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2026. 6. 30. 작업

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What is the "dollar bill" test?

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The dollar bill test is quite simply using a dollar bill (any denomination ... doesn't have to be American currency, even) and placing it against the exhaust tip while the vehicle is idling. You are looking/listening to what the bill does while against the exhaust tip. If it just flutters there without making much noise, you have healthy exhaust valves. If it rattles against the tail pipe, you may have a burnt exhaust valve (no guarantees here), which would be a basis for further examination, such as compression and leakdown tests. What is happening is this, when an exhaust valve is burnt, it is no longer sealing against the valve seat. When idling, there is usually a great deal of vacuum created during the intake cycle. If the valve is burnt and leaking, you'll get reversion . Reversion is where the exhaust flow changes direction back toward the cylinder, which should not be happening. By placing the bill on the exhaust tip, the bill will rattle. The noise will be very noticeable. Ple