Sugar in the gas tank? Questions and answers

Feb 1, 2009 by

Over the past few months we have investigated several “sugar in the gas tank” cases. Here are some common questions related to our investigations.
What is the difference between fuel injection (FI) and carburetors in terms of plumbing and how they work?
Carburetors combine liquid gasoline and air to form a combustible vapor mixture, which is drawn into the combustion chamber through the intake manifold. FI sprays liquid fuel into the intake manifold (indirect injection) or the cylinder itself (direct injection). FI uses much smaller apertures than a carburetor to deliver the fuel and is much more precise. The two systems have the same basic function, mixing fuel and air at somewhere between 13 parts of air to 1 part of fuel (a rich mixture) to a more lean 14.5 to 1 ratio. In general, rich produces more unburned fuel in the exhaust (more pollutants to deal with), while leaner produces higher temperatures (hard on valves and catalytic converters). Carburetor models have a fuel pump that delivers 3 to 5 PSI of fuel through one line to the carburetor. On fuel injection models, it is a bit different. The fuel injection pump delivers 30 to 35 PSI to the fuel injectors and what is not used and sprayed into the engine is returned to the fuel tank by a fuel return line. The fuel is constantly moving through the lines to the engine and back to the fuel tank. The fuel injectors are opened by pressure and, in most cases, are electronically controlled.

What filters are in both, and how small do they filter out or down to, assuming OEM?
Carbureted models usually have one inline filter and it stops most foreign particles from entering the carburetor. Fuel injected vehicles usually have a screen in the tank (often called a sock because of its shape) attached to the fuel pump that is also inside the tank. This filters the large particles. A second fuel filter then filters out the very small particles and is located somewhere between the tank and the engine. Some vehicles have a primary fuel pump in the fuel tank and secondary pump located outside the tank. Standard fuel filters are usually designed to stop particles in the 15 to 50 micron or larger range. Some filters can remove particles as small as 2 microns. A human hair is 80 to 100 microns (a micron is 39 millionths of an inch). Some vehicles have two filters in the fuel line coming from the fuel tank.

What size are table sugar granules?
Sugar granules vary in size from 100 to 2,000 microns. Generally table sugar is 300 to 400 microns. Confectioner’s sugar, or powdered sugar, is a mixture of cornstarch and sugar. The cornstarch is added to keep the fine sugar particles from clumping together. These sugar particles are generally from 50-100 microns. The cornstarch particles are generally less than 20 microns.

Does sugar dissolve in gasoline?
Not in appreciable amounts (less than a teaspoon for a full tank of gas).

Do gasoline and water mix? 
No. Think of a bottle of vinegar and oil salad dressing. Oil does not dissolve in vinegar (vinegar is basically infused water), but if you shake it, they will mix for a while, and then separate with the oil floating on top of the vinegar. The same holds true with gasoline and water. The water settles to the bottom of the fuel tank.

How does water get into a gas tank?
Water gets into the tank via humidity and condensation in the air. The higher the humidity, the more condensation, and the more water can collect in the tank. Water and dirt can also come from the pump of a filling station with inadequate filtration.

Then does sugar dissolve in the water in a gas tank? 
Sugar will dissolve in water, wherever it finds it. Now think about the fuel-injected vehicle. Remember the constant movement of fuel in the lines to the engine and back to the tank? That keeps everything moving; fuel, moisture and any dissolved sugar, if present-just like shaking the salad dressing. The now-sugar-contaminated water can mix with the fuel and be passed through the system, past the fuel filter to the engine. It takes a while, but it will happen. There are still undissolved solid sugar granules in the fuel tank, most likely restricting the flow through the main and secondary fuel filters.

What happens to sugar in a carburetor situation when it hits the valves?
It is thicker than gasoline so it is not vaporized and it sticks to the hot valve stem. It also sticks to various other parts of the engine as it enters i.e., intake manifold, gaskets, and surfaces of the combustion chamber.

Why is this a bad thing?
If it is a small amount it will burn away and exit via the exhaust. But that is usually not the case. What bad guy puts a “small amount” of sugar in a gas tank? As the melting/burning sugar substance builds up a tarry layer on the hot valve stem, the clearance between the valve and valve guide becomes smaller. Pretty soon, no clearance, and the valve sticks, partially open or closed. If the valve is stuck open, it can be bent or damaged by the piston when the piston strikes the valve at the top of the upstroke.

Putting sugar or water in the gas tank of a vehicle can indeed cause the engine to stall — sugar because the granules won’t dissolve in gasoline and may clog the fuel filters; water because it interrupts combustion — but neither method will produce a predictably-timed engine failure. Depending on the quantity of the foreign substance introduced, it might take minutes, hours, or even days for the stall to occur.

What happens to sugar in an FI situation?
In most cases, the injectors will clog and cause the engine to stop running before the sticky liquid gets to the valves. Remember the constant loop of fuel circulation in an FI situation? FI models also generally have smaller tolerances between the valve stem and valve guide. Most of the time the fuel injectors get clogged first and cause poor running conditions and the infamous “check engine light” comes on. Then you need to clean the gas tank, replace the fuel pump, all the filters, and most likely all of the fuel injectors. If it’s a 6 cylinder BMW, you could be looking at a repair bill in the neighborhood of $5,000!

What happens if the sugar gets to the valves?
It will become a tarry deposit on the valves and will build up thicker and thicker. In some cases, when the valve is stuck in the open position, the piston comes up and hits the valve and bends or breaks it. Now you have some serious damage.

What about a syrup solution going through filters?
This will have the same effect as granular sugar dissolved in water from condensation in the fuel tank.

Is there a difference between Coke and Pepsi?
Not to a car. They are both sugar and water mixtures and both could get pumped through the filters to the engine.

What about non-sugar or diet versions of Coke/Pepsi-would you get the same result?
The sweetener in Diet Coke is NutraSweet and for Diet Pepsi it is Aspartame. Neither sweetener is combustible. When the liquid mix of diet Coke or diet Pepsi and gasoline reach the engine, the problems listed above would most definitely occur.