Exhaust systems: combatting corrosion

drain-hole-4-v1The effects of corrosion can seriously compromise the lifespan of an exhaust system. Bosal Automotive & Industrial Components, one of the world’s major suppliers of complete exhaust systems, advises garages and workshops on some optimum ways to prevent both internal and external corrosion.

What causes internal corrosion?

When a cold engine is started the silencer heats up; when the system cools down, approximately 0.5 litres of condensate can be produced. This amount will vary dependant on the duration of the journey and the driving mode. Most of the condensate will evaporate but on short journeys the condensate can remain in the silencer. The left over condensate has a very low pH value, which means high acidity content. This acid will gradually cause the exhaust to corrode from the inside and shorten its lifespan.

How does this affect the performance of a vehicle?

A car’s engine performance is at its optimum when the gas flow in the exhaust is smooth and unhindered. When the interior of the exhaust begins to rust the gas flow can be disrupted; consequently, this increases backpressure and lowers engine performance.

How can internal corrosion be prevented?

To counter this negative effect, Bosal has introduced a drain hole to its exhaust systems, mainly in the rear silencer to release the condensate. The drain hole is a formed 2mm hole at the bottom of the inlet endcap of the lowest part of the exhaust system; this prevents the build-up of corrosion and prolongs the life of the exhaust.

Will the drain hole cause excess gas leakage and/or increased noise?

The drain hole may allow a small amount of exhaust gas to escape. This leakage, which complies with EC regulations, is minimal and will not affect the car’s performance. In terms of increased noise, any exhaust gas that the drain hole may allow to escape is inaudible and so will not affect the level of noise.

Will the drain hole affect a vehicle’s M.O.T.?

In short, no. An exhaust system will not fail an M.O.T. for having a drain hole.

What happens if the drain hole is blocked?

The drain hole should not be blocked; doing so will invalidate any warranty.

What causes external corrosion?

External corrosion occurs on parts of the exhaust system that are left exposed beneath the vehicle. A familiar example of external corrosion occurs when roads are salted during winter, as salt attacks the exposed pipe work and the wall of the box. Any repeated exposure may cause external corrosion.

How can external corrosion be avoided?

Uniquely, Bosal uses high corrosion resistant aluminised steel both in and outside exhaust

systems. This considerably reinforces the products, making them resilient to even the most

heavily salted roads. This combination of superior materials and the drain hole concept extends the life of Bosal’s exhaust systems.

Want to find out more?

For all technical queries relating to Bosal Exhaust Systems, please contact the Technical Help Desk on 0800 374710. For further details on Bosal Automotive & Industrial Components, please call 01772 771000 or email baic@eur.bosal.com. Alternatively, visit www.bosal.co.uk to find the latest products.

Bosal Exhaust Systems: delivering proven, innovative solutions

  • OE expertise in design, development and manufacturing
  • Excellent time to market
  • Advanced in-house R&D facilities guarantee innovative product solutions
  • Cutting-edge acoustic measurement techniques for maximum comfort
  • Rigorous test programmes for maximum durability


OE competence for the aftermarket

  • All manufacturing plants are TÜV certified to ISO/TS16949 OE quality standards
  • All products are type approved in accordance with the European directive for replacement silencing systems 70/157
  • One to one exchangeable with OE parts
  • First-class fit first time
  • Proven quality performance over the product life cycle


For more information, interviews or images please contact:

Claire Brown or Kimberley Hornby, Hornby Whitefoot PR

Tel: 07787 505963         E-mail:claire@hornbywhitefootpr.co.uk

Tel: 01858 681122         E-mail: kimberley@hornbywhitefootpr.co.uk