A good cleaning

Compressed air filled the airplane’s exhaust system as he sprayed soapy water on the manifolds and connected pipes. Glistening purple and green bubbles began pouring out of various joints and unseen cracks. It looked like…money.

Exhaust systems are the vital but underappreciated colons of our engines, and the only place exhaust should exit from. Anything else is a leak that could introduce carbon monoxide in the cabin, or extremely hot fumes under the cowling.

How hot? Airplane exhaust gases can reach 1,600 degrees Fahrenheit. Water boils at 212 degrees, paper ignites at 451, zinc melts at 787, and aluminum at 1,220.

“The problem with aircraft exhaust systems is you don’t get a lot of indicators when things are going bad,” said Justin Bucholz, Aerospace Welding’s director of maintenance, repair, and overhaul in Minnesota. “You aren’t going to get a check engine light or exhaust pressure warning and won’t know there’s a leak.”

Repairing or replacing leaking parts is critical to safety and performance, but it’s not cheap. Fortunately, it’s possible to extend system longevity and avoid problems by following some basic guidelines.

Parts, pieces, and problems

Every GA airplane exhaust system has the same basic components. High-grade stainless-steel tubes connected to the engine block are called headers, stacks, risers, or manifolds. Some might be an alloy called Inconel that includes nickel and chromium. As with stainless steel, its melting point is around 2,600 degrees Fahrenheit.

Those heat- and corrosion-resistant components are designed to collect, direct, and discharge exhaust gases. One or more mufflers reduce noise and help stabilize pressures. In most cases, there’s a steel or aluminum shroud near the muffler collecting heat to warm the cabin or carburetor. Bringing up the rear are one or two tailpipes.

Despite their robust construction, these systems always wear out, usually from within. Exhaust is hot and corrosive. Expansion and contraction from heating and cooling takes a toll. And vibrations stress joints and welds. A well-maintained system should last an engine’s life. Otherwise, open your wallet.

For reference, a MagnaFlow exhaust system for a 2021 Ford F-150 costs around $1,000. A Cessna 182 system from Aerospace Welding (AWI) or Power Flow is at least four times higher. A big reason for the price disparity is economies of scale since Ford produced more than 700,000 of those trucks in 2021.

At AWI’s spotless production and maintenance center near Minneapolis, producing airplane exhausts involves precision pipe bending, advanced welding skills, artistry, and quality checks. It’s not an assembly line operation.

The metals used are also more robust and expensive than automotive systems. That’s because only two U.S. foundries are making sheet metal and tubes that are airplane-worthy, according to AWI and Power Flow. Prices for those materials have skyrocketed double and triple digits over the past couple of years. And, as always, FAA regulations designed to enhance safety add costs.

Save money and extend life

Your mechanic or you should comparison shop. The main options are original equipment manufacturers (OEMs), AWI, Acorn Welding and Knisley Welding, which are owned by the same organization, and Power Flow.

According to AWI’s Bucholz, “It’s not uncommon to see a three times price difference between OEM exhaust components and our FAA-approved parts.”

He cited an extreme example of an exhaust stack on a Continental engine in a popular turbocharged retractable. AWI charges $1,300. The airplane’s manufacturer charges $12,000.

AWI produces the exhaust systems for several OEMs and often gets involved during the planning process. When the OEMs say they are no longer supporting a system, AWI creates PMAs (parts manufacturing approval) to support the product. They also work with individuals to create owner-produced parts for warbirds, experimentals, and other nonstandard aircraft.

“Anything you get from us, you get a statement of work performed,” said Bucholz. “Repaired or overhauled items get an FAA 8130 airworthiness certificate. Any A&P [airframe and powerplant mechanic] can do the installation and put that paperwork in your logs.

“Hundreds of different kinds of planes have been manufactured over the years. Our goal is to help keep them flying. We want to be a safe, reliable, consistent place that offers customers great products and fair prices.”

More than 6,500 airplanes are flying with “tuned exhausts” produced by Power Flow in Florida. They are the OEM for Diamond DA40 and DA42 airplanes with Lycoming engines. They are also approved for use on a variety of airframes.

“A tuned system is optimized so exhaust gases are synchronized to work for you, not against you,” said Power Flow President Darren Tilman. “Our systems are designed to optimize cylinder efficiency. The key benefit is an increase in horsepower due to efficiency gains.”

According to Tilman, more than a decade ago a major engine rebuilder in California tested the output of a new Lycoming 320 with a conventional exhaust system versus a Power Flow system. The difference was a 24-horsepower gain in output, although more fuel was burned.

Tuned exhausts have been common in many race cars for years. Several online reviews support Power Flow’s premise, but they aren’t universal. Doing some homework is always smart, and the company offers a 60-day money-back guarantee. Although the FAA requires exhaust systems to have detailed inspections during annuals, the regulations aren’t specific. Canadian regulations specify pressure testing like my mechanic did.

If a problem is identified, only an A&P or repair station can fix it. A welder who works on cars or the like isn’t qualified to sign off such work.

“Your exhaust is thin metal,” said Bucholz. “If a fracture occurs and someone thinks, ‘Oh, I’ll just weld it,’ that can leave sharp edges that could rub on electrical or fuel lines.”

When systems are assembled, reassembled, or annualed, he strongly recommends exhaust lube be applied to moving parts such as ball joints and slip joints. McFarlane sells a well-regarded product called DAM Exhaust Lube. Its website recommends avoiding any lubricant containing graphite since it “corrodes and destroys the grain structure of stainless steel.”

AWI can evaluate individual components or entire systems, usually within three weeks. I shipped my original system to them and got a detailed list of components that needed to be repaired or replaced, along with the associated cost. I elected to install a new system. It was a few thousand dollars higher, but the peace of mind was worth it since I’m no longer exhausted worrying about my airplane’s exhaust system.

Kevin Knight is an instrument-rated owner of a Cessna TR182.