A wastegate is a valve that sits in front of the turbo compressor.
Here, let’s go over how a turbo works, and then it’ll make sense:
As you drive, exhaust exits the engine and heads down the exhaust pipe to exit out of the muffler. You can think of exhaust as wind going through the pipe.
Much like a windmill, a turbo uses a turbine to capture that wind energy. It then spins a turbine that’s sitting in the air intake, which acts as a pump to force more air into the engine than it would get normally. The engine uses that extra air to burn more fuel, which makes bigger explosions, which gives you more power.
But if you go overboard on this, and introduce too much pressure in the intake (this pressure is called “boost,”) then you start breaking things.
That’s where the wastegate comes in. Once the pressure gets to a preset limit, the wastegate starts opening, which channels some of the exhaust flow away from that turbine, so that it doesn’t spin too fast and create too much boost.
If your mechanic is right and the wastegate isn’t closing properly, then this means that it’s redirecting exhaust flow before the pressure gets to that limit, which means that you aren’t getting as much boost as you should be getting.
The end result in this is that your car is going to be slower. When you’re tooling around on those mountain roads in Washington, it’s going to be a lot slower than it should be.
However, this isn’t a situation that should damage the car - but it is something you’re probably going to want to replace at some point so you can get that lost power back.