Car Mechanics (UK)

Ex­haust sys­tems

Ev­ery­thing you need to know about fix­ing and re­plac­ing your ve­hi­cle’s ex­haust sys­tem.

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In the early days of mo­tor­ing, a typ­i­cal ex­haust sys­tem was re­spon­si­ble for not only car­ry­ing toxic emis­sions away from the pas­sen­ger com­part­ment but also re­duc­ing the noise caused by the gases es­cap­ing the en­gine at high ve­loc­ity.

“To­day, these are not the only func­tions,” says Doug Bent­ley, tech­ni­cal head of re­search and devel­op­ment at Klar­ius Ex­hausts of Chea­dle, Stafford­shire and our tech­ni­cal ad­viser for this fea­ture. “Aside from in­flu­enc­ing en­gine ef­fi­ciency, the mod­ern ex­haust sys­tem is cru­cial to pol­lu­tant con­trol and cur­tails the emis­sions of hy­dro­car­bon (HC), ni­trous ox­ides (NOX) and par­tic­u­lates (PM).”

The times they are a-changin’

A ve­hi­cle’s orig­i­nal ex­haust sys­tem is de­signed to com­ple­ment the en­gine, en­abling it to meet the emis­sions re­quire­ments set by the Euro Stan­dards of Whole Ve­hi­cle Type Ap­proval. It also in­flu­ences per­for­mance and fuel econ­omy.

“A re­place­ment ex­haust sys­tem must per­form to the same stan­dards, at the very least, to those met by the orig­i­nal sys­tem,” says Doug. “It is pos­si­ble for a low-grade re­place­ment to cause a car to pro­duce higher than intended emis­sions, or cause the en­gine mal­func­tion in­di­ca­tor lamp (MIL) to il­lu­mi­nate, thereby in­creas­ing the like­li­hood of an MOT test fail.”

Due to lack of leg­is­la­tion in the UK, many ex­hausts sold and fit­ted are not tested and ap­proved thor­oughly. Most driv­ers are com­pletely un­aware that their ‘bar­gain’ ex­haust sys­tem can be a false econ­omy in the long run, due to it in­cur­ring ex­tra fuel costs. The ex­haust sys­tem also main­tains an op­ti­mum amount of back pres­sure, which is crit­i­cal to power, econ­omy and pol­lu­tion con­trol.

In re­cent years, ex­haust-mounted after-treat­ment sys­tems have been fit­ted to lower the ex­pelled quan­tity of harm­ful gases that are re­leased into the at­mos­phere. These in­clude not only treat­ment hard­ware, such as cat­alytic con­vert­ers, gaso­line/diesel par­tic­u­late fil­ters (GPF/DPF), EGR valves, NOX traps and SCR (Adblue) sys­tems, but also mon­i­tor­ing equip­ment such as Lambda/oxy­gen and pres­sure dif­fer­en­tial sen­sors that feed elec­tri­cal sig­nals to the en­gine ECU.

The pro­lif­er­a­tion of car mod­els and en­gine choices has also af­fected the re­place­ment ex­haust buy­ing process, as Doug ex­plains: “As a long­stand­ing emis­sion con­trol prod­ucts man­u­fac­turer, gone are the days of us mak­ing sev­eral part num­bers in large quan­ti­ties. Now, we sell a sim­i­lar num­ber of sys­tems, but over a hugely ex­panded parts range. We de­velop around 250 new ex­haust sys­tems an­nu­ally. Orig­i­nal ex­hausts now last longer and get re­placed less of­ten but, to coun­ter­act this, the va­ri­ety and num­ber of cars has in­creased. We now sell a more di­verse range of prod­ucts, of a higher tech­ni­cal com­plex­ity.”

Buy­ing ad­vice

The ex­plo­sion of dif­fer­ent part num­bers, of­ten with very sub­tle changes be­tween dif­fer­ent spec­i­fi­ca­tions of the same ba­sic car model, makes it more likely that you and your sup­plier will source the wrong part. Klar­ius re­ports that 80% of calls that it re­ceives through its cus­tomer helpline are due to the in­cor­rect parts be­ing or­dered. If the mo­tor trade is get­ting it wrong, then the rel­a­tively in­ex­pe­ri­enced DIYER is also likely to make a mis­take.

“Take the Vaux­hall Vec­tra 1.8 petrol,” says Doug. “It may have one en­gine water pump listed, but the same model may have 20 dif­fer­ent options for the ex­haust.”

Ex­haust com­po­nents are also very dif­fi­cult to cat­a­logue. Klar­ius finds that mo­tor fac­tors can make in­cor­rect as­sump­tions, when tak­ing an or­der. Although you might think that an ex­haust that has been iden­ti­fied by a ve­hi­cle num­ber­plate will be ex­actly right, things are not quite that sim­ple. Not only might the ex­haust cat­a­logue ex­clude all of the var­i­ous options, but the sales­per­son might also se­lect the wrong part num­ber, or the first one, listed on the com­puter screen.

When or­der­ing, it’s help­ful to pro­vide ad­di­tional de­tails. Ex­hausts might be shaped dif­fer­ently for dif­fer­ent body for­mats of the same model – saloon, es­tate or hatch­back, for ex­am­ple – while cat­alytic con­vert­ers, or DPFS, might have dif­fer­ent pre­cious metal con­tents be­tween Euro III/IV/V emis­sions stan­dards. Even men­tion­ing that your car has a chrome tailpipe trim will help se­cure the cor­rect part.

De­spite ex­haust sys­tems last­ing longer than they did on cars made 20 years ago, Doug says these new tech­nolo­gies have pre­sented busi­ness op­por­tu­ni­ties for Klar­ius, be­cause it is not common knowl­edge that burn­ing a gal­lon of petrol pro­duces, ap­prox­i­mately, the same quan­tity of water, which col­lects mainly within the ex­haust sys­tem. As hybrid en­gines tend to switch them­selves off, their ex­haust sys­tems tend to run cooler, pro­vid­ing less opportunit­y for the mois­ture to es­cape. In­stead, it con­denses into an acidic liq­uid and cor­rodes the ex­haust sys­tem from the in­side out. It is no co­in­ci­dence that one of Klar­ius’s most pop­u­lar re­place­ment sys­tems is for the Toy­ota Prius.

Fall­ing off the perch

De­spite Klar­ius’s ethos of stock­ing ex­hausts for ev­ery make and model, ve­hi­cles no longer in pro­duc­tion have to be delisted at some point, which tends to be when there has been zero de­mand for two years.

“Take the Vaux­hall Corsa B as an ex­am­ple of how de­mand de­creases as more ve­hi­cles are scrapped,” ex­plains Doug. “We used to sell 2000 back si­lencer boxes for that model ev­ery month. Now, the fig­ure is around 60.”

While Klar­ius main­tains an ex­haust stock for older mod­els, a new batch is not com­mis­sioned once it has been de­pleted and the tool­ing is ei­ther archived, or scrapped. This de­ci­sion is made on a case-by-case ba­sis. For ex­am­ple, while Bri­tish Citroën XM ex­haust sales are low, this is not the case in France. Should your car have a delisted sys­tem, Doug says that the best al­ter­na­tive is a man­u­fac­turer of be­spoke sys­tems. Most of those spe­cial­ists of­fer ei­ther mild, or stain­less-steel options. How­ever, be aware that stain­less-steel also has lim­i­ta­tions. While the ma­te­rial is more cor­ro­sion-re­sis­tant, it is also more brit­tle than mild, or alu­minised, steel and cracks tend to be preva­lent, es­pe­cially on bends and welds. Ad­di­tion­ally, the qual­ity varies, so some of these fit-for-life sys­tems may last longer than oth­ers. The best ad­vice is to seek a re­spected man­u­fac­turer that makes ex­hausts from the more ex­pen­sive but su­pe­rior 304-grade of stain­less-steel and to read any war­ranty con­di­tions very care­fully.

This ad­vice also ap­plies to off-theshelf ex­hausts. As Doug ex­plains: “Klar­ius sys­tems, for ex­am­ple, have a war­ranty of up to three years. Yet we make it a stip­u­la­tion that all rub­bers and mounts are re­placed; oth­er­wise, the new ex­haust sys­tem might be ex­posed to more vi­bra­tion and stress than is ex­pected un­der nor­mal con­di­tions. The ma­jor­ity of sell­ers re­tail re­place­able mounts un­der dif­fer­ent part num­bers, so check that they are supplied with any new sys­tem.”

 ??  ?? More than just pipes, the ex­haust sys­tem af­fects the ef­fi­ciency of the en­tire en­gine.
More than just pipes, the ex­haust sys­tem af­fects the ef­fi­ciency of the en­tire en­gine.
 ??  ?? The front sec­tion of ex­haust sys­tems houses the pol­lu­tion con­trol equip­ment, plus myr­iad sen­sors. Some sys­tems com­bine the ex­haust man­i­fold and tur­bocharger hous­ing as a sin­gle part.
The front sec­tion of ex­haust sys­tems houses the pol­lu­tion con­trol equip­ment, plus myr­iad sen­sors. Some sys­tems com­bine the ex­haust man­i­fold and tur­bocharger hous­ing as a sin­gle part.
 ??  ?? You do not know what is in­side a non-type Ap­proved cat­alytic con­verter or DPF un­til it is cut open. The item pic­tured left has half the brick size, com­pared to the ap­proved item (on the right) and the lighter colour in­di­cates the pres­ence of fewer pre­cious met­als.
You do not know what is in­side a non-type Ap­proved cat­alytic con­verter or DPF un­til it is cut open. The item pic­tured left has half the brick size, com­pared to the ap­proved item (on the right) and the lighter colour in­di­cates the pres­ence of fewer pre­cious met­als.
 ??  ?? On ex­haust man­i­folds, studs and nuts tend to cor­rode and can snap on re­moval. If you en­gage an en­gi­neer­ing works to re­place the studs – an in­ex­pen­sive job – ask them to check the surface is flat and skim it, if nec­es­sary.
On ex­haust man­i­folds, studs and nuts tend to cor­rode and can snap on re­moval. If you en­gage an en­gi­neer­ing works to re­place the studs – an in­ex­pen­sive job – ask them to check the surface is flat and skim it, if nec­es­sary.
 ??  ?? Ex­haust gases can not only es­cape through a dam­aged ex­haust but also broken gas­kets. The points at which the ex­haust man­i­fold gas­ket failed were ob­vi­ous in this case.
Ex­haust gases can not only es­cape through a dam­aged ex­haust but also broken gas­kets. The points at which the ex­haust man­i­fold gas­ket failed were ob­vi­ous in this case.
 ??  ?? DPFS are equipped with tem­per­a­ture sen­sors. They are im­por­tant but del­i­cate com­po­nents.
DPFS are equipped with tem­per­a­ture sen­sors. They are im­por­tant but del­i­cate com­po­nents.

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