We get a lot questions about overheating and if the shield causes any overheating of the converter. Here is the technical answer from our engineering department with over 30 years experience in catalytic converters and exhaust systems.
Bottomline, the shield does not cause excessive heat to the converter. Excessive heat in a catalytic converters is cause by improper air/fuel ratio, misfires, a bad egr, and excessive engine load. A shield is does very little to increase in heat in and around the converter. We have even seen in some of our tests that our shield lowered exhaust temperatures in parts of the exhaust tunnel which the shield covers.
*Even in areas with triple digit temperatures, the air temperature will not impact the converter with our shield. Your catalytic converter operates from 400-1000+ degrees, therefore even areas of 100+ temperatures will still be much cooler than the operating temperature of your converter. Heat from your vehicle will still want to escape and not the other way around.
How or why do you ask? It has to do with the aerodynamics and how the air traveling over the exhaust tunnel becomes very turbulent and creates pockets of stagnant air in the exhaust tunnel. The catalytic converter's radiant heat gets trapped in the pockets of stagnant air and won’t dissipate through the exhaust tunnel. With our shield the air underneath the vehicle becomes has more laminar flow (smoother air flow) and reduces the stagnant air pockets. When air travels over our shield and louvers vents, the air increases in velocity which causes a negative pressure (vacuum pressure) and extracts the heat out of the exhaust tunnel.
We specifically use louvers and design our shields to address stagnant air (no other companies do this) and reduce excessive heat. Be careful of any design that does not consider proper heat extraction. There are some designs out there that encapsulate the catalytic converter, which is dangerous and poorly thought out (check out our blog on this here). With those designs, the heat has nowhere to go but up and can burn the insulation and carpet. Other designs just cut out slits/holes that do not efficiently extract heat and can actually give thieves a head start if they wanted to cut through the shield. The details matter and here at MillerCAT we go through a thorough design and production process to give our customers the confidence that they are buying the best products for their vehicles.
Additional questions and answers
Will the shield cause a fire?
No, the shield will never get hot enough to cause a fire even if you park in tall dry grass. Even after driving your vehicle, the shield can almost be safely touched (something we don't recommend but which we tried for your benefit).
Will the shield overheat my converter?
No, a catalytic converter operates at a much higher temperature than the area surrounding it and does not need to be cooled. A converter must be heated in order to work efficiently and must retain this heat throughout operation. This is why converter substrates are wrapped in thermal matting and sometimes come with heat shields. Manufacturers learned that heat helps converter efficiency and started placing converters closer to the engine to heat the converter faster. Most older vehicles have underbody converters (that are completely exposed) while newer vehicles will be nearer to the exhaust manifold of the vehicle.
The main concern about a shield and temperature is when a shield prevents heat from dissipating around a converter and traps it. Most designs won't have this problem unless it boxes in the converter. When this happens, the air temperature around the converter rises significantly and can heat up the bottom floorboard and risk causing damage.