5 auto shops couldn’t fix a common car problem, but the 6th mechanic used a dollar bill and solved it in seconds

A mechanic with 30 years of experience solved a tricky car problem using just a dollar bill after five other shops couldn’t figure it out. This isn’t just a fun trick. It’s a real, old-school method that quickly finds one of the most common problems in modern engines: dirty or sticky valves.

According to Motor1, the trick was shown in a viral video from the TikTok account Expert Mechanic Tricks. The technician held a U.S. dollar bill up to the car’s muffler. The bill immediately curled backward and was pulled toward the exhaust pipe. The account later confirmed that the vehicle had dirty engine valves, an issue often caused by using cheap gas.

This dollar bill trick helps detect what mechanics call “sticky valves” or a burnt exhaust valve. When an engine is healthy, exhaust gases should constantly push out from the tailpipe. If the system has a major leak or a broken part, like a bad head gasket or a broken valve seal, the muffler creates a “sucking force” instead of a steady outward blow.

Simple tricks can reveal serious engine problems

Automotive enthusiast Matt Payne, who posts diagnostic content, explains that if the bill is pulled toward the exhaust, you definitely have a problem. If your engine is fine, the pressure of the exhaust blowing out will keep the bill pushed away. Another expert, YouTuber Wayne M., notes that the logic works the same even if you use a sheet of paper instead of cash.

The cause of this problem is usually gunk and carbon buildup that forms a crusty, black substance on the valve stems. This stops the valve from sliding in and out easily when the camshaft tries to move it. The video creator shared a comparison photo showing one valve totally caked over, while the other just had some light soot. When taking your car to a shop, knowing common mechanic scam warning signs can help you avoid dishonest repair shops.

If your valves aren’t working correctly, you’ll notice some serious symptoms. You can expect a clear loss of power in the vehicle, and your gas mileage will suffer. The most annoying symptom is rough idling, which becomes really obvious when you’re stopped at a light or parked with the engine running.

If you ignore this issue for too long, that carbon buildup can cause engine misfires, increased exhaust emissions, and even long-term engine damage. Solving sticky valves doesn’t always require a complete engine teardown, depending on how bad the buildup is. Regular oil changes are essential, though experts warn about extended oil change interval risks that can harm your engine.

If the dollar bill test fails on your car, you should run an engine compression test next to get a clearer picture. For mild cases, you can try using fuel treatments and upper cylinder lubricants, like Lucas Oil or Marvel Mystery Oil. The best defense is prevention. An auto repair shop based in Sacramento, California says that regular maintenance is key. They recommend always using quality fuel and fuel cleaning additives, and making sure you drive your car at its optimal operating temperature.