How Hot Does An Exhaust Manifold Get?- Best Guide For 2022

An exhaust manifold is a primary device in the engine exhaust system. It is connected to the engine to collect the emissions that are harmful residuals released when the engine works and generates energy. It passes the emissions to the continuing chambers of the exhaust system that convert the harmful chemicals into eco-friendly ones.

“Engines and Humans need exhaust Systems”

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

 

Exhaust manifold – How does it work?

• The exhaust valve in the engine, which is situated at the end of the exhaust stroke, sends the exhaust gases that are at high pressure and temperatures, as well as the sound waves produced, to the exhaust manifold.

• From the exhaust manifold heat reaches the oxygen sensor, which is fixed at the entrance of the pipe that connects the exhaust manifold and catalytic converter.

• The oxygen sensor consists of a zirconium dioxide sensing element. When the exhaust gas that contains oxygen passes through the sensor, the sensor produces voltage signals as per the oxygen level. These signals are sent to the Engine Control Unit (ECU). With the signals, the ECU would decide 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 oxides of nitrogen. A catalytic converter has two ceramic chambers with platinum and rhodium in one chamber and platinum and palladium in the other chamber. 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. That checks the proper functioning of the catalytic converter.

• 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.

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

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

“The higher the heat, 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 is running 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 flow of the hot gas, like a curve or bend near the engine, 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 Exhaust Manifold glowing red?

The heat is transferred to the catalytic converter. As we saw earlier, the catalytic converter undergoes some chemical reactions, and the chemical reactions release heat energy. Moreover, any amount of fuel that was left without complete combustion may get burnt during oxidation in the catalytic converter and can also increase the temperature.

Catalytic converters can reach temperatures of up to 1000 °F under normal conditions. If the unburnt fuel gets burned, then the temperature of the catalytic converter may even reach a temperature of up to 2000 °F. So the 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 a red color. 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

When the engine is running at high speed, the muffler, despite its proximity to the tailpipe, can reach temperatures of up to 1200 °F. Exhaust manifold temperature in degrees Celsius ranges from 100 to 900 °C.

The exhaust manifold and the exhaust tailpipe temperature will cool down a 10 – 100°  within a few minutes when the vehicle is turned off. But 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. With higher the combustion of fuel, the higher the temperature will be.

The length of the pipes that connect the various parts of the exhaust system and the length of the tailpipe determine the temperature to an extent. If the pipe is lengthy, most of the heat would be 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 of the pipes can prevent the radiation of heat from the exhaust system to other parts. Radiation shields are nowadays used to get rid of radiation problems. Unusual higher or lower temperatures in the exhaust system indicate a malfunctioning of the system and must be taken care of.

 

Conclusion:

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