A wastegate controls a turbocharger’s boost by letting some exhaust gas bypass the turbine. Without it, the turbo would keep spinning faster as engine speed rises and make more boost than the engine can safely take. When boost reaches the target, an actuator opens the wastegate valve, routing exhaust around the turbine so it stops accelerating and boost levels off.
Internal vs external wastegates
| Internal | External | |
|---|---|---|
| Location | Built into the turbine housing | Separate valve on the exhaust manifold |
| Common on | Most factory turbo cars | High-output and racing builds |
| Boost control | Good for factory boost levels | More precise at high boost and flow |
What does a wastegate actuator do?
The actuator opens the wastegate. Older and simpler systems use a spring and diaphragm operated by boost pressure; many modern engines use a vacuum or electronic actuator controlled by the engine computer, which lets it target boost precisely.
Wastegate problems
- Stuck closed: overboost, which can trigger limp mode and code P0234.
- Stuck open or leaking: low boost, sluggish response, code P0299.
- Rattle: a worn wastegate flapper or linkage can rattle at idle or on deceleration.
- Boost sensor faults: codes such as P0236 can look like wastegate problems.
What does a wastegate do on a diesel?
Many older diesel turbos use a wastegate the same way. Many modern diesel trucks instead use a variable geometry turbo, which controls boost by changing the angle of vanes around the turbine rather than bypassing exhaust; see variable geometry turbo. The Fleece Cheetah turbos we list for the 6.7 Cummins are VGT units at $3,099.00; see 6.7 Cummins turbo.
Boost creep
If a wastegate is too small for the exhaust flow of a modified engine, it cannot bypass enough gas at high rpm, and boost keeps climbing past the target even with the gate fully open. This is called boost creep. It is one reason high-output builds move to larger or external wastegates. On a stock engine, boost that climbs past normal points to a stuck or disconnected wastegate.
Checking a wastegate
With the engine off and cool, the wastegate arm should move freely through its range on most designs. Check that the actuator rod is connected, that vacuum or boost lines are not cracked, and that the electronic actuator, if fitted, has no fault codes.
Wastegate vs blow-off valve
A wastegate works on the exhaust side to limit boost. A blow-off valve works on the intake side, venting pressure when you close the throttle; see what does a blow-off valve do?
Related
See what is turbo lag?, turbo failure symptoms and what does an intercooler do?
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