty warm enough to go on.

Below 10 degrees, I let the truck idle for 5-10 minutes before putting it in drive. I’m getting to haste the cold the older I get and I enjoy the fan blowing at least half warm air on me.

I’m waiting for a V6 that, one cylinder keeps running to keep the engine warm over night while you sleep.

I know we don’t really need to warm our engines this much and no harm would be done if I just hopped in and drove.
It is just my preference!!!


Joe Guy: My 2010 Kia Forte manual is quite thorough. My new cell phone had no manual. The only instruction I could find was charge battery. It was noted that the manual is on the phone. OK… Of course the battery was not installed and I could see no obvious way to open the phone. It took quite a bit of searching online to find instructions for opening the phone. There were two steps involved and they were not intuitive!

I’ve never had a car with a blue “cold engine” light, but I like the idea. I much prefer a temp gage (which my car has), but a lot of people have difficulty interpreting gages.

My father’s '66 Ford Galaxie 500 had a blue “cold engine” light in addition to a red “overheated engine” light, so the concept is certainly not a new one. And, in fact, I never again had that feature until I bought my 2011 Outback.

While I do prefer a temperature gauge, that blue light (with a pictogram of a thermometer) is a good reminder to keep engine RPMs low until that light extinguishes itself. I make it a rule to keep RPMS to no more than a little over 2k until that blue light disappears.

I’ve always wondered why car manufacturers don’t combine gages with warning lights. It seems to be “either/or” on every car I’m familiar with. Gages are great, but they don’t warn you like lights do, and lights are great but you don’t know something’s happening until it’s happened.

Each of my post 1990 vehicles have both gauges and warning lights.

I have to push a button several times to bring up the temperature display. The only times I idle for more than about 30 seconds is to clear condensation/rain from the mirrors/rear window which takes about 2 minutes or clear frost/ice which only takes 2 to 8 minutes. We had a brief ice storm in late December. One morning with a thin glaze that took the 8 minutes and the next morning with 1/4 inch plus when I didn’t have to go anywhere.


I’ve also seen plenty of vehicles with gauges and warning lights

In most cases the warning light was in the same “pod” as the gauge

What I personally dislike are those cars that don’t even have a coolant temperature gauge. My brother’s Mazda is one of those

While I don’t consider Benz to be a particularly reliable brand, they did do something rather innovative several years back . . . while the vehicle(s) didn’t have a “physical” coolant temperature gauge with a needle . . . the feature was incorporated into the multifunction display. When selecting it . . . and it was actually not hard to do . . . I seem to recall it looked like a sort of thermometer, with the actual temperature displayed in numbers.

My brother’s Mazda does not even have that. Everything is fine, until the coolant temperature “idiot” light illuminates

Sgtrock, the sequential button setup requiring pushing a button multiple times to find what you want while watching an LCD display is becoming more and more common, and it’s a pet peeve of mine. It requires the driver to take his/her focus off of driving while scrolling through the menus. The guys that design these things seem to consider it high-tech, but I’ll take the old fashioned controls any day. On my cars years ago I could change my heating duct configuration, change the temp setting, change my radio station or volume, and do just about everything I wanted without ever taking my eyes off the road. Can’t do that in my current car.

Aircraft have (or used to have… I haven’t been in a cockpit in years) all the switches and knobs intentionally designed in entirely different sizes and shapes, so that a pilot could know by feel what he/she was grabbing, and where relevant where it was set. It made for some weird shaped knobs, but it worked. I’ve always felt that automotive interiors should be designed with the same attention to safety.

Me, my oldest is a 43 year old Ford 4wd truck, owned for 42 years.

For the last 30 years I’ve averaged over 35k/year. If I owned a vehicle 42 years I would have almost 1.5 million miles.

Here’s another point of view in the comments section of the Yahoo article knfenimore posted.
"The key difference is that electronic fuel injection comes with a sensor that feeds the cylinders the right air-fuel mixture to generate a combustion event."
This statement made by the author is simply not true, plain and simple. Fuel injection mixture is controlled through the computer by two main sensors. The coolant temperature sensor and the Oxygen sensor(s). However when a fuel injected engine is cold it runs on a pre-programmed rich fuel map until the coolant temp and O2 sensors warm up enough to come online. Only after these sensors are warm do they control the amount of fuel being injected into the engine

Wow @Don355, it has been my observation that the injector pulse width was determined primarily by throttle opening and manifold pressure (speed density) or Mass Air Flow. Of course I do recall that an open circuit temperature sensor could prevent a cold engine from starting. But if most engines ever get lit the computer can somehow throw in a value for any missing sensor to keep the engine running well enough to limp along. I seem to recall that several early systems would give the bogus data in diagnostic data link and confuse diagnosis to those unaware of the situation.

Don, the comment you referred to is simply, as you said, not at all accurate. The concept of the statement is, however, somewhat accurate. In both carbureted and fuel injected engines the idea is to feed the best amount of fuel into the engine’s induction system to try to achieve the best operation based upon the technology feeding the fuel in.

Carbs used fuel being drawn from a little bowl of fuel, the amount in the bowl being controlled by a float attached to a needle valve, by the lower-than-ambient pressure that was felt against the venturi wall (lateral wall pressure) by virtue of the air being drawn into the engine by the pistons. The more air that got drawn in, the lower “lateral wall pressure”, and the more fuel that got drawn in, since the pressure in the bowl was kept constant. It was essentially a system that metered fuel by a low (by fuel injection standards) differential in pressures. Compensation for temperature variation was accomplished by a bimetallic spring that opens and closes the throttle plate, and a “high idle cam” driven by the spring that mechanically opens and closes the throttle at idle. Throttle response to the pedal was via a mechanical cable, and the aforementioned “lateral wall pressure” simply was a result of the throttle opening changing. The changes in that pressure simply drew more fuel in from the float bowl or not.

Fuel injection simply uses sensors to replace all that mechanical and pressure-differential controlled stuff. And it uses much higher fuel feed pressures, usually 40psi or above, to get much finer sprays.

With EFI, the computer takes a number of sensor inputs to determine the appropriate inputs, including the throttle position sensor, the crank or cam speed sensor, the manifold absolute pressure sensor and/or mass airflow sensor, the temp sensor, and the upstream oxygen sensor. These are sometimes collectively referred to as “engine demand signals”. If the temp sensor sends a signal to the ECU indicating that the engine is cold, the algorithm program simply assigns a preprogrammed substitute oxygen sensor number to the equation that runs the pulsewidth longer than it would be for a warm engine given all the same other readings.

The ECU is also programmed to ignore the downstream oxygen sensor reading, as it would otherwise tend to trip a Check Engine Light every time the engine is cold. The catalyst in the converter doesn’t begin to do its thing until the platinum palladium reaches about 400F.

And it also bumps the idle up… in modern engines the throttle plate is controlled by a motor driven by the ECU rather than a cable attached to the pedal.

I don’t know that the computer is programmed to substitute any readings other than the oxygen sensor, but with systems that go into “limp” mode, others that shut off individual cylinders, and all the other stuff engines can do now, it would not surprise me if they could. With a computer program, anything is possible… and for the techies, I suspect automotive engine computers aren’t even a challenge. With the sensor output signals defined, the engine demands (how much fuel will the engine need under the specific engine conditions as defined by the sensor signals), and the injector specs, the programming itself is, I suspect, a “piece of cake”.

Pant-pant, I hope I didn’t get carried away. Somebody fact-check my work for me. Please.