why does putting sugar in a gas tank ruin a motor. what does the sugar actually do to the motor
Well there seems to be some question about sugar doing any damage. Of course if you get enough in there …
http://kwc.org/mythbusters/2004/07/mythbusters_scuba_diver_in_a_f.html
Yeah, the above link is to the results of a Mythbuster episode in which Adam and Jaimie tested the sugar-in-gastank story and showed it is just a myth.
Any sugar that’s not disolved in the gas will be filtered by a decent gas filter. And then if anything gets through that…the WORSE it could do is clog the injectors.
Sugar can damage the fuel system but the chance of it causing any engine damage is very, very slight. In the case of the latter, and it’s a real stretch, it’s possible that if someone continued to operate for a lengthy time a poorly running vehicle due to sugar that converters could overheat, clog, etc. This could in turn cause engine overheating or emission control failures (EGR, O2, etc) but that is a fairly weak theoretical.
Well, this has put holes in the plots of many 1970’s TV shows I remember where some dastardly person has ruined a car by putting sugar in the gas tank. What can you believe any more?
The trouble back then was the cheap knockoffs of the Holley carbureators. The knockoff company, Hollywood Carbureators, made carbs that had very interesting properties. Sugar would render them inoperable, and their fuel-air mixture was so volitile that merely running into a building would cause the car to explode in a spectacular fireball - usually, however, giving the occupant(s) enough warning to run 3 steps and then take a flying leap to the ground as though stealing 3rd base. Female passengers would generally lose the top two buttons of their blouse during this maneuver but it was never determined if this was caused by the explosion or the impact with the ground.
I hear the consensus saying,“Yeah, you can put sugar in the gas tank.” This reminds me something my family Doctor once told me: that it’s a myth that coffee is bad for you- “You can drink some coffee everyday if you want!” Well hell, cars are always being compared to women- “She runs like a bat outta Hell!”; so why shouldn’t we try to make’em sweeter? I miss the good old days before you had to be able to open the car doors in order to pop the hood- you could just put sand in the oil filler. Now there’s no myth. Just kidding…
It’s pretty hard to do any damage to a car with sugar any more, but it used to be possible. The sugar had to get all the way through the fuel line and into the combustion chambers. That alone is very difficult to do these days, since the fuel filters catch most if not all the sugar. Once upon a time the fuel filters were pretty porous, and in fact not even there at all on some cars.
But if the sugar did manage to find its way into the combustion chambers it would burn right along with the fuel. If you’ve never seen sugar burn, give it a try sometime. It results in pure carbon and a little water vapor. The carbon is fluid and sticky while hot, then solidifies when it cools. Running a load of sugar through an engine would result in a whole lot of carbon forming inside the combustion chambers. Once the engine was shut off, it only took a few seconds to solidify, then the engine was in deep trouble. Valves would be stuck open, lots of rock hard carbon between the pistons and cylinder walls, etc, etc. The only cure was a complete engine disassembly and de-carboning.
As I said, It doesn’t happen any more, because the fuel filters clean almost anything out of the fuel that doesn’t belong there, and I don’t know that sugar would make it through an injector even if the filter didn’t stop it.
The reason sugar can ruin a fuel injected system is that the fuel tank strainer will stop the majority of it with the smaller stuff being caught by the filter. This means the pump is having to work much harder and is going to shorten the life of the pump.
The very small stuff that makes it through the fuel filter is probably going to get caught in the injectors and over time will plug them up because there is a very tiny, extremely fine screen inside of those injectors.
Simpler times…
What’s more harmful; a pound of sugar or a pound of beach sand? 
I don’t know. Which is heavier?