Determining if fuel has had oil added

by Had Robinson

Running a brand new 2-cycle engine on unmixed fuel is an expensive mistake.  The engine will seize after a few minutes and is pretty much ruined and will require a complete rebuild including a new cylinder, piston, connecting rod, crankshaft, and bearings – and maybe more.

If an engine has been run with the proper mix and, for some reason, gasoline without oil is introduced into the fuel system the damage is not as bad, at least if the error is discovered the first few minutes of running.  The oil pools in the crankcase and protects the main bearings and the connecting rod bearings.  In this case, only the cylinder and piston may need to be replaced but not the rest of the engine.

Hopefully, everyone reading this is using AMSOIL Dominator (a 100% synthetic oil which is made for racing 2 stroke engines) which has a red dye in it.  It is so easy to see the dye in the paramotor fuel tank.  However, the mix ratio may still be incorrect.  Most 2 stroke oils contain dye and pure unleaded gasoline is colorless so the first clue that the oil is in the gasoline is to look at the paramotor tank.

I am really picky this because I have engines that required different oil mix ratios and getting this all mixed up could be an expensive mistake.

However, if the fuel is colored, it will not be as clear whether there is oil present and these steps can be done.

  1. Pour a couple of tablespoons of the suspect fuel in a clean white bowl.
  2. Do the same with fuel you KNOW has not been mixed with oil in another bowl.
  3. Let them sit awhile, occasionally swirling the fuel near the edges of the bowl.
  4. The fuel with the oil will leave a distinct ring of oil (usually red or blue) in the bowl because it does not evaporate.

This test will not tell you the ratio of the mix.  Hopefully, you already know this....

In the photo below, the bowl on the right contained the fuel mixed with oil.  The oil is clearly visible as a ring around the bowl.  The bowl on the left contained unmixed fuel. The blue color of the residues is due to the color of the oil.  You want to have the bowl with the unmixed fuel as a standard of comparison.  Caution: AVGAS has a blue dye which can be confused with some 2 stroke oils.

oil in fuel test

Note: It is always a good idea to put a tag on the fuel container to indicate that it has been mixed with oil at the required ratio.  A piece of cheap, thin plywood on a piece of glider line works well.  Adding a piece of masking tape with the date purchased and a note if any additives have been introduced will help insure that you are using fresh fuel.  If the fuel is unpreserved and over a month old, it can be dumped into the nearest automobile.  Fuel management is extremely important for the long term health of a paramotor.

NEVER refill a fuel container without first removing any labels!

gas can tag to indicate oil has been added

We have received engines where the pilot forgot that he did not add oil to the gasoline and wrecked the engine, a very expensive mistake.