Exhaust Systems

According to the Exhaust Systems ILM, the primary function of an exhaust system is to:

Increase engine noise for performance applications Safely route combustion gases away from the engine and passenger compartment while controlling noise and backpressure Cool engine coolant Store unburned fuel

The ILM identifies the main exhaust system components as:

Radiator, hoses and thermostat Exhaust manifold(s), pipes, catalytic converters (if equipped), mufflers, resonators and tailpipes Fuel tank, lines and injectors Air filter, ducts and throttle body

Exhaust manifolds are typically made from:

Thin plastic for insulation Cast iron or fabricated steel/stainless steel to withstand high temperature and thermal cycling Glass fibre Aluminum only

A key purpose of the exhaust manifold is to:

Control coolant flow Collect exhaust gases from each cylinder and direct them into the exhaust system Meter fuel into the cylinders Lubricate valve train components

The ILM explains that exhaust system leaks near the engine are dangerous because:

They only increase noise slightly They can allow carbon monoxide and other gases into the passenger compartment They improve fuel economy They increase cooling efficiency

Exhaust flex joints are used primarily to:

Increase exhaust restriction Absorb engine and drivetrain movement to reduce stress on exhaust pipes and manifolds Hold the exhaust rigidly in place Filter exhaust gases

The muffler’s main function is to:

Increase exhaust gas temperature Reduce exhaust noise using expansion chambers and sound-absorbing materials or tuned flow paths Store catalytic material Filter particulates from the coolant

A resonator in an exhaust system is used to:

Replace the muffler Further tune and reduce specific exhaust sound frequencies Hold the oxygen sensor Support the transmission

Exhaust hangers and insulators are important because they:

Increase exhaust gas speed Support the exhaust components and isolate vibration and noise from the body Block exhaust flow Control coolant level

The ILM describes 'backpressure' as:

Coolant pressure in the radiator Resistance to the flow of exhaust gases through the system Oil pressure at the pump outlet Fuel pressure in the rail

Excessive exhaust backpressure can result in:

Higher peak power Reduced engine power, poor fuel economy and elevated exhaust temperature Lower emissions and improved performance Improved throttle response

Insufficient backpressure on some older carbureted engines could:

Improve mixture distribution automatically Affect scavenging and possibly cause drivability problems Prevent engine starting Cool the engine more efficiently

Exhaust heat shields are installed to:

Increase exhaust noise Protect nearby components and body areas from excessive heat Support the drive shaft Increase catalytic converter temperature beyond design

The ILM notes that tailpipes must extend to:

Any point beneath the vehicle A safe location where fumes are directed away from the passenger and cargo areas Inside the trunk Directly under the engine oil pan

A restricted catalytic converter or muffler may be indicated by:

High power and free-revving engine Loss of power, excessive heat in the converter area and unusually high backpressure readings Improved fuel economy at high speed Low exhaust temperature

The term 'dual exhaust' in the ILM refers to systems that:

Have two radiators Use two separate exhaust paths, often with separate mufflers and tailpipes Have two intake manifolds Use two oil pumps

On light vehicles, most replacement exhaust components are:

Custom-welded pieces only Pre-bent, direct-fit components or universal pipes, mufflers and hardware supplied through parts stores Made from plastic Only available from the vehicle manufacturer

The ILM stresses that exhaust systems on heavy-duty trucks must:

Always exit ahead of the cab Be routed to clear fuel tanks, air tanks, wiring and suspension parts while meeting legal height and exit requirements Hang as low as possible under the frame Be made only of cast iron

Exhaust manifold gaskets must:

Be omitted to allow free movement Seal high-temperature gas between the manifold and head without burning out prematurely Be installed dry on both sides regardless of instructions Be reused indefinitely

The ILM notes that manifold cracking is often caused by:

Low exhaust temperatures Thermal stress from repeated heating and cooling cycles or restricted exhaust systems Coolant leaks Low oil pressure

When replacing exhaust components, parts technicians must consider:

Only pipe diameter Pipe diameter, routing, hanger locations, material (aluminized/stainless) and emission equipment locations Only the colour of the tailpipe Only the size of the fuel tank

Some vehicles use exhaust system flex sections to:

Restrict exhaust flow intentionally Allow limited movement between engine and exhaust to reduce vibration transfer Support the rear axle Control coolant flow

The ILM describes that leaks at exhaust connections may be identified by:

Visual steam only Soot deposits, noise and in some cases visible fumes Changes in coolant colour Low oil level

Exhaust system clamps are used to:

Increase sound levels Join and seal slip-fit pipe connections where welding is not used Control fuel pressure Support the transmission

The ILM points out that stainless steel exhaust components:

Cannot corrode Typically provide improved corrosion resistance and life compared with plain steel or aluminized parts Are lighter but much weaker than mild steel Are used only for heat shields

A misrouted exhaust pipe that exits too close to fuel or brake lines can:

Be left as-is safely Overheat those components and create a fire or safety hazard Improve fuel economy Reduce emissions

Exhaust donuts (sealing rings) are used at:

Fuel line connections Some manifold-to-pipe joints to allow slight movement while sealing hot gases Thermostat housings Oil drain plugs

The ILM stresses that exhaust systems should be inspected for:

Only noise levels Leaks, loose or broken hangers, corrosion, damage and proper routing Coolant condition Oil level

From a parts technician’s perspective, common exhaust parts include:

Only radiators Pipes, mufflers, resonators, clamps, hangers, gaskets and flex joints Only fuel injectors Only tires

The ILM explains that exhaust gas temperature is highest:

At the tailpipe outlet Near the exhaust ports and manifold close to the engine In the muffler In the fuel tank

Aftermarket 'performance' exhaust systems generally aim to:

Increase restriction Reduce backpressure and change sound characteristics while maintaining legal noise/emissions limits Eliminate mufflers entirely in all markets Reduce pipe diameter

Exhaust mounting hardware kits in the parts business often include:

Head bolts and pushrods Clamps, hangers, gaskets and fasteners specific to a system layout Piston rings and bearings Radiator hoses and caps

The ILM notes that exhaust systems on modern vehicles are integrated with emission control devices, meaning:

Any pipe can be replaced without considering sensor or catalyst location Oxygen sensors, catalytic converters and other devices must be correctly positioned in the system Exhaust systems no longer need hangers Backpressure is no longer a concern

Exhaust leaks ahead of oxygen sensors can:

Improve sensor accuracy Cause false readings leading to poor fuel control and drivability issues Have no effect on engine operation Only reduce noise

The ILM emphasizes that any exhaust work must consider:

Only the appearance of tailpipes Safety, noise regulations, emissions requirements and correct routing Only customer preference for sound Only material cost

On some trucks and buses, vertical (stack) exhaust systems are used primarily to:

Increase interior noise Discharge exhaust gases above the vehicle to reduce fumes at ground level Improve radiator cooling Shorten exhaust routing

From the ILM perspective, understanding exhaust systems helps the parts technician to:

Perform engine overhauls Select correct direct-fit and universal exhaust components and advise customers on safe, legal repairs Set alignment angles Replace brake pads

An exhaust system that is contacting the body or suspension can cause:

Improved ride comfort Drumming noises, rattles and possible damage to components Lower exhaust temperatures Better fuel economy