How Hot Does A Car Exhaust Get?

Опубликовано 12 апреля 2017, 14:00

How Hot Does Your Car Exhaust Get?
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In this video we are discussing exhausts, and particularly we’re checking out the exhaust of my Honda S2000 after a cold start. Once the engine turns on, you can see the exhaust manifold immediately heats up, represented by point number two which is just before entering the catalytic converter. A short duration passes where it seems like the catalytic converter takes in all of the exhaust heat, and then the piping exiting the cat begins to quickly heat, represented by point number 3. Point number 1 is the heat shield surrounding the converter, which in hindsight should have been removed, however you can still see the cat through the cracks, and as you’ll see later on in the video, the secondary oxygen sensor becomes one of the hottest points on screen.

Catalytic converters are used to turn nitrogen oxides, carbon monoxide, and hydrocarbons into less harmful gases. The idea is that for the various molecules that enter the cat, upon exit you simply have nitrogen, oxygen, carbon dioxide, and water. For the exact details, see my video on how catalytic converters work, but know that as these chemical reactions occur, they create heat. Additionally, any unburnt fuel will burn in the oxidation stage of the catalytic converters. When your car first starts it tends to run rich to help promote fuel atomization, however by running rich it also causes a burden on the catalytic converter, and can cause it to get very hot.

The converter isn’t effective until it reaches a certain temperature. Below about 400 degrees Celsius, the proper chemical reactions won’t occur. The systems are designed to operate at temperatures as high as 1000 degrees, however at this point the reactions are less efficient, and if the cat starts to get much hotter, it can begin to melt and permanently fail. It’s important to note that the exhaust gas temperatures are hotter than the exhaust pipes we’re viewing.

It is interesting to see how large of a temperature drop occurs upon entering and exiting the cat. After about four minutes of running, there’s well over a 50 degree difference. Looking at the split as the exhaust divides between the two rear mufflers, it’s interesting to see that the heat distribution, and thus the exhaust distribution, does seem quite even, with the right exhaust pipe seeing temperatures just slightly higher than the left.

The mufflers themselves remain moderately cool relative to the rest of the system, certainly helped by the large surface area and cool ambient temperatures. While the exhaust gases exiting still have high temperatures, the very tips of the tailpipes themselves, as you may expect, remain the coolest portion of the exhaust. Now looking back at the exhaust header and cat, you can see the O2 sensor has now become one of the hottest spots, indicating the heat generated by the cat, reaching over 180 degrees Celsius.

What happens as we rev up the engine? The exhaust manifold quickly heats, reaching temperatures of 210 Celsius in less than 30 seconds. Observing the engine, you can see the exhaust and engine heat shield actually does a fantastic job of protecting electrical components from excessive heat.

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