Automotive Heat Shields and Why Every Car Needs Them

A car heat shield is a barrier between a heat source and something that needs protecting. The heat source is usually the exhaust, the engine block or the turbo. The part being protected might be a fuel line, a wiring loom, the battery, the cabin floor or your feet.

Most shields do two jobs. A reflective face bounces radiant heat back towards the source. An insulating core slows down the heat that still gets through. Get both right and nearby parts run cooler and last longer. Compare every sheet and panel in our car heat shield range.

 

What a heat shield actually does

Heat moves in three ways. Conduction travels through solid contact, like a bracket bolted to a hot manifold. Convection moves with air, like hot air rising off the engine and pooling under the bonnet. Radiation travels as infrared energy straight across an air gap, the way you feel a campfire on your face.

In an engine bay, radiant heat from the exhaust and turbo does most of the damage. That is why most automotive heat shields have a shiny aluminium or gold foil face. The foil reflects radiant heat. The fibreglass or polyester layer behind it slows conduction into the panel or part you are protecting. For the physics, see our guide to conduction, convection and radiated heat.

 

Where the heat shields are on your car

Most cars leave the factory with several. The common positions are:

  • Over the exhaust manifold or headers, bolted to the engine or the manifold itself
  • Around the catalytic converter, often as a clamshell in two halves
  • Along the underside of the floor pan and transmission tunnel, above the exhaust
  • Beside or over the fuel tank
  • On the firewall, between the engine bay and the cabin
  • Under the bonnet, as a pad or liner

If you are chasing a rattle, the exhaust manifold shield and the catalytic converter shield are the two most likely culprits, because they take the most heat cycles.

 

Do you need a heat shield on your car?

For a standard car in normal use, keeping the factory shields in good condition is usually enough. You need extra protection when something changes the heat load. Common triggers:

  • Aftermarket extractors, headers or a bigger exhaust that runs closer to the floor or firewall
  • A turbo conversion or a tune that raises exhaust temperatures
  • Towing, low-range crawling or long idling with little airflow under the vehicle
  • A hot floor or firewall you can feel through your boots
  • Hoses going hard, wiring insulation cracking or a battery failing early
  • A fuel line, fuel filter or second battery relocated closer to the exhaust

 

Where your car needs automotive heat shielding

Firewall

The firewall separates the engine from the cabin. Heat soaking through it makes the footwells and pedals hot. A reflective adhesive shield on the engine side cuts the radiant heat reaching the cabin.

Floor and transmission tunnel

The exhaust and catalytic converter run directly under the floor. On 4WDs and utes this is the most common hot spot. Kool Wrap recommends the 5mm heavy duty shield, with its thicker 0.25mm foil face, for under-car jobs where the exhaust heats the floor. Our guide to fixing a hot floor in a LandCruiser or 4WD walks you through it.

Fuel tank and fuel lines

Fuel tanks and lines near the exhaust pick up heat, and hot fuel can vaporise in the line. A reflective shield on the tank or a sleeve over the line keeps radiant heat off.

Starter motor

Starters often sit beside the exhaust manifold or front pipe, and heat soak leads to slow hot starts. A starter motor heat shield covers the body of the starter.

Battery

Under-bonnet heat speeds up battery wear. A battery insulation kit wraps the battery case. It fits batteries up to 20cm high and up to 1.0m in circumference, and suits lead acid, AGM and lithium.

Intake and airbox

Your engine draws in cooler air when the air around the intake is cooler. A reflective shield on the airbox or intake pipe limits the heat the incoming air picks up.

Bonnet underside

Engine heat rises and bakes the bonnet. Under bonnet insulation comes as 10mm and 12mm foam adhesive pads and a premium compressed felt, fixed to the underside between the bracing.

 

How to fix a rattling heat shield

Factory shields are thin pressed steel or aluminium held on with small bolts, clips or welded tabs. Years of heat cycles, vibration, water and mud corrode the mounting points. The shield then works loose and buzzes against the exhaust.

A loose heat shield usually sounds like a metallic buzz, rattle or tinny vibration that comes and goes with revs. It is often loudest at idle or at one particular engine speed, and it can sound alarmingly like something serious. Most of the time it is a shield that has let go at one corner.

A rattling shield is a warning, not a nuisance to cut off. Fix it instead:

  1. Let the exhaust cool completely before you touch it.
  2. Find the loose shield. Tap along the exhaust with a rubber mallet until you hear the rattle.
  3. Check the mounts. Where the tabs are sound, refit the shield with new bolts or clips.
  4. Where the tabs have rusted through, hold the shield in place with a large stainless steel hose clamp, or have an exhaust shop weld on new tabs.
  5. If the shield itself is rusted out, replace it with a new factory part or a correctly mounted aftermarket shield.

Never remove a factory heat shield and leave it off. It is there because something nearby, often the floor, the fuel tank or a fuel line, needs protecting from exhaust heat.

 

What heat shields are made of

  • Reflective aluminium foil. The most common face, and it shrugs off moisture. The foil on our 1.5mm silver shield has a melting point of 650°C.
  • Gold foil. Gold Reflecta Shield uses a gold-coloured reflective foil laminated to fibreglass. It suits airboxes and tight spots where you want a thin sheet.
  • Fibreglass cores. Fibreglass sits behind the foil as the insulating layer. The fibreglass backing on the 1.5mm silver shield is rated to 593°C.
  • Fibreglass and polyester cores. The 4mm and 5mm Aluma Shield II sheets put an embossed aluminium face over a fibreglass and polyester core. They reflect up to 95% of radiant heat and passed a 30-hour oven test at 246°C with no failure.
  • Embossed multi-layer aluminium. Semi-rigid panels stack layers of embossed aluminium with no adhesive, in single layer at 1.8mm and in two, four and six layer builds up to 3.3mm. They cut radiant heat by up to 90% and are designed for up to 650°C.

 

Flexible adhesive or semi-rigid?

Choose a flexible adhesive shield to cover a panel, such as a firewall, floor pan, tunnel, airbox or fuel tank. You cut it with scissors, peel the liner and stick it on. Our adhesive heat shield installation guide covers prep, cutting and sealing the edges.

Choose an embossed semi-rigid heat shield when the shield needs to stand off a very hot part, or when there is no clean, flat surface to stick to. You fold and form the panel by hand, then mount it with brackets or hose clamps.

Never stick an adhesive shield directly onto an exhaust pipe, manifold or turbo housing. Kool Wrap does not publish a temperature rating for the adhesive, so keep adhesive sheets on the panels and parts near the heat, not on the heat source. To cover the pipe itself, use exhaust heat wrap.

For a part-by-part breakdown, see the best heat shield material for each engine bay part.

 

Car heat shield FAQs

 

What is a heat shield on a car?

It is a barrier between a heat source and something that needs protecting. Most car heat shields have a reflective metal face that bounces radiant heat back towards the source, and an insulating layer behind it that slows the heat that still gets through. Cars carry them over the exhaust, around the catalytic converter, under the floor and near the fuel tank.

 

Where is the heat shield on a car?

Most cars have several. Look over the exhaust manifold, around the catalytic converter, along the underside of the floor pan above the exhaust, beside the fuel tank, on the firewall between the engine and the cabin, and under the bonnet. A rattle usually comes from the manifold shield or the catalytic converter shield.

 

What does a loose heat shield sound like?

A metallic buzz, rattle or tinny vibration that changes with engine speed and often disappears above a certain rev range. It is loudest at idle on many cars. It sounds worse than it is, and it is usually one corner of a shield that has rusted off its mount.

 

Can you drive with a loose heat shield?

You can drive a short distance to get it looked at, but it is not something to leave. A shield that comes fully loose can drag on the road or fall off, and the part it was protecting then sits in direct exhaust heat. Get it refitted or replaced rather than removed.

 

How long can you drive without a heat shield?

There is no safe number of kilometres. Removing a shield leaves whatever it was protecting exposed to exhaust heat, which on the floor pan or near a fuel line is a real risk rather than a theoretical one. Refit it, replace it, or fit a correctly mounted aftermarket shield in its place.

 

Do you need a heat shield to pass inspection?

Requirements vary between states and between inspection types, so check with your inspector or your state authority rather than relying on a general answer. What is consistent is that a shield hanging loose, dragging or missing over the exhaust is the kind of defect an inspector notices.

 

Do you need a heat shield on your exhaust?

If your car came with one, yes. Factory shields sit where the manufacturer found a heat problem. On a modified exhaust, the question is whether the new pipe runs closer to the floor, the fuel tank or the firewall than the old one did. If it does, it needs shielding even if nothing rattles.

 

What are heat shields made of?

Factory shields are thin pressed steel or aluminium. Aftermarket shields use a reflective aluminium or gold foil face over an insulating core of fibreglass, or fibreglass and polyester. Semi-rigid shields are multiple layers of embossed aluminium formed into a panel, with no adhesive backing.

 

Can you make a heat shield out of aluminium foil?

Kitchen foil is not a heat shield. It has no insulating layer, it tears, and it does nothing about conducted heat. What makes a shield work is the reflective face and the insulating core together. If you want a thin sheet for a tight space, the 0.5mm gold shield is the product that does that job properly.

 

Need help choosing?

Compare every sheet thickness and panel style in the Kool Wrap heat shield range. Not sure which shield suits your car? Call 1300 44 33 34 with the make, model and where the heat is coming from. Kool Wrap has supplied heat protection in Australia since 1995.