I've heard that one for years.
It was common advice decades ago to pour a little transmission fluid in the gas tank because people believed it would lubricate injectors, clean carbon, or even help the valves.
Years ago, on older carbureted engines, some people probably got away with it.
But on today's vehicles? I wouldn't recommend it.
Modern engines have oxygen sensors, catalytic converters, and sophisticated fuel injection systems that were never designed to burn transmission fluid.
Could a small amount instantly ruin your engine? Probably not.
Would I intentionally pour it in there? Absolutely not.
If you're trying to clean the fuel system, there are products specifically designed for that purpose. They're tested to work with modern fuel systems without risking damage to expensive components.
One thing I've learned over the years is this:
Just because something worked in 1975 doesn't mean it's a good idea in 2026.
Vehicles have changed dramatically.
The old tricks that worked on carburetors, points ignitions, and simple automatics don't always translate to today's electronically controlled engines and transmissions.
So my advice is simple:
Keep transmission fluid in the transmission, engine oil in the engine, and gasoline in the fuel tank. Engineers designed each fluid for a specific job, and it's hard to improve on that.
Sometimes the best maintenance isn't an old garage trick—it's using the right fluid in the right place.