Coughing and Wheezing?

| April 07, 2005

Mufflers are a valuable component of the exhaust system. When working properly, mufflers provide not only a quieter ride and enhance engine performance, but are also shown to reduce fatigue associated with sustained noise.

Ken Kicinski, chief engineer OE exhaust products at Fleetguard Nelson says, “The total volume of the muffler or mufflers dictates the end result in terms of sound level.” This tells us why so many trucks use dual mufflers: You can easily get twice the muffler volume available with single exhaust. And, that increase in volume means quieter operation.

“Internal design is the next factor,” he reports. Clever design will lower sound level with a minimal effect on backpressure.

These are the M100465 (horizontal) and M065140 heavy truck mufflers from Donaldson Co. The M065140 is an off-road muffler with aluminized steel construction, and black matte high-temperature finish.

Just what is backpressure? It’s the restriction of the muffler and exhaust system piping that creates pressure in the exhaust system that begins where the exhaust exits the turbocharger.
Expansion is the key to engine operation. Your engine takes in air, and after compression and combustion, expansion begins during the power stroke, as the air flows through the turbocharger’s exhaust nozzle. As expansion occurs, the energy added during combustion is converted to power to drive the truck down the road and to spin the turbo. If there is too much backpressure in the exhaust system, the expansion process is stopped prematurely, costing you money and reducing engine performance.

Wear and Tear

There is disagreement about just how much condensation may rust exhaust system parts, but all parties agree diesels create relatively little of it. Yet it’s pretty clear a truck chugging away at a low idle with the coolant well below operating temperature will be hard on its exhaust system. So, at least idle the engine fast enough to keep coolant at 180 degrees.
Ron Buchler, a senior engineer truck and bus product with the Walker Heavy Duty Exhaust Division of Tenneco Automotive, says that even though trucks rarely sit for long, it does happen. Shutting a truck down with condensation in the muffler and then allowing it to sit for a long time would be a bad idea.

Kicinski points out that Caterpillar diesels with ACERT, and some medium trucks, already have catalytic mufflers. These definitely need to be run hot – preferably under load.
Another helpful hint, says Kicinski, is to try to keep wash water out of the exhaust system. “Drive it after going to a truck wash, to dry out the system,” he says.

Unfortunately, rain water can also be detrimental because “

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