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My 2013 Honda Fit has been for the past few weeks or so invariably showing me the cold engine light (a blue thermometer with the letter C) when I start it up before or after work (or most other times). I looked in the manual to see what exactly this means, but all it says is something like "the engine is cold" without any more information as to what I should do about it. It turns itself off after a couple minutes of driving.

I presume this information is relevant to something, or else they wouldn't have bothered to make a light for it, but I haven't been able to figure out what.

Garrett Albright
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4 Answers4

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Engines run safely and effectively in a temperature range which is actually fairly narrow. The temperature gauge (or cold and hot indicator lights) typically measure the temperature of the engine coolant itself.

When the car is first started, the engine is cold, and oil will need time to heat up and achieve good flow for lubrication. Until that temperature is reached, the engine is more susceptible to damage at high revs or under load.

Guidance is to drive relatively gently until the low temp light goes out. In a highly tuned car, with tighter tolerances, this is even more important. So treat it as a gentle warning.

If it comes on again while driving, this usually means there is a major problem with your coolant - typically that it has leaked out of the engine entirely so the sensor doesn't read anything! What happens next is that the engine rapidly overheats, destroying the cylinder head gasket, and soon after - the engine itself!

Rory Alsop
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  • Most cars I have dealt with, the temperature gauge reads the coolant temp, not oil... – Nick C Nov 15 '13 at 10:51
  • Nick - d'oh - yes...corrected. – Rory Alsop Nov 15 '13 at 12:06
  • Okay, that sounds good to me. Thanks. The Fit doesn't have much power, so it's possible to a certain extent to "rev the engine" just getting it to match the speed of traffic down Main Street. (Relatedly, I once had an officer almost give me a ticket for "exhibition of speed" for doing just that several years ago - in a '97 Geo Metro/Suzuki Swift. It almost would have been fun to take that to court.) I'll be sure to take more care in the future, though. – Garrett Albright Nov 15 '13 at 19:47
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Checking several Fit forums it means the engine is cold. What this means for you is that the engine has not reached operating temperature so drive it responsibly, no jack rabbit starts, no high revs, no high loads etc. I would assume the light would stay on in event of a defective thermostat or stuck fan relay, essentially over cooling the engine According to some complaints on the forums there is no temperature gauge in some models just a cold light that goes out shortly after start up and a high temp light you hope only lights up on initial start up.

mikes
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Every infernal combustion engine runs best within a stated temperature range. There is a temperature below which the engine is cold, with the heater not working and the need to subject it only to gentle acceleration. There is a temperature at or above which the engine is overheating so badly that it must be shut down and the problem traced and corrected. In between, the engine is warm enough to be driven normally and not too hot to be driven at all, and there is an ideal temperature that the actual engine temperature should be at or close to, that is generally between 3/7 and 5/7 of the way up from too cold to too hot. For monitoring engine temperature with regard to knowing how hot it is, and how the cooling system is working some cars have a temperature gauge that show how hot the engine is in the range from too cold to too hot. Others have signal lights for cold and hot that indicate whether the engine is too cold, too hot, or somewhere in between. And some just have a hot signal.

Sheila Trachtenberg
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I would actually say that contrary to the other answers, you don't need to be concerned at all about the light.

The reasons are two-fold:

  • Firstly, a modern car with electronic throttle control system will be able to limit the throttle opening whenever the electronics of the car suspect that oil has not reached its operating temperature. Thus, your car may already be protecting itself automatically from misuse when the engine is cold.
  • Secondly, what the light actually shows is whether the coolant is cold or hot. It does not show the most important thing for engine wear, the oil temperature. Since oil takes about twice as long to reach operating temperature than the coolant, you can't haul ass immediately after the the light is off.

If I was a car manufacturer, I would use the coolant temperature sensor and some advanced mathematics to develop a model for the most interesting thing, oil temperature. I would also limit throttle opening if the oil has not according to the mathematical model reached the operating temperature. I think the car manufacturers are probably already doing this.

juhist
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  • The car manufacturers are generally not doing this. And my guess would be that it would not go well for them if they did do that - both in terms of reputation and liability. – Rory Alsop Dec 14 '21 at 19:30
  • My car (Toyota RAV4 hybrid) certainly does that, although the limit is not a hard limit but rather a soft limit. If you try to accelerate too hard with a cold engine, you see that pressing the throttle has almost no effect past a certain point. However, if you press it enough, then it at some point decides "the driver really wants to accelerate so let's accelerate even though it causes fast engine wear", and the throttle suddenly starts to have an effect after all. – juhist Dec 14 '21 at 20:18