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I have both car and motorbike. Just common car and motorbike. My car is Toyota 2005, and my motorbike is Honda 2016, I bough both brand new. Both them are fuel injection. Before them, I owned car and motorbike, but both them were carburetor. With those old automotive, I have to warm the engine up until they reach their stationary. The requirement time will be around 5-10 minutes, depend on the weather and time. Morning in rainy season will be different to day time in dry season, however.

With my new automotive that are fuel injection, my habits still there, I still need to take that time to warm up the engine. But I read in many occasions in automotive news said that for fuel injection just required half and maximum one minute to warm up. For my car, since I start the engine up, it will go to around 1,300 RPM, and required around 7 minutes to become stationary, around 700 RPM. The stationary's RPM is clearly stated at the engine cap, with a yellow poster posted there. For the motorbike, I have no idea as no stationary indicator. But another car, Honda, I saw that it takes shorter time, and one Mazda car I saw just required around half to one minute to warm up, as said in the automotive news.

In my understanding, warm up is intended to warm the engine up slowly to avoid the engine's temperature changes so quickly that of course is not good for the engine itself. So my question is, how that warming the engine could be so different? And what is actually that warming up intended? Several time I tested my car without proper warming up, the result is very bad, something like knocking in the engine.

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The specific issue with carburettors are that they are purely mechanical devices and can't directly measure the mass flow rate of fuel they are delivering and as such are quite sensitive to temperature.

Carburettor engines often have a 'choke', either automatic or manual which overrides the normal operation of the carburettor, causing the engine to run rich. This improves starting and warm up but isn't good under load so you need to wait untill the choke turns itself off before you use the engine hard.

With fuel injection the ecu has direct control over the air/fuel mix and can adjust it on the fly according to conditions so all the warm up need to do is get the oil warm enough to work and it doesn't need to worry about getting the flue system in thermal equilibrium as it can adjust air fuel ratio directly as required.

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  • $\begingroup$ Thank you @chris-john. Very nice explanation. I now sure that I can run my car immediately after I started up. $\endgroup$ – AirCraft Lover Nov 16 '18 at 2:07
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Warming up an engine means making sure that the oil and water temperatures reach specified values before significant load is applied.

There are examples of engines that deliver full power from cold : emergency generators for example, but those engines are designed for that application.

There are engines that need to be warmed up properly before use such as engines used in racing.

Car and bike engines are designed to provide power as soon as started, however most specify that gentle use is observed until it is up to temperature - gentle use for 10 minutes is better than 30 minutes sitting at idle...

In the case of the Mazda that you mention there are several possibilities, one is that the ecu is deciding the temperature that you see which has little relevance to the actual temperature of the cooling fluid or oil. This can be checked, if you wish, by fitting temperature sensors and getting the true temperature of the fluids at specific points.

Many cars and other motorized vehicles will have an initial high warm-up rpm for a while, this is usually now decided by the ecu and will be controlled for a smooth idle. My car, will idle at 1100 or so rpm for a minute or so when the outside temperature is -8 or -10 degrees C, then descending to its normal idle speed as the ecu decides.

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  • $\begingroup$ As you said in the first line, "Warming up an engine means making sure that the oil and water teperatures reach specified values before significant load is applied." So, how could a car can warm the engine (oil and water) not more than 1 minute like what Mazda car does? $\endgroup$ – AirCraft Lover Nov 15 '18 at 7:02
  • $\begingroup$ That is not part of the question that you state starting with “my question is..” in your final paragraph. $\endgroup$ – Solar Mike Nov 15 '18 at 7:04
  • $\begingroup$ Yes, your explanation explained my question ""what is actually that warming up intended? But that explanation also left new question, that is how could a car can warm the engine (oil and water) up not more than 1 minute like what Mazda car does? Sorry, not to debate you, I just want the science-based explanation. $\endgroup$ – AirCraft Lover Nov 15 '18 at 7:08
  • $\begingroup$ See my edit, a computer decides what is shown on the dash... not always the "real" temperature... $\endgroup$ – Solar Mike Nov 15 '18 at 7:10
  • $\begingroup$ So my last question, is that quite save to the material composing the engine without proper warm up? Or it just something "we" have to tolerate with the quick time in return? $\endgroup$ – AirCraft Lover Nov 15 '18 at 7:19

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