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Summary
  • Heat shields insulate crucial components from heat emanating from the manifold and exhaust.
  • Common materials used for heat shields are aluminum, basalt, fiberglass, fiberglass yarn, stainless steel, and silica.
  • The catalytic converter, diesel injector nozzles, exhaust manifold, and starter motor usually feature heat shields.
  • Factory-issue heat shields usually last as long as your vehicle but can wear out and fail earlier. You can expect to spend around $150 to $300 on a heat shield repair or replacement.
  • You might have a bad heat shield if you notice a burning smell or rattling noise. Avoid driving with a damaged heat shield because it can cause problems.

Cars have all manner of shields on the body and on the engine that serve different purposes. That plastic hood over the throttle linkage on cars with throttle bodies is there to keep snow from fouling the throttle open.

The molded plastic shields in the wheel wells prevent road splash from getting into the engine compartment and help prevent salt splash from attacking the inner fenders. The fuzzy fibrous shield on the underside of the hood prevents engine heat from cooking the paint on the top side of the hood.

Catalytic converters have an integral heat shield to prevent grass fires (if possible) and to prevent the carpet from smoking on the inside of the car during times when the catalytic converter is blistering hot (and it usually is).

image of a catalytic converter
This catalytic converter has built-in heat shields welded to the converter itself. | Image Source: Richard McCuistian

What Are Heat Shields on a Car?

Because of different factors like engine issues to too much sun exposure, the engine can overheat to the point of damaging the parts around it. Heat shields help prevent that by insulating the car’s crucial components from manifold and exhaust heat.

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Heat tends to radiate from the exhaust, since heat is what travels. Cold is nothing more than the absence of heat. Exhaust heat is many times hotter than the heat produced by the radiator and cooling system and heat shields are typically used to prevent heat damage to nearby components.

Heat tends to radiate from the exhaust, since heat is what travels. Cold is nothing more than the absence of heat.

– Richard McCuistian, ASE Certified Master Automobile Technician

One of the more common heat shields is the plastic shell placed over the 12-volt battery to provide insulation against engine heat that can boil the battery fluid, which causes leakage and corrosion of the battery terminals and the battery tray.

What Are Heat Shields Made Of?

The materials used to create shields vary depending on the application. Generally, heat shields are made of fiberglass, fiberglass yarn, aluminum, stainless steel, basalt, or silica.

Metallic vs. Non-Metallic

Heat shields for cars have two categories in terms of material: metallic and non-metallic.

Metallic heat shields are usually made of stainless steel, aluminum, and other alloys. They are ideal for areas like the fuel and exhaust system.  Most experts recommend aluminum heat shields because of the material’s high thermal conductivity and low emissivity rate. That means aluminum can regulate heat effectively and emit low levels of radiant thermal energy.

Meanwhile, non-metallic materials are usually made of ceramic and nylon. Heat shields with thermal ceramic coating, in particular, are often recommended for high-performance vehicles to improve insulation.

Heat Shield Applications

Heat shields on cars can protect different parts of your engine. Here are some crucial components that use heat shields:

Starter Motor

Some starter motors have heat shields to protect the copper wiring inside them. The conductors in the starter motor are vulnerable to heat damage, and a heat shield helps insulate it from devastating engine heat.

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Catalytic Converter

The engine’s catalytic converter won’t work if it doesn’t reach a certain temperature range, usually between 900°F and 1,600°F, during operation.

Unfortunately, extreme heat can damage nearby components. That’s why many cars have heat shields around their catalytic converter to protect nearby components like the chassis and even the passenger compartment.

Diesel Injector Nozzles

Diesel injector nozzles are spring-loaded closed valves that deliver fuel into the combustion chamber. These nozzles can heat up, so their outer shell has a heat shield. The outer shell of a diesel injector nozzle can also have external threads where the cylinder heads are sealed.

Exhaust Manifold

An exhaust manifold gathers hot gasses and sends them to the exhaust pipe. The gasses move through the catalytic converter, muffler, resonator, and tailpipe where they are released into the atmosphere.

The exhaust manifold usually gets extremely hot during engine operation, so it usually comes equipped with heat shields to protect nearby spark plug wires. Keeping the heat in the exhaust manifold also improves exhaust emissions.

How Long Do Car Heat Shields Last?

Your factory heat shields should last the life of your vehicle. However, certain factors like vibration, rust, and debris can take their toll on engine heat shields—especially those that are in vulnerable places.

Signs of a Bad Car Heat Shield

Keep an eye out for these symptoms that tell when your car’s heat shield is starting to fail:

Burning Smell

When extreme heat damages engine parts, it usually warps or burns them, creating a noticeable burning odor. You might also notice that the hood is too hot to touch.

Rattling Noise

mechanic checks for heat shield rattling noise
If you’re hearing rattling noises and your car frequently overheats, don’t waste time and take your ride to an auto repair shop right away.

If you’re hearing rattling noises and your car frequently overheats, don’t waste time and take your ride to an auto repair shop right away. The sounds might be coming from loose heat shields.

If rust isn’t the culprit, the mechanic would simply tighten up the heat shield to resolve the issue. However, if your heat shields came loose because their welded sheet metal part is rusty, you might need to get heat shield replacements.

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How Much Does a Car Heat Shield Replacement Cost?

You can expect to spend around $150 to $300 on a heat shield repair or replacement. This ballpark estimate includes labor costs.

Take note, however, that the price can significantly vary depending on your car’s make and model, the specific heat shield that needs to be replaced or fixed, and the labor rates in your area. You must also consider taxes and other related repairs.

Can I Drive With a Damaged Heat Shield?

Although it’s technically possible to drive your car with a damaged heat shield, it’s highly recommended that you don’t.

Heat shields are on different components for a reason. Let’s take the catalytic converter as an example. Did you know that vehicles can start a fire all because of a hot catalytic converter? The intense heat can cause dried leaves or tall grass underneath the car to ignite.

Moreover, engine overheating can damage various parts, like your seals and gaskets, and create cracks in your engine blocks. You can read our article on the effects of engine overheating to learn more.

Each safety component on your vehicle is there for a purpose. Taking good care of these components and replacing them when needed will help keep your trips safe and hassle-free. Plus, it will help you make the most out of your car’s service life. So make sure your car heat shields are always in great shape.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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