How Turbo Wastegates Work, And What Happens If They Stick

Over the past 25 years, turbochargers have gone from a relative rarity to a fixture of the new-car buying experience. Where in 2000 only 1% of new cars had the technology, according to the Environmental Protection Agency's November 2024 Automotive Trends Report, 35% of new cars sold in 2023 had one. While the concept of turbocharging has existed since early in the 20th century, advances in metallurgy and technology have allowed what was formerly a reliability nightmare to become a staple of the automotive ecosystem, with demonstrated applications from family sedans to F1 race cars.

Turbochargers work by leveraging exhaust gases to spin a compressor that forces air into the combustion chambers at higher pressures. Automakers have realized that turbos let smaller engines produce the same power as their larger naturally aspirated brethren, saving weight, and therefore improving fuel economy.

A key development over the past 20 years, however, is engineers' ability to carefully manage just how fast the turbocharger spins. Too fast, and the spinning bits inside the turbo can pit and look a bit like an orange peel from excessive centrifugal force. Too slow, and none of the benefits are delivered until the turbo can spin up, in a phenomenon known as turbo lag. As the driver asks for more power and more exhaust gases spin up the turbocharger, a wastegate can allow excess gas to go around the turbo itself, keeping the whole thing spinning at its ideal operating speed.

A wastegate is a relatively simple part, just a valve and spring, with the spring calibrated to let the valve open when the pressure gets above a certain threshold. Those values are carefully selected by the engineers based on the type and size of the turbocharger used, to avoid undue stresses on the turbo's internal parts.

There are two types of wastegates, external wastegates, where the valve is remote from the turbo, and internal ones with the valve directly integrated into the turbo housing. An internal system is more likely at lower pressures and when the fit in the engine is tighter. External wastegates are larger and can be placed away from the turbo, and are thus more flexible, serviceable and tunable.

Either way, the key function of the wastegate is to manage turbine speed, and the advent of electronic wastegates allows even more precise control. An electronic wastegate opens and closes the wastegate via a small servo in response to commands from the car's computer. Combining that with electronic measuring of turbo speed can let the turbo spin within 2% to 3% of its maximum speed and maintain reliability. 

If a wastegate gets stuck closed or partially blocked, typically it doesn't take long for the problems to become apparent. Without the wastegate to relieve the excess gas, the turbo will produce too much boost by spinning too quickly. With these machines already operating close to their design limits, the side of the turbo that deals with exhaust gases can overheat and melt or, more likely, warp. Considering the spin rate, maintaining rotational balance is essential, and any small bending of the shaft connecting the exhaust and intake sides can quickly cause fatigue and failures.

These problems may present with relatively minor symptoms at first, reduced power or a smoky exhaust being the most common. But from there, turbo whine under acceleration and blue exhaust at engine start are likely, and also urgent signs that attention is required. Then the engine will be massively down on power, similar to the feeling of turbo lag but without any resolution as the rpm increase. Any period of sustained full or mostly full throttle will make the symptoms apparent.

Nevertheless, automakers have clearly decided that the benefits of turbocharging outweigh these potential issues, and there are no signs that a well-maintained turbocharged engine cannot be every bit as reliable as a naturally aspirated one, so long as the wastegates function as designed.