Yes sugar in a gas tank can ruin a car especially if the sugar gets into the fuel system and then gets through the fuel filter and into the fuel lines, fuel injectors etc.
If someone dumps sugar into your gas tank then a little bit is unlikely to cause much damage if any because the small amount of sugar would be dissolved into the gasoline if you have a full tank of gasoline.
But if your gas tank is not too full and a few bags of sugar get dumped into your gas tank then it can cause issues.
I remember some teens who thought it was funny to dump some sugar into my gas tank one night and I caught them and ran them off with a shotgun.
I had to empty the gas tank and at least they only got just a tiny bit into the gas tank which was not much of a problem.
I pumped the best part of the gasoline out and then cleaned the sugar out of the bottom of the tank.
But if they dumped more sugar into the gas tank without me knowing then I would likely have been stranded somewhere.
Those things they do are not funny and its not a thing you should do just because you're a teenager.
The cost to flush out a gas tank ranges from $100.00 to $500.00 depending on the shop the does the job and how hard it is to get to the gas tank.
Some vehicles such as a truck are easier to remove the gas tank while some cars are harder to remove the gas tank.
Most gas tanks I flush out at my shop cost the person $150.00 for dropping the gas tank and then flushing it out.
Or sometimes I'll just recommend the replacement of the gas tank if it's really dirty and the cost of the new gas tank is about the same cost as the labor charges for flushing it out.
If your car gets bad gas then the car will likely stall out, may be hard to start or may not even start all.
Getting bad gas in your gas tank is a huge problem because it requires dropping the gas tank and then draining out all the bad gas and then cleaning the tank out as well as the fuel lines, replacing fuel filter and cleaning or replacing fuel injectors as well.
Getting bad gas in your car can ruin the fuel injectors and cause your car to fail to start or run rough.
A car needs the freshest gasoline available to allow the cars engine to run properly and when bad gas gets into the fuel system it can cause damage.
The fuel filter can become clogged, the fuel pump can get clogged or ruined and your fuel lines can also become clogged and your fuel injectors can become clogged.
If you have bad gas in your car it will run rough, be hard to start, engine will stall, engine may not start or the engine will run rough.
If you have bad gas in your car it needs cleaned out of the tank and then the fuel lines need to be cleaned out as well.
A new fuel filter will be needed and your fuel injectors may need replaced or cleaned.