“Engines and Humans need exhaust Systems.”

To understand how hot the exhaust manifold gets, let’s consider the functionality of the exhaust system and the exhaust manifold temperature.

 

Exhaust manifold – How does it work?

• The engine’s exhaust valve, situated at the end of the exhaust stroke, sends the high-pressure and high-temperature exhaust gases, as well as the sound waves produced, to the exhaust manifold.

• Heat from the exhaust manifold reaches the oxygen sensor, which is fixed at the entrance of the pipe connecting the exhaust manifold and catalytic converter.

• The oxygen sensor consists of a zirconium dioxide sensing element. When the exhaust gas containing oxygen passes through the sensor, the sensor produces voltage signals according to the oxygen level. These signals are sent to the Engine Control Unit (ECU). With the signals, the ECU decides the required air and fuel ratio for the next stroke of the engine.

• Exhaust gases and sound waves go into the catalytic converter. Exhaust gases include harmful gases like carbon monoxide, hydrocarbons, and nitrogen oxides. A catalytic converter has two ceramic chambers with platinum and rhodium in one chamber and platinum and palladium in the other. These are the catalysts. As harmful gases enter the first chamber, it gets heated. So, the catalyst starts to react with the gases. The catalyst converts the oxides of nitrogen into oxygen and nitrogen. These gases then enter the second chamber, where the carbon monoxide reacts with the oxygen to form carbon dioxide. The residual hydrocarbons react with oxygen and produce water and carbon dioxide.

• Another oxygen sensor is located at the exit of the catalytic converter pipe. It checks the catalytic converter’s proper functioning.

• Through this process, harmful gases have been converted into less harmful gases like nitrogen, carbon dioxide, etc., but they still contain sound waves produced by the engine.

• Gases are passed into the muffler to avoid sound. Mufflers have different chambers. The first chamber has holes in it. When sound waves pass through the holes, they get hit by the walls of the chamber, where friction is created, thereby reducing the sound waves. The sound waves are almost nullified as they pass through all the muffler chambers and the resonator.

• The exhaust system’s last unit, the tailpipe, expels the less harmful gases and the low sound waves.

“The higher the heat, the more the exhaust.”

 

How hot does an exhaust manifold get?

The exhaust manifold gets a higher temperature because it is the part that gets the hot gases coming out of the engine. When the engine runs for an extended period, the temperature can rise to 1200 °F or even 1600 °F. Cast iron exhaust manifolds are tolerant of such high temperatures.

When there is a hindrance in the hot gas flow, like a curve or bend near the engine or 4-cylinder exhaust manifold, it gives more reason for a very hot temperature. Once the engine ignition is on, the exhaust manifold gets heated as the engine has started functioning.

 

Why is the Exhaust Manifold glowing red?

The heat is transferred to the catalytic converter. As we saw earlier, the catalytic converter undergoes some chemical reactions, which release heat energy. Moreover, any fuel left without complete combustion may be burned during oxidation in the catalytic converter, which can also increase the temperature.

Under normal conditions, catalytic converters can reach temperatures of up to 1000 °F. If the unburnt fuel is burned, the temperature of the catalytic converter may even reach 2000 °F. So, catalytic converters have the highest temperature.

When a diesel engine is running normally, the temperature of the diesel exhaust manifold can range between 300 and 500 °F. When the RPM increases, the temperature also increases. When the engine is functioning, the temperature will be high rather than at an idle condition.

When the exhaust manifold reaches a high temperature, it starts to glow red. It is common for both petrol and diesel engines to have such a red hot exhaust manifold that functions with turbochargers. A motorcycle exhaust, though it has a small engine, will also get a higher temperature of up to 1600 °F.

 

Exhaust manifold temperature in degrees Celsius

The muffler, despite its proximity to the tailpipe, can reach temperatures of up to 1200 °F when the engine runs at high speed. The exhaust manifold temperature ranges from 100 to 900 °C in degrees Celsius.

When the vehicle is turned off, the exhaust manifold and tailpipe temperature will cool down to 10 – 100°  within a few minutes. However, the catalytic converter may remain hot for at least an hour or two.

 

Factors determining the exhaust system temperature:

The speed, or throttle or RPM, is the main factor that decides the temperature of the exhaust system. The higher the combustion of fuel, the higher the temperature will be.

The length of the pipes connecting the various parts of the exhaust system and the length of the tailpipe determine the temperature to some extent. If the pipe is lengthy, most of the heat is lost even before it reaches the outlet. If the pipe were not so lengthy, then comparatively, the gas emitted by the exhaust system would be of a higher temperature.

The functionality of the engine is also a deciding factor. When the engine utilizes the correct amount of fuel and produces the optimum amount of energy, the corresponding increase in temperature will be seen in the exhaust system. A faulty engine may sometimes cause more heat in the exhaust system.

 

How to maintain the Exhaust System temperature?

Proper insulation with high-temperature exhaust paint on the pipes can prevent heat from the exhaust system from radiating to other parts. Radiation shields are nowadays used to eliminate radiation problems. Unusual higher or lower temperatures in the exhaust system indicate a malfunctioning system and must be addressed.

 

Conclusion:

An average exhaust manifold temperature would work at 400°F to 600°F and may extend up to 1200°F.